Electrical Thumb Rules-Illumination-(Part-16).

Illumination Requirements per Building & Fire Codes

Walking Surface or Area Lighting Level (Lux) Lighting Level (Lux)
NFPA 1 & 101 IFC/IBC / ICC 
New stairways 10.8 10.8
Floors & other walking surfaces (not stairs) 10.8 10.8
Assembly areas during performances 2.2 2.2


Illumination Level

Lux Level Work Activity and Function Example of User Area
20 – 80 Public walking Public parks and open-air car parks
100 – 140 Casual non-visual task Corridors, changing rooms, office restrooms
150 – 180 Some perception of detail Warehouses, stores, plant rooms, lift lobbies
200 – 240 Continuous occupation Entrance halls, dining rooms
250 – 300 Very easy visual task Public toilet, classrooms
300 – 400 Moderately easy visual task Private office, libraries, lecture theatres
500 – 600 Moderately difficult visual task Offices, laboratories, retail outlets
750 – 900 Difficult visual task Supermarkets, technical drawing offices
1000 – 1300 Very difficult visual task Operating theatres, polishing and painting plant
1500 – 1800 Extremely difficult visual task Assembly plants, inspection plants
> 2000 Exceptionally difficult visual task Precision assembly, fine work inspection


Illumination Level

Australian Standard AS/NZS 1680.2.2 under Table 3.1

Areas and Activities Examples Illumination (lux)
Interiors rarely visited where lighting is only required to aid movement and orientation Pass-though corridors and walkways; cable tunnels; indoor storage tanks 40
Areas of intermittent use for tasks of coarse detail Movement, orientation and tasks of coarse detail in areas such as change rooms, storage rooms, loading bays etc. 80
Areas that are continually used for tasks of coarse detail Simple tasks such as occasional reading of clearly printed documents for short periods or rough bench or machine work in areas such as waiting rooms and entrance halls etc. 160
Continuously occupied interiors used for ordinary tasks with high contrasts or large detail Food preparation areas; counters for transactions; school boards; medium woodworking 240
Areas where visual tasks are moderately difficult and include moderate detail with low contrast Routine office tasks such as reading, typing and writing in office spaces or enquiry desks 320
Medium level inspection work such as fine woodwork or car assembly 400
Areas where visual tasks are difficult with small detail with lower contrast Visually difficult tasks including most inspection tasks such as proofreading, fine machine work or fine painting 600
Areas where visual work are very difficult and involve very small detail with very low contrast Very difficult tasks such as fine inspection, paint retouching or fine manufacture 800
Areas where visual work is extremely difficult with extremely small detail with very low contrast Extremely difficult tasks that may require visual aids such as graphic arts inspection; hand tailoring; inspection of dark goods; extra-fine bench work etc. 1200
Areas where visual work is exceptionally difficult with exceptionally small detail with very low contrast Exceptionally difficult tasks where visual aids would be of advantage such as the assembly of minute mechanisms and jewellery and watch making 1600


Illumination Level

Illuminance Example
Full moon overhead 1 lux
Family living room 50 lux
Hallway/toilet 80 lux
Very dark overcast day 100 lux
Sunrise or sunset on a clear day. Well lit office area 400 lux
Overcast day, typical TV studio lighting
Full daylight (not direct sun) 10000-25000 lux
Direct sunlight 32000-130,000 lux


Illumination Level

IS 3646 (PART-1) 1992

Types of interior or activity illuminance (lux)
Entrance Halls, Lobbies, Waiting Rooms 150-200-300
Inquiry desks  300-500-750
Gatehouses  150-200-300
 Circulation Areas
Lifts 50-100-150
Corridors, Passageway, stairs 50-100-150
 Escalator, travellators 100-150-200
Medical and First aid Centers
Consulting Rooms, Treatment Rooms 300-500-750
Rest Rooms 100-150-200
Medical stores 100-150-200
 Staff Rooms
 Changing, locker and cleaner Rooms, Cloakrooms, lavatories 50-100-150
 Rest Rooms 100-150-200
 Staff Restaurant
Canteens, cafeterias, dining rooms Mess rooms 150-200-300
Servery, vegetable preparation, washing-up area 200-300-500
Food preparation and cooking 300-500-750
 Food stores, cellars 100-150-200
Switchboard rooms 200-300-500
Telephone apparatus room 100-150-200
Telex room, post room  300-500-750
Reprographic room  200-300-500
Building Services
 Boiler houses General 50-100-150
Boiler front 100-150-200
 Boiler control room 200-300-500
Control rooms 200-300-500
Mechanical plant room 100-150-200
Electrical power supply and distribution Room 100-150-200
Store rooms 50-100-150
Car Parks
 Floors 5 to 20
 Ramps and Corners 30
Entrances and Exits 50-100-150
Control Booths 150-200-300
 Outdoor Car Parks 5-20 5 to 20
Ticket counters, checking, desks And Information desks 300-500-750
Departure lounges, other waiting Areas 150-200-300
 Baggage reclaim 150-200-300
 Baggage handling 50-100-150
 Customers and immigration halls  300-500-750
Concourse 150-200-300
Railway Stations
Ticket office 300-500-750
Information Office 300-500-750
Parcels office, left Luggage Office General 50-100-150
Counter  150-200-300
Waiting rooms 150-200-300
Concourse 150-200-300
Time table 150-200-300
Ticket Barriers  150-200-300
Platforms (covered) 30-50-100
Platforms (open) 20
 Ticket offices 300-500-750
Information offices  300-500-750
Concourse  150-200-300
Loading Areas 100-150-200
 Assembly Halls
General  200-300-500 3
Teaching Spaces
General  200-300-500
 Lecture Theatres
 General 200-300-500
Demonstration benches  300-500-750
Seminar Rooms  300-500-750
 Art Rooms 300-500-750
 Needlework Rooms  300-500-750
 Laboratories  300-500-750
Libraries 200-300-500
Music rooms  200-300-500
 Sport halls  200-300-500
 Workshops 200-300-500
Public rooms, Village Halls, Worship Halls 200-300-500
 Concert Halls, Cinemas and theatres
 Foyer 150-200-300
Booking Office 200-300-500
Auditorium 50-100-150
Dressing Rooms 200-300-500 
Projection Rooms 100-150-200
 Body of church 100-150-200
Pulpit, Lectern 200-300-500
 Choir Stalls 200-300-500
Alter, communion table, cancel 100-150-200
Vestries  100-150-200
 Organ 200-300-500
Anesthetic Rooms-General 200-300-500
Anesthetic Rooms-Local 750-1000-1500
 Consulting Area- General 200-300-500
 Consulting Area-Examination 750-1000-1500
Corridors-General 100-150-200
Ward corridors-Day, screened from bays  150-200-300
Ward corridors- Day, open to natural light 150-200-300
Ward corridors- Morning/evening 100-150-200
Ward corridors- Night 5 to 10
Cubicles- General  200-300-500
Cubicles-Treatment 750-1000-1500
Examination- General 200-300-500
Examination- Local inspection  750-1000-1500
 Intensive therapy-Bad head 30-50
 Intensive therapy- Circulation between bed ends 50-100-150
 Intensive therapy- Observation 200-300-500
 Intensive therapy- Local observation 750-1000-1500
 Intensive therapy- Staff base(day) 200-300-500
 Intensive therapy- Staff base(night) 30
 Laboratories-General 200-300-500
 Laboratories-Examination 300-500-750
Nurses stations- Morning/day/evening 200-300-500
Nurses stations- Night desks 30
Nurses stations-Night, medical trolleys 50-100-150
Operating theatres- General 300-500-750
Operating theatres-Local  10000 to 50000
Pathology department- General 200-300-500
Pathology department-Examination 300-500-750
Pathology department- Pharmacies 200-300-500
Pathology department-Reception/ inquiry 200-300-500
Pathology department-Recovery rooms 200-300-500
 Ward circulation-Day 50-100-150
 Ward circulation-Morning/evening 50-100-150
 Ward circulation-Night 3 to 5
Ward bed head-Morning/Evening 30-50
Ward bed head- Reading  100-150-200
Night- Adult 0.1-1
Night-Pediatric 1 to 5
Night-Psychiatric 5
X-ray Areas-General 150-200-300
X-ray Areas-Diagnostic 150-200-300
X-ray Areas-Operative 200-300-500
X-ray Areas- Process dark room 50
Surgeries-General 200-300-500
Surgeries-Waiting rooms  100-150-200
Dental Surgeries- Chair Special lighting Special lighting
Dental Surgeries-Laboratories 300-500-750
Consulting rooms- General 200-300-500
Consulting rooms- Desk 300-500-750
Consulting rooms-Examination 300-500-750
Consulting rooms-Ophthalmic wall & nearvision 300-500-750
Entrance Halls 50-100-150
 Reception, cashiers and porters Desks 200-300-500
 Bars, coffee base, dinning rooms, grill, rooms, restaurants, lounges 50-200
Cloak room 50-100-150 3
Bed room 30-50-100
 Bathroom 50-100-150
General 200-300-500 1
Counters 300-500-750
 Bookshelves 100-150-200
 Reading rooms 200-300-500
 Reading tables  200-300-500
Catalogues- Card 100-150-200
Catalogues- Microfiche/visual display units 100-150-200
Reference libraries- General 200-300-500
Reference libraries-Counters 300-500-750
Reference libraries- Bookshelves  100-150-200
Reference libraries- Study tables, carrels 300-500-750
Reference libraries- Map room 200-300-500
Display and exhibition- Exhibits insensitive to light 200-300-500
Library workrooms- Book repair and binding 300-500-750
Library workrooms- Catalogue and sorting 300-500-750
Library workrooms- Remote book stores 100-150-200
Museums and Art Galleries- Exhibits insensitive to light 200-300-500
Museums and Art Galleries- Light sensitive exhibits, for e.g., oil and temper paints, undyed leather, bone, Ivory, wood, etc 150
Museums and Art Galleries-  Extremely light sensitive exhibits ,For e.g., textiles, water colors, prints and drawing, skins, botanical specimens, etc 50
Museums and Art Galleries-  Conservation studies and workshops 300-500-750
Museums and Art Galleries- Multi-purpose sports hall 300-750
Inspection of farm products where Color is important 300-500-750
Other important tasks 200-300-500
 Farm workshops
 General 50-100-150
Workbench or machine 200-300-500
 Milk premises 50-100-150
Sick Animal Pets, Calf Nurseries  30-50-100
Other Firm and Horticulture Building 20-30-50
General plant
 Turbine houses (operating floor) 150-200-300
Boiler and turbine house basements 50-100-150
Boiler house, platforms, areas around Burners 50-100-150
Switch rooms, meter rooms, oil plant Rooms, HV substations (indoor) 100-150-200
 Control room  200-300-500
 Relay and telecommunication rooms 200-300-500
Diesel generator & compressor rooms 100-150-200
Pump houses, water treatment plant Houses 100-150-200
 Battery rooms, charges, rectifiers  50-100-150
Precipitator chambers, platforms, etc  50-100-150
Cable tunnels & basements, Circulating Water culverts & screen chamber 30-50-100
 Coal Plant-Conveyors, gantries, junction towers, Unloading hoppers, ash handling plants, Setting pits, dust hoppers 50-100-150
 Coal Plant-Other areas where operators may be Attendance 100-150-200
Nuclear Plants-Gas circulation bays, reactor area, boiler Platform, reactor charges and discharge 100-150-200
Structural steel Fabrication-General 200-300-500
 Structural steel Fabrication-Marking off 300-500-750
 Sheet Metal Works- Pressing, punching, shearing, stamping, spinning, folding 300-500-750
Bench work, scribing, inspection 500-750-1000
 Machine and tool shops-Rough bench and machine work 200-300-500
 Machine and tool shops- Medium bench and machine work 300-500-750
 Machine and tool shops-Fine bench and machine work  500-750-1000
 Machine and tool shops- Gauge rooms 750-1000-1500
 Die Sinking Shops-General  300-500-750
 Die Sinking Shops-Fine Works  1000-1500-2000
 Welding and soldering shops-Gas and arc welding, rough spot welding 200-300-500
 Welding and soldering shops-Medium soldering, brazing, spot welding  300-500-750
 Welding and soldering shops- Fine soldering , fine spot welding 750-1000-1500
Assembly Shops- Rough work for example, frame and heavy machine assembly 200-300-500
Medium work, for example , office Machinery assembly 300-500-750
 Fine work, for example, office machinery assembly 500-750-1000
Very fine work, for example, instrument assembly 750-1000-1500
 Minute work for example, watch making 1000-1500-2000
Inspection and Testing Shops
Coarse Work, for example, using go/on go gauge, inspection of large sub-assembly 300-500-750
Medium work for example, inspection of painted surfaces 500-750-1000
Fine work, for example, using calibrated scales, inspection of precision mechanism 750-1000-1500
 Very fine work, for example, inspection of small intricate parts 1000-1500-2000
 Minute work, for example, inspection of very small instruments 2000
Points Shops and Spray Booths- Dipping, rough spraying 00 200-300-5
Points Shops and Spray Booths-Preparation, ordinary painting, spraying & finishing 200-500-750
 Fine painting,. Spraying and finishing  500-750-1000
Inspection, retouching and matching 750-1000-1500
 Plating shops-Vats and baths 200-300-500
 Plating shops- Buffing, polishing burnishing 300-500-750
 Plating shops- Final buffing and polishing 500-750-1000
Electrical Equipment manufacture
 Manufacture of cables & insulated wires, winding, varnishing & immersion of coils, assembly of large machines, simple assembly work 200-300-500
 Medium assembly , for example Telephones, small motors 300-500-750
 Assembly of precision components for e.g., telecommunication equipment ,adjustment, inspection and calibration 750-1000-1500
Assembly of high precision parts 1000-1500-2000
Electronic Equipment Manufacture
Printed Circuit Board
 Silk Screening 300-500-75
 Hand insertion of components, soldering 500-750-1000
 Inspection  750-1000-1500
Assembly of wiring harness, clearing Harness , testing and calibration 500-750-1000
Chassis assembly 750-1000-1500
 Inspection and testing
 Soak test 150-200-300
Safety and functional tests  200-300-500
 Slaughter houses
 General 200-300-500
 Inspection 300-500-750
Canning, Preserving and Freezing 500-750-1000
Grading and sorting of raw materials  Preparation  300-500-750
 Canned and bottled goods Retorts  200-300-500
Automatic processes 150-200-300
 Labeling and packaging 200-300-500 3
 Frozen labeling
 Process area 200-300-500
Packaging and storage 200-300-500
 Bottling, Brewing & Distilling
Keg washing and handling, bottle  Washing 150-200-300
Keg inspection 200-300-500
Process area 200-300-500
 Bottle filling 500-750-1000
Edible oils and Fats Processing
Refining and Blending 200-300-500
Production  300-500-750
Mills-milling, Filtering and Packing 200-300-500
 General 200-300-500
Hand decorating, icing 300-500-75
Chocolate and Confectionery Manufacturer
 General  200-300-500
Automatic processes 150-200-300
 Hand decoration, inspection, wrapping and packing 300-500-750
Tobacco Processing
Material preparation, making and packing 300-500-750
 Hand processes 500-750-1000
Leather Manufacture-Cleaning, tanning and stretching, vats, cutting, fleshing, stuffing 200-300-500
 Finishing, scarfing 300-500-750
 Leather Work General  200-300-500
 Pressing, glazing  300-500-750
 Cutting, splitting, scarfing, sewing 500-750-1000
Clothing Manufacture
Preparation of cloth 200-300-500
 Cutting 500-750-1000
 Matching  500-750-1000
 Sewing  750-1000-1500
 Pressing 300-500-750
 Inspection  1000-1500-2000
 Hand tailoring  1000-1500-2000
Hosiery and Knitwear Manufacture
Flat bed knitting machines 300-500-750
Circular knitting machines  500-750-1000
 Lock stitch and over locking machine 750-1000-1500
Linking or running on 750-1000-1500
 Mending, hand finishing 1000-1500-3000
 Inspection 1000-1500-2000
Glove Manufacture
Sorting & grading 500-750-1000
Pressing, knitting, cutting  300-500-750
Sewing 500-750-1000
Inspection 1000-1500-2000
 Hat Manufacture
Stiffening, braiding, refining, forming, Sizing, pounding, ironing 200-300-500
 Cleaning, flanging, finishing 300-500-750
 Sewing 500-750-1000
 Inspection 1000-1500-2000 –
Boot and Shoe Manufacture Leather and Synthetics
 Sorting and Grading 750-1000-1500
Clicking, closing  750-1000-1500
Preparatory Operations 750-1000-1500
Cutting tables and pressure 1000-1500-2000
Bottom stock preparation, lasting, Bottoming finishing, show rooms 750-1000-1500
Washing, compounding, coating, drying Varnishing, vulcanizing 200-300-500
Lining, making and finishing 300-500-750
 Work stores  100-150-200
 Unpacking, sorting 150-200-300
 Large item storage  50-100-150
 Small item rack storage 200-300-500
Issue counter, records, storemans desk 300-500-750
Warehouses and bulk stores
Storage of goods where identification requires only limited preparation of details 50-100-150
 Storage of goods where identification 100-150-200
 Automatic high bay rack stores  Gangway 20
Control station 150-200-300
 Packing and dispatch  200-300-500
 Loading bays 100-150-200
 Cold stores
 General 200-300-500
Breakdown, make-up and dispatch 200-300-500
 Loading bays 100-150-200
General Offices  300-500-750
Deep plan General offices 500-750-1000
Offices Computer Work station  300-500-750
Offices- Conference Rooms, Executive Offices 300-500-750
 Computer and data preparation Rooms 300-500-750
Filling rooms 200-300-500
Drawing Offices-General  300-500-750
Drawing Offices- Drawing Board  500-750-1000
Print rooms 200-300-500
 Counter, office area  300-500-750
Banks and building societies- Public area  200-300-500
SERVICES Workshop  Garages
(Garages)Interior parking areas 20-30-50
(Garages) General repairs, servicing, washing, polishing 200-300-500
(Garages) Workbench 300-500-750
(Garages) Spray Booths  300-500-750
 External apron-General  30-50-100
Pump area (retail details )  200-300-500
 Workshop- General 200-300-500
 Workshop- Workbench 300-500-750
 Workshop-Counter 200-300-500
 Workshop- Stores 200-300-500
Commercial laundries- Receiving, sorting, washing, drying, Ironing, dispatch, dry-cleaning, bulk Machine work 200-300-500
Commercial laundries-Head ironing, pressing, mending, spotting, inspection 300-500-750
Commercial laundries-Launderettes 200-300-500
Commercial laundries-Walkways 30-50-100
Commercial laundries-Process areas 50-100-150
Small Shops with Counters 300-500-750
Small Self Service shops with island displays 300-500-750
 (Supper-Markets) , Hyper-Markets)General  300-500-750
(Supper-Markets) , Hyper-Markets)Checkout 300-500-750
(Supper-Markets) , Hyper-Markets)Showroom for large objects, for e.g. Cars, furniture 300-500-75
(Supper-Markets) , Hyper-Markets)Shopping precincts and arcades 100-150-200

Selection of Various Types of Inverter-(Part-3)

How to select Right Inverter

  • Before buying an inverter for, It is very important to understand what is the right inverter for our requirement for that we do understand the basics criteria of Inverter.
  • In order to make a good estimate of your power needs, you’ll need to take a look at all of the devices you plan on plugging into your new inverter.
  • If we only need to use one device at a time, then that’s the only one you’ll need to look at. However, you’ll need to add together the numbers from multiple devices (like an LCD screen and a video game system) if you plan on using them at the same time.

(A) Power Requirement:

  • One of the most important factors that we must know before buying an inverter is Power requirement.
  • Power requirement means all electrical appliances (like fan, tube lights, television,Pumps, CFL etc.), we want to run at the time of power failure. The power requirement is simply addition of the power consumed by various electrical equipments.
  • The thing we must understand that Inverter is not a Generator. Inverter has its own limitations. If power requirement is more than our estimation, then an inverter alone cannot create demands effectively.
  • High power inverter can run our refrigerator and air conditioners, but battery will not last more than few hours. Hence it better to estimate Inverter Load Carefully
  • The selection of correct size Inverter is very important, If we need to power small appliances like energy efficient light bulbs, we do not need to buy a 2000W power inverter because it will consume more power even in standby mode and work very inefficiently with small appliances. On the other hand, if we connect a coffee machine to a 150W inverter we will quickly blow a fuse, Therefore power estimation is important thing.
  • The size of Inverter depends on the watts (or amps) of what we want to run. It is recommend that we choose at least 10% to 20% more than our requirement.
  • Suppose you want 1No Fans, 1No Tube lights, 1No CFL and 1No television to operate at the time of power failure. Therefore the total power requirement to be (1×90 + 1×50 + 1×25 + 1×120) = 285 watts. Here Total Load is 285 watts.

(B) Surge Power (Starting Power):

  • Starting and running power requirement of all electric appliances are different.
  • Starting power of Electrical Equipment is several times greater than their normal working power.
  • An 18 Watts CFL takes around 25 Watts power to start and after few seconds it works on 18 Watts. Some appliances like Refrigerator, Washing Machine etc take almost double power to start as compared to the normal running power.
  • For example Gridding Machine have normal working power 1000W, their starting power is higher than 4000W, so inverters with continuous power 2000W are not suitable because their peak power is limited by 4000W.
  • For selecting right Inverter, Always take into account starting power requirements of your equipment, especially devices with electric motors, Electronics Choke, Capacity, inductive
  • The Size of the inverter should be chosen based on the power consumption of your load.
  • Resistive loads: All resistive loads like toaster, coffee maker, electric range, iron, Incandescent lamps, flood lighting. Laser Printers use Nichrome resistance wire in their heating
  • The Starting Power or Surge Power rating should be 6 times the Watt rating
  • Inductive Loads: All Inductive Load like induction motor, reciprocating pumps and compressors, refrigeration, air-conditioning, Oxygen Concentrators have more starting current.
  • The Starting current (LRA) should be 5 times the full load current (FLA).
  • Capacitive Loads: Switched Mode Power Supplies (SMPS), electronic equipment like battery chargers, computers, audio and video devices, radio etc.
  • The Starting Power or Surge Power rating should be  3  times the Watt rating
  • Microwaves :
  • The Initial power consummation by the microwave will be 2 times the cooking power.
  • A Water Supply Pump:
  • The starting surge can be 3 times the normal running rating of the pump
  • The inverter should, therefore, be sized adequately to withstand the high inrush current. 

 Starting Factor

Type of Device Starting Factor
Air conditioner 5
Refrigerator / Freezer 5
Air Compressor 4
Sump Pump / Well Pump / Submersible Pump 3
Dishwasher 3
Clothes Washer 3
Microwave 2
Furnace Fan 3
Industrial Motor 3
Portable Kerosene / Diesel Fuel Heater 3
Circular Saw 3
Bench Grinder 3
Incandescent / Halogen / Quartz Lamps 3
Laser Printer / Other Devices using Quartz Lamps for heating 4
Switched Mode Power Supplies 3
Photographic Strobe / Flash Lights 4

  (C) Rating (VA rating) of the inverter:

  • It stands for the Volt ampere rating. It is the voltage and current supplied by the inverter to the equipments.
  • If an inverter operates with 100% efficiency, then the power requirement of the electrical items and power supplied by inverter is same. But 100% or ideal conditions does not exist in real.  Most inverters have the efficiency range from 60 % to 80%. This efficiency is also called power factor of an inverter and is simply  the ratio of power required by the appliances to power supplied by an inverter. Power factor of most inverters ranges from 0.6 to 0.8.
  • Rating of inverter (VA) =Power consumed by equipments (watts) / Power factor (efficiency).
  • Power of inverter (VA) = 535/0.7 = 765 VA
  • In the market 800 VA inverters are available. So Size of an inverter with 800 VA.

 (D) Type of Battery

  • The performance and Life of an inverter depends on the battery Quality.
  • Battery stores the energy needed to run appliances during power cut.
  • There are three Type of Battery
  • Lead Acid Battery
  • Tubular Battery
  • Maintenance Free Battery
  • Normally high power Lead Acid batteries are used to power inverters.

 (E) Battery Capacity (Ah):

  • Capacity of a battery is expressed in terms of Ampere Hour (Ah). It is decide the back up hours of Inverter.
  • It indicates the rate of current a battery can supply for a given duration. If the capacity of a battery is 100 Ah, that battery can supply 100 Ampere current for 1 Hour or 1 Ampere Current for 100 Hrs
  • Battery capacity = Power requirement (watts) x Back up hours (hrs) / Battery Voltage (volts) x Battery Efficiency x No of Battery
  • Example: If Inverter Load is 390 Watt, We need 3 hours back up and Battery Voltage is 12V, Battery Efficiency is 90%
  • Battery Capacity = (390 x3) / 12×0.9×1 = 109 Ah
  • Therefore a battery capacity of 120 Ah.
  • In reality battery performance degrades with usage, so you are recommended to buy 5-10% higher capacity battery.
  • Therefore a battery with a capacity of 150 Ah is suitable for our requirement.
  • If we use series – parallel battery combination for backup is
  • Backup capacity(hours) = N series X Volts X Battery Ah X N parallel / (UPS capacity in VA)
  • Where, N series = no. of batteries in series and N parallel = no. of parallel battery banks

 (F) Backup Time (Hr):

  • Backup (hours) = Battery Ah X Battery Voltage X Inverter Efficiency / Total Load (Watt)

(G) Battery Voltage (12V, 24V or 48V):

  • We can choose Battery Voltage of 12V, 24Vor 48V for inverter. The selection is very important for Voltage drop and Cable size of Inverter.
  • To control load current within limit, as load increase, we should select higher size of Battery Voltage.
  • Let’s take example.
Watt Volt Amp Cable Resistance(Ω) Voltage Drop (V)
1000 12 83 0.01 0.8
2000 24 83 0.01 0.8
4000 48 83 0.01 0.8
  • As per above table, as the load increase, by selecting higher voltage,load current within limit.
  • Let’s take example of selecting different voltage for same load (Watt)
Watt Volt Amp Cable Resistance(Ω) Voltage Drop (V)
4200 12 350 0.01 3.50
4200 24 175 0.01 1.75
4200 48 87.5 0.01 0.88
  • At Higher Load (Watt), by selecting lower voltage (12V).The load current is high. The higher the current needs the bigger the components. High currents require large diameter cables and fuses, which are expensive and the entire system is not safe.
  • By only doubling the voltage we can get double the power (Watt) at the same current.
  • 12 Volt used to be a standard for extra low voltage power systems. Today, mostly systems are 24V or 48V and include a 230V AC inverter. This means the wiring of the house does not have to be different from any other grid-connected household and cabling cost is greatly reduced.
  • The Battery Cost for higher Voltage is not more for same rating of Battery. For 12KW Load, Instead of buying a battery which has a capacity of 1000AH at 12V, (12KWH) we can rearrange the battery as a 24V 500AH (12KWH) or 48V 250AH (12KWH). The total power available from the battery is exactly the same, but with lower losses in the cabling and inverter.
  • A higher volt inverter will be more expensive than a lower volt one, and for small setups, that extra expense is unnecessary.  If we are going to have high load demands, it makes more sense to go with a higher-volt inverter for a variety of reasons. 

(H) Battery Charger:

  • The battery capacity is limited to the size of the charger. Usually, the battery capacity should be no more than 12x the maximum charge current i.e. a 5A charger can only accommodate 60AH of batteries (5 x 12 =60).
  • If discharges are expected to be less frequent than once in every 10 days, We may use formula of 20x the maximum charge current.

(I) Discharge Rate:

  • Lead acid batteries have few Amps hour if the discharge rate is fast.
  • Generally, the lead acid battery discharge rate is slow. It is 20 hours.
  • At high discharge rate, the capacity of the battery drops steeply. Suppose the battery is 10 Ah and its discharge rate is 1C. One hour discharge of the battery at the rate of 1C (10 Amps in 1 hour), the capacity reduces to 5 Ah in one hour.
  • Suppose we want to run a load at 20 Amps for 1hour. Then the capacity of the battery is 20A x 1 Hour = 20Ah.
  • Keep discharge rate to maximum 80%. Then the battery capacity should be 20Ah / 0.8 = 25 Ah
  • So a 25 Ah battery can give 20 Amps current for 1 hour to run the load.
  • But it is better to drain the battery to 50% only then, 25 Ah / 0.5 = 50 Ah.
  • Hence it is better to use a 50Ah battery to run the load at 20 Amps per Hour to keep 50% charge in the battery.
Battery Capacity Hours of Discharge
100 20
90 10
87 8
83 6
80 5
70 3
60 2
50 1



Selection of Various Types of Inverter-(Part-2)

Comparison of Inverters: 

Comparison of Different Type of  Inverter

  Square Wave Stepped  Sine Wave Pure Sine Wave
Safety of Appliances Less Moderate High
Life of Appliances Less Moderate High
Battery Life Less Moderate High
Noise Level High Moderate Normal
Heat generation High Low Normal
Suitability for appliances No Not recommended for prolonged use Yes

How to Select Batteries for Inverter

  • Batter is the vital part of inverter. Performance and life of an inverter is greatly depends upon battery.
  • There are three types of batteries available in market.
  1. Flat Plate (Lead Acid ) Battery,
  2. Tubular Battery
  3. Maintenance Free Battery.
  • Without getting too much into details, all we can say is that Tubular Batteries are the best choice for inverters. They may cost slightly more than Flat Plate, but they will last longer.
  • Maintenance Free batteries may sound good, but they have lesser life (4-5 years as compared to 7-8 years of a tubular battery).
  • But the most important thing to run batteries for a longer time is to make sure that it is topped (filled) with distilled or RO water frequently and the fluid levels are maintained.

(1) Lead Acid Battery

  • Lead acid batteries known as “Automotive Battery”.
  • Lead-acid batteries are the oldest type of rechargeable battery. Most of the inverters batteries are lead acids battery of different types.
  • It is used for automotive purpose are termed as “High Cycle” lead acid batteries.
  • These batteries are designed to provide high current for a very short duration (To start the vehicles).


  • Automotive lead acid batteries are not designed to be regularly discharged by more than 25% of their rated capacity. Here the requirement of inverter is totally different.
  • Inverter requires “Deep Cycle” type batteries to provide continuous power which can be discharged at least 50% of their rated capacity.
  • Some good deep cycle batteries can be discharged over 80% of their capacity. Deep Cycle batteries have specially designed thick plates to withstand frequent charging and discharging.
  • Lead acid batteries require regular maintenance. You have to check the electrolyte level and require to be topped up on regular intervals. These batteries release poisonous gases during charging and discharging. If you don’t keep the batteries in a properly ventilated place, it can invite serious health problems.
  • We have to keep the terminals of normal lead acid batteries corrosion free by applying petroleum jelly or grease regularly.


  • This light weighed inverter battery.
  • Price is Economical and quite cost-effective
  • This is the most common type of inverter battery.
  • It is a rechargeable and generates a large amount of current.
  • Battery life is approximately 3-4 years.  


  • We need maintain it regularly, such checking the electrolyte level, topping up with distilled water etc.
  • Need well-ventilated place while installing a lead acid inverter battery.
  • Not Safer in use.


  • Suitable for small domestic Inverter.

  (2) Tubular Battery

  • This is the most popular and efficient among all types of inverter batteries.
  • Together with robust grid design, superb efficiency, long operational life and requirement of low maintenance tubular inverter battery is the most preferable choice of all.


  • This is the most popular segment of inverter batteries used in domestic and industrial applications.


  • Long life (5 Years)
  • High electrical efficiency.
  • Less Maintenance (Less number of water toppings)


  • Cost of tubular batteries can go up to double of a normal flat plate battery


  • Suitable for both domestic and industrial Inverter.

 (3) Maintenance Free Battery

  • As the name indicates there is no need of maintaining the batteries. No need of filling distilled water at regular intervals. This is possible because of a special type of electrolyte which need not be replenished.
  • Maintenance free batteries also called as sealed batteries and do not need any regular maintenance to function impeccably.
  • Apart from that other best feature is safety. Maintenance free batteries do not emit any poisonous or harmful gases.



  • It is costlier, But the money is worth to invest.
  • It is sealed lead acid batteries which do not require topping up or additional ventilation
  • They are more durable and safer than normal lead acid inverter battery.


  • Cost is very high as compared with normal lead acid batteries.
  • Life is comparatively low (3 To 4 Years)
  • Scrap value is not much more.


 Comparison of various types of Batteries 

Comparison of various types of Batteries
  Flat Plate Batteries Tubular Batteries Maintenance Free Batteries
  1 1 - Copy 1 - Copy (2)
Cost Low High High
Safety Low Low High
Efficiency Low High Medium
Maintenance High Medium Low
Water toppings High Medium Low
Releases harmful gases Yes Yes No
Ventilation requirement Yes Yes No
Scrap Value High High Low
Weight Low High Depend on the model.
Battery Life Span Low (  3 Yrs) High( 5 Yrs) Medium (3 to 4 Yrs)
Suitable For Low power cut areas as their designed cycle life is low.    

Selection of Various Types of Inverter-(Part-1)


  • In this modern society, electricity has vital role on the most daily activities for domestic and industrial utilization of electric power for operations.
  • An inverter is used to provide uninterrupted 220V AC supply to the load connected to its output socket. It provides constant AC supply at its output socket, even when the AC mains supply is not available.
  • There are many factors, which are affecting on selecting of the best inverter for our application

Block Diagram of Inverter:

  • Power inverter is a device that converts electrical power from DC form to AC form using electronic circuits. It is typical application is to convert battery voltage into conventional household AC voltage to use Equipments, when an AC power is not available.
  • There are two methods, in which the low voltage DC power is inserted into AC Power.
  • In First Method first is the conversion of the low voltage DC power to a high voltage DC source, an then It is the conversion of the high DC source to an AC waveform using pulse width modulation.
  • In Second method the outcome would be to first convert the low voltage DC power to AC, and then use a transformer to boost the voltage to 220 volts.
  • The widely used method in the current residential inverter is the second.
  • An Inverter not only converts the DC Voltage of battery to 220V V AC Signals but also charge the Battery when the AC mains are present.
  • The block diagram shown above is a simple depiction of the way an Inverter Works.

When the AC mains power supply is available.

  • When the Utility Company AC mains supply is available.
  • C Main Sensor: the AC sensor senses it and the 230V A.C supply feeds to the Relay and battery charger.
  • Relay or Change over Switch: AC main sensor activates a relay and this relay will directly pass the 230V AC mains supply to the Load.
  • Battery Charger: Battery Charger converts line A.C Voltage to DC Voltage and Charges the Battery even when A.C Power is available.
  • Battery: Battery is charged and it is stopped when it is full charged.

 When the AC mains power supply is not available.

  • When the AC mains power supply is not available.
  • Relay or Change over Switch: AC main sensor activates a relay and this relay will connected to battery in absent of the AC mains supply.
  • Battery: Battery is providing DC Power to Oscillator circuit through Relay.
  • Oscillator Circuit: An oscillator circuit inside the inverter use pulse width modulator to generate the 50Hz frequency required to generate AC supply by the inverter.
  • The battery DC supply is connected to the Oscillator. The flip-flop converts the incoming signal into signals with changing polarity such that in a two-signal with changing polarity.
  • The first is positive while the second is negative and vice versa. This process is repeated 50times per second to give an alternating signal with 50Hz frequency. This alternating signal is known as “MOS Drive Signal “.
  • Driver Circuit: The MOS drive signals are given to the base of driver transistor which separated into two different channels.
  • Amplifier Circuit: The transistors amplify the 50Hz MOS drive signal at their base to a sufficient level and output them from the emitter.
  • Inverter Transformer: The transformer used for this is a center-tapping which divides the primary into two equal sections.
  • This center-tapping is connected to the positive terminal of the battery. Two ends of the primary are connected to the negative terminal of the battery through switches S1 and S2.
  • MOSFETs or Transistors are used for the switching operation. These MOSFETs or Transistors are connected to the primary winding of the inverter transformer.
  • When these switching devices receive the MOS drive signal from the driver circuit, they start switching between ON & OFF states at a rate of 50 Hz. This switching action of the MOSFETs or Transistors creates a 50Hz current to the primary of the inverter transformer. This results in a 220V AC or 2300V AC (depending on the winding ratio of the inverter transformer) at the secondary or the inverter transformer. This secondary voltage is made available at the output socket of the inverter by a changeover relay.

 Type of Inverter

  • The inverters are classified by depending on their output
  • Sine wave
  • Modified sine wave
  • Square wave.

(1) Sine Wave Inverter:

  • In utility Company Sine wave generated by rotating AC machinery and sine waves is a natural product of rotating AC machinery.
  • Pure sine wave inverters provide an output same as a sine wave which is similar to the utility supplied grid power, hence Pure Sine Wave inverter produces a better and cleaner current

  • All commercial instruments are designed to run on pure sine wave. Characteristics of such devices are greatly depending upon the input wave shape. A change in wave shape will affect the performance and efficiency of the appliances.
  • Sine Wave guarantees by Sine way Inverter is pure so the equipment will work to its full specifications as per its design. Appliances like Motors, refrigerators, Ovens etc will generate full power on pure sine wave input only.
  • A few appliances, such as Toaster, light dimmers, and some battery chargers require a sine wave to work propellerly. Operation of these appliances in Square or stepped waves will considerably affect the life of such equipment due to the generation of heat.
  • Distortion in the sine wave creates humming noise in transformers, and audio devices
  • Some time we noticed that audio amplifiers, Televisions, Fluorescent lamps etc make noise on inverter power. This indicates that inverter output is not pure sine wave.
  • It is always advisable and recommended to go for a pure sine wave inverter for the safety and effective performance of your appliances.


  • Output voltage wave form is pure sine wave with very low harmonic distortion and clean power like utility-supplied electricity.
  • Inductive loads like microwave ovens and motors run faster, quieter and cooler.
  • Reduces audible and electrical noise in fans, fluorescent lights, audio amplifiers, TV, Game consoles, Fax, and answering machines.
  • This type of inverters will save your current bill compared to square wave inverters.
  • Prevents crashes in computers, weird print out, and glitches and noise in monitors.
  • Back up time will be better than square wave inverters.


  • Sine wave inverters are 2 to 3 times expensive compared to square wave and modified sine wave inverters.


  • More sensitive electrical or electronic items
  • Desktop computers, laptops, Laser printers, photocopiers,
  • Camera battery chargers, cell phone chargers,
  • Mixer,
  • Fluorescent lights with electronic ballasts ,
  • Digital clocks ,
  • Sewing machines with speed/microprocessor control ,
  • Medical equipment,
  • Small house hold water pumping motors, Drives etc.

(2) Modified Sine Wave:

  • A modified sine wave inverter has a waveform like a square wave, but with an extra step.
  • Modified sine wave is a simulation of the pure sine wave output when the inverter sharply drops or increases voltage to switch polarity. As a result, the output form closely matches pure sine wave but still has much greater distortions.
  • A modified sine wave inverter will work fine with most equipment, although the efficiency or power will be reduced with some.

  • The devices are usually about 70% efficient, so we can expect some significant power losses if we are using a modified sine wave inverter in your system.
  • Motors, such as refrigerator motor, pumps, fans etc will use more power from the inverter due to lower efficiency. Most motors will use about 20% more power.
  • Some fluorescent lights will not operate quite as bright, and some may buzz or make annoying humming noises.
  • Because the modified sine wave is noisier and rougher than a pure sine wave, clocks and timers may run faster or not work at all. They also have some parts of the wave that are not 50 Hz, which can make clocks run fast. Items such as bread makers and light dimmers may not work at all in many cases appliances that use electronic temperature controls will not control. The most common is on such things as variable speed drills will only have two speeds on and off.
  • The difference between Sine wave and modified Sine wave inverter is the cost. Sine wave is considerably more expensive. We can find it practical way from it .We can install a small Pure Sine Wave inverter for any “special need” and also a larger Modified Sine Wave inverter for the rest of our applications.


  • Cheaper than pure sine wave inverters
  • Output correction waveform; relatively stable; suitable for ordinary personal users with TV, fan, lamp, computer, hot pot etc.
  • Output wave form have a very low harmonic distortion compare to Square wave inverter


  • Lower efficiency than pure sine wave inverters.
  • Power Loss is more compared to sine wave inverter.
  • Modified Sine Wave output is not suitable for continuous long time operation of certain appliances with capacitive and electromagnetic devices such as a fridge, microwave oven and most kinds of motors, printers as well as capacitive fluorescent lights etc
  • Some fans with synchronous motors may slightly increase in speed (RPM) when powered by a modified sine wave inverter. This is not harmful to the fan or to the inverter.
  • Certain rechargers for small nickel-cadmium batteries can be damaged if plugged into a modified sine wave inverter


  • Some household appliances and power tools.
  • Inductive loads like micro ovens and motors.
  • Fans and fluorescent lights,
  • Audio amplifiers, TVs, game consoles, fax and answering machines.

 (3) Square Wave Inverter:

  • The Output wave form of the Inverter is like square.
  • This is old-fashioned and the cheapest inverters, but the hardest to use.
  • A square wave inverter will run simple things like tools with universal motors without a problem, but not much else.

  • The current we get from grid is neither square wave nor pure sine wave, it’s nearly sine wave. So, our electronic devices like fan and tube light will emit some buzz noise while operating in square wave current. In some rare cases, these square wave inverters have spoiled the speed control dimmers of ceiling fans.
  • In the form of square wave, The load voltage must be switched majorly from high voltage  to low Voltage, without  using  for an intermediate step of 0Volt.
  • The main reason for this fault is high voltage output. Normally, voltage output from square wave inverters is 230 volt to 290 volt, hence it is not recommended to sensitive electronic devices like computers.
  • They just flip the voltage from plus to minus creating a square waveform. They are not very efficient because the square wave has a lot of power in higher harmonics that cannot be used by many appliances. Synchronous motors, for example, use the 50Hz component and turn the rest of the frequencies into heat
  • Square wave inverters are seldom seen any more.


  • It is very cheap


  • Life of Application is less.
  • Speed control of some equipment is not possible
  • Voltage Variation is high.
  • Large 3rd and 5th harmonic components which burn power and severely cut down on the efficiency of devices


  • Low cost AC motor drives
  • Some electronic ballast for fluorescent lamps

Electrical Thumb Rules-(Part-15)


Selection of MCB

MCB curve Type of Load Residential Commercial
B curve Resistive Loads Incandescent lights Incandescent lights
Geyser  Boilers
 Heater  Heaters
Fan blower heaters Oil radiator heaters
Slight Inductive Loads Florescent Lights Florescent lights
Small motors (FHP) High pressure mercury vapor lamps
C curve Slight Inductive Loads Fans & small pumps Sodium vapor lamps
Window / Split ACs
Lights with ballasts
 General household equipment
D curve Inductive Loads Water lifting pumps Florescent lights
UPS ID & FD fans
  Small control transformers
  Medium size motors
  Refrigerators for commercial use


Type of MCB

MCB Curve Type of Load Response Tripping Application Uses
B curve Resistive loads MCBs react quickly to overloads 3 To 5 times F.L current (0.04 To 13 Sec) Domestic & Commercial applications Suitable for incandescent lighting, socket-outlet, bulbs, heaters etc. Protection of DG sets (since DG sets have low short-circuit capacity)
C curve Slightly inductive loads MCBs react more slowly, 5 To 10 times F.L current  (0.04 To 5 Sec) Commercial and Industrial applications


Highly Inductive loads such as motors, air conditioners, fluorescent lighting lights, fans & household electrical appliances.
D curve Inductive loads MCBs are slower 10 To 20 times F.L current  (0.04 To 3 Sec) Commercial and Industrial applications


Very high inrush Inductive currents, Small transformers, welding machines. UPS, small motor & pumps, x-ray machines etc. Note, however, that MCBs with Type K characteristics may provide better protection in some applications of this type.
K curve Inductive loads MCBs are slower 8 To 10 times F.L current  (0.04 To 3 Sec)   Placing them between the traditional Type C and Type D breakers. In most cases, they allow improved cable protection to be provided in circuits that include motors, capacitors and transformers, where it would previously have been necessary to use Type D devices. This enhanced protection is achieved without increasing the risk of nuisance tripping.


Selection of RCCB

Type of RCCB Sensitive Application
Type AC Sensitive to AC Currents Only Suitable for most domestic and commercial applications.
Type A Sensitive to AC Currents + Pulsating DC Currents (Produced by Rectifier, Thyristors) Used where there are a lot of “electronic” loads, such as computer equipment or lighting systems with electronic ballasts.
Type B Sensitive to AC Currents + Pulsating DC Currents+ Pure DC Currents Use in photovoltaic (PV) solar energy installations because the PV panels produce a DC Output and some types of fault can result in the leakage of DC Currents to Earth.
Type B+ Similar to Type B, but respond to ac leakage currents over a wider frequency range Type B and Type B+ devices can be used wherever a Type AC or Type A device is specified, as they provide the same functionality as these types and more.



TYPE AC Current 50Hz AC Current 50Hz To 1KHZ Pulsating Current with DC Component Multi Frequency Current Generated By 1Phase Inverter Multi Frequency Current Generated By 3Phase Inverter


Sensitivity of RCCB

RCCBs Application
30 mA personal protection domestic installation / direct contact
100 mA limited personal protection / indirect contact
300 mA building / fire protection


MCB Enclosure Size

MCB Rating (A) Min. Enclosure Size
Height Width Depth
100A 370mm 216mm 72mm
125A 310mm 180mm 83mm
225A 370mm 217mm 72mm
250A 380mm 195mm 83.5mm
300A to 400A 506mm 381mm 153mm
600A to 800A 520mm 420mm 200mm
1000A to 1200A 704mm 554mm 173mm
1600A to 3000A 1016mm 608mm 615mm


Switch Gear Protection

Switch Gear Protection Isolation Control
Over Load Short Circuit
Circuit Breaker YES YES YES YES
Contactor NO NO NO YES
Disconnector NO NO YES NO


Type of Faults

Types of Fault Reason Consequences  Protective Device to be used
Overload When Equipment tries to run beyond its rated capacity, or there is a fault in the equipment E.g. When you keep a heater on without any water in it. It can lead to reduction in life of equipment, Failure of insulation and hence damaging the equipment. MCB / RCBO
Short Circuit Insulation Failure, Shorting of the Phase to Phase or Phase and Neutral Wires. High Inrush Current, causing permanent damage to equipment and may lead to a Fire. MCB
Earth Fault Short circuit between Phase and Earth Conductor. Can result in Fire due to sparking. RCBO / RCCB
Earth Leakage Human Body Touching Live Wires. Insulation failure   RCBO / RCCB
Over Voltage Opening of Neutral Connection increase in Phase To Phase Voltage of 440V, Surge through Lighting or transients, Over voltage from Utility. Damage to sensitive Electronic Equipment. OV protection Device
Under Voltage Drop in supply voltage, starting of heavy loads Damage of Equipment, Flickering of Lights. UV relays


 MCB Type (BS EN 60898-2)

Trip Type instantaneous
Trip (< 0.1 s)
Load Type Typical Load
B 3 to 5 In (AC) Resistive Heaters, showers, cookers, socket outlets.
4 to 7 In (DC)
C 5 to 10 In (AC) Inductive Motors, general lighting circuits, power supplies.
7 to 15 In (DC)
D 10 to 20 In High Inductive Transformers, motors, discharge lighting circuits, computers


Relays for Transformer 

Capacity of Transformer Relays on HV Side Relays on LV Side Common Relays
Generator Transformer 3 Nos Non-Directional O/L Relay – – Differential Relay or
1 no Non-Directional E/L Relay Overall differential Relay
and/or standby E/F + REF Relay Over flux Relay
  Buchholz Relay
  OLTC Buchholz Relay
  PRV Relay
  OT Trip Relay
  WT Trip Relay
220 /6.6KV Station Transformer 3 Nos Non-Directional O/L Relay 3 Nos Non-Directional O/L Relay Differential Relay
1 no Non-Directional E/L Relay Over flux Relay
and/or standby E/F + REF Relay Buchholz Relay
  OLTC Buchholz Relay
  PRV Relay
  OT Trip Relay
  WT Trip Relay
132/33/11KV up to 8 MVA 3 Nos O/L Relay 2 Nos O/L Relays Buchholz Relay
1 no E/L Relay 1 no E/L Relay OLTC Buchholz Relay
    PRV Relay
    OT Trip Relay
    WT Trip Relay
132/33/11KV up to 8 MVA to 31.5 MVA 3 Nos O/L Relay 3 Nos O/L Relay Differential Relay
1 no Directional E/L Relay 1 no E/L Relay Buchholz Relay
    OLTC Buchholz Relay
    PRV Relay
    OT Trip Relay
    WT Trip Relay
132/33KV, 31.5 MVA & above 3 Nos O/L Relay 3 Nos O/L Relay Differential Relay
1 no Directional E/L Relay 1 no E/L Relay Over flux Relay
    Buchholz Relay
    OLTC Buchholz Relay
    PRV Relay
    OT Trip Relay
    WT Trip Relay
220/33 KV, 31.5MVA & 50MVA , 220/132KV, 100 MVA 3 No O/L Relay 3 Nos O/L Relay Differential Relay
1 no Directional E/L Relay 1 no Directional E/L Relay Over flux Relay
    Buchholz Relay
    OLTC Buchholz Relay
    PRV Relay
    OT Trip Relay
    WT Trip Relay
400/220KV 315MVA 3 Nos Directional O/L Relay 3 Nos Directional O/L Relay Differential Relay
1 no Directional E/L relay. 1 no Directional E/L relay. Over flux Relay
Restricted E/F relay Restricted E/F relay Buchholz Relay
3 Nos Directional O/L Relay for action   OLTC Buchholz Relay
  PRV Relay
    OT Trip Relay
    WT Trip Relay
    Over Load (Alarm) Relay


Relays for Transmission & Distribution Lines Protection

Lines to be protected Relays to be used
400 KV Transmission Line Main-I: Non switched or Numerical Distance Scheme
Main-II: Non switched or Numerical Distance Scheme
220 KV Transmission Line Main-I : Non switched distance scheme (Fed from Bus PTs)
Main-II: Switched distance scheme (Fed from line CVTs)
With a changeover facility from bus PT to line CVT and vice-versa.
132 KV Transmission Line Main Protection : Switched distance scheme (fed from bus PT).
Backup Protection: 3 Nos. directional IDMT O/L Relays and
1 No. Directional IDMT E/L relay.
33 KV lines Transmission Line Non-directional IDMT 3 O/L and 1 E/L relays.
11 KV lines Transmission Line Non-directional IDMT 2 O/L and 1 E/L relays.


Selection Chart for 3Ph Induction Motor

Motor Rating,415V,3Ph Full Load Current (A) CONTACTOR (A) OVER LOAD RELAY (A) BACK UP FUSE (A) Cable Size
DOL Starter STAR-DELTA Starter
0.75 0.52 1.6 16   1.0 To 1.6   4 1.5 1.5    
1 0.75 2 16   1.6 To 2.5   6 1.5 1.5    
2 1.5 3.5 16   3.0 To 4.5   10 1.5 1.5    
3 2.2 5 16   4.5 To 7.0   10 1.5 1.5    
5 3.7 7.5 16   6.5 To 10   16 1.5 1.5    
7.5 5.5 11 16 16 10 To 15 4.5 To 7.0 16 2.5 1.5 2.5 1.5
10 7.5 14 16 16 13 To 20 6.5 To 10 20 2.5 2.5 2.5 2.5
12.5 9.3 18 25 16 13 To 20 10 To 15 25 4 2.5 4 2.5
15 11 21 25 16 15 To 22 13 To 20 25 6 4 6 4
20 15 28 32 18 24 To 30 13 To 20 32 10 6 10 6
25 18.5 35 40 25 25 To 30 15 To 22 50 16 10 16 10
30 22.5 40 50 25 32 To 50 24 To 30 50 16 16 16 16
35 26 47 70 32 32 To 50 25 To 30 63 25 16 25 16
50 37 66 70 40 57 To 70 32 To 50 80 35 25 35 25
60 45 80 95 50 70 To 105 32 To 50 100 50 35 50 35
75 55 100 125 70 100 To 150 40 To 57 100 70 50 70 50
90 67.5 120 140 70 100 To 150 57 To 70 160 95 70 95 70
100 75 135 140 95 100 To 150 70 To 105 160 95 70 95 70
125 90 165   125   70 To 105 160     150 95
150 110 200   125   100 To 150 200     185 150


MCB Selection Chart For Motor Protection

Kw HP 1Phase 230V DOL
3Phase 400V DOL
3 Phase 400V Star Delta
Full Load Current MCB Selection Full Load Current MCB Selection Full Load Current MCB Selection MCB Selection
0.18 0.24 2.8 10 0.9 2  —  —  —
0.25 0.34 3.2 10 1.2 2  —  —  —
0.37 0.5 3.5 10 1.2 2  —  —  —
0.55 0.74 4.8 16 1.8 3  —  —  —
0.75 1.01 6.2 20 2 3  —  —  —
1.1 1.47 8.7 25 2.6 6  —  —  —
1.5 2.01 11.8 32 3.5 10  —  —  —
2.2 2.95 17.5 50 4.4 10  —  —  —
3 4.02 20 63 6.3 16 6.3 16 10
3.75 5.03 24 80 8.2 20 8.2 20 10
5.5 7.37 26 80 11.2 25 11.2 32 16
7.5 10.05 47 125 14.4 40 14.4 40 25
10 13.4  —  — 21 50 21 50 32
15 20.11  — 27 100 27 63 40
18.5 24.8  —  — 32 125 32  — 50
22 29.49  —  — 38 125 38 63
30 40.21  —  — 51 125 51  — 63



Code Type of Relay
1 Master Element
2 Time-delay Starting or Closing Relay
3 Checking or Interlocking Relay
4 Master Contactor
5 Stopping Device
6 Starting Circuit Breaker
7 Rate of Change Relay
8 Control Power Disconnecting Device
9 Reversing Device
10 Unit Sequence Switch
11 Multifunction Device
12 Over speed protection
13 Synchronous-Speed Device
14 Under speed Device
15 Speed or Frequency Matching Device
16 Data Communications Device
17 Shunting or Discharge Switch
18 Accelerating or Decelerating Device
19 Starting-to-Running Transition Contactor
20 Electrically-Operated Valve
21 Distance protection Relay
21G Ground Distance
21P Phase Distance
22 Equalizer circuit breaker
23 Temperature control device
24 Volts per hertz relay
25 Synchronizing or synchronism-check device
26 Apparatus thermal device
27 Under voltage relay
27P Phase Under voltage
27S DC under voltage relay
27TN Third Harmonic Neutral Under voltage
27TN/59N 100% Stator Earth Fault
27X Auxiliary Under voltage
27 AUX Under voltage Auxiliary Input
27/27X Bus/Line Under voltage
27/50 Accidental Generator Energization
28 Flame Detector
29 Isolating Contactor
30 Annunciator Relay
31 Separate Excitation Device
32 Directional Power Relay
32L Low Forward Power
32N Watt metric Zero-Sequence Directional
32P Directional Power
32R Reverse Power
33 Position Switch
34 Master Sequence Device
35 Brush-Operating or Slip-ring Short Circuiting Device
36 Polarity or Polarizing Voltage Device
37 Undercurrent or Under power Relay
37P Under power
38 Bearing Protective Device / Bearing Rtd
39 Mechanical Condition Monitor
40 Field Relay / Loss of Excitation
41 Field Circuit Breaker
42 Running Circuit Breaker
43 Manual Transfer or Selector Device
44 Unit Sequence Starting Relay
45 Atmospheric Condition Monitor
46 Reverse-Phase or Phase Balance Current Relay or Stator Current Unbalance
47 Phase-Sequence or Phase Balance Voltage Relay
48 Incomplete Sequence Relay / Blocked Rotor
49 Machine or Transformer Thermal Relay / Thermal Overload
49RTD RTD Biased Thermal Overload
50 Instantaneous Overcurrent Relay
50BF Breaker Failure
50DD Current Disturbance Detector
50EF End Fault Protection
50G Ground Instantaneous Overcurrent
50IG Isolated Ground Instantaneous Overcurrent
50LR Acceleration Time
50N Neutral Instantaneous Overcurrent
50NBF Neutral Instantaneous Breaker Failure
50P Phase Instantaneous Overcurrent
50SG Sensitive Ground Instantaneous Overcurrent
50SP Split Phase Instantaneous Current
50Q Negative Sequence Instantaneous Overcurrent
50/27 Accidental Energization
50/51 Instantaneous / Time-delay Overcurrent relay
50Ns/51Ns Sensitive earth-fault protection
50/74 Ct Trouble
50/87 Instantaneous Differential
51 Phase Inverse Time Overcurrent IDMT (Time delay phase overcurrent )
51G Ground Inverse Time Overcurrent
51LR AC inverse time overcurrent (locked rotor) protection relay
51N Neutral Inverse Time Overcurrent
51P Phase Time Overcurrent
51R Locked / Stalled Rotor
51V Voltage Restrained Time Overcurrent
51Q Negative Sequence Time Overcurrent
52 AC circuit breaker
52a AC circuit breaker position (contact open when circuit breaker open)
52b AC circuit breaker position (contact closed when circuit breaker open)
53 Exciter or Dc Generator Relay
54 Turning Gear Engaging Device
55 Power Factor Relay
56 Field Application Relay
57 Short-Circuiting or Grounding Device
58 Rectification Failure Relay
59 Overvoltage Relay
59B Bank Phase Overvoltage
59P Phase Overvoltage
59N Neutral Overvoltage
59NU Neutral Voltage Unbalance
59P Phase Overvoltage
59X Auxiliary Overvoltage
59Q Negative Sequence Overvoltage
60 Voltage or current balance relay
60 Voltage or Current Balance Relay
60N Neutral Current Unbalance
60P Phase Current Unbalance
61 Density Switch or Sensor
62 Time-Delay Stopping or Opening Relay
63 Pressure Switch Detector
64 Ground Protective Relay
64F Field Ground Protection
64R Rotor earth fault
64REF Restricted earth fault differential
64S Stator earth fault
64S Sub-harmonic Stator Ground Protection
64TN 100% Stator Ground
65 Governor
66 Notching or Jogging Device/Maximum Starting Rate/Starts Per Hour/Time Between Starts
67 AC Directional Overcurrent Relay
67G Ground Directional Overcurrent
67N Neutral Directional Overcurrent
67Ns Earth fault directional
67P Phase Directional Overcurrent
67SG Sensitive Ground Directional Overcurrent
67Q Negative Sequence Directional Overcurrent
68 Blocking Relay / Power Swing Blocking
69 Permissive Control Device
70 Rheostat
71 Liquid Switch
72 DC Circuit Breaker
73 Load-Resistor Contactor
74 Alarm Relay
75 Position Changing Mechanism
76 DC Overcurrent Relay
77 Telemetering Device
78 Phase Angle Measuring or Out-of-Step Protective Relay
78V Loss of Mains
79 AC Reclosing Relay / Auto Reclose
80 Liquid or Gas Flow Relay
81 Frequency Relay
81O Over Frequency
81R Rate-of-Change Frequency
81U Under Frequency
82 DC Reclosing Relay
83 Automatic Selective Control or Transfer Relay
84 Operating Mechanism
85 Pilot Communications, Carrier or Pilot-Wire Relay
86 Lock-Out Relay, Master Trip Relay
87 Differential Protective Relay
87B Bus Differential
87G Generator Differential
87GT Generator/Transformer Differential
87L Segregated Line Current Differential
87LG Ground Line Current Differential
87M Motor Differential
87O Overall Differential
87PC Phase Comparison
87RGF Restricted Ground Fault
87S Stator Differential
87S Percent Differential
87T Transformer Differential
87V Voltage Differential
88 Auxiliary Motor or Motor Generator
89 Line Switch
90 Regulating Device
91 Voltage Directional Relay
92 Voltage And Power Directional Relay
93 Field-Changing Contactor
94 Tripping or Trip-Free Relay
Abbreviation Code
AFD Arc Flash Detector
CLK Clock or Timing Source
CLP Cold Load Pickup
DDR Dynamic Disturbance Recorder
DFR Digital Fault Recorder
DME Disturbance Monitor Equipment
ENV Environmental data
HIZ High Impedance Fault Detector
HMI Human Machine Interface
HST Historian
LGC Scheme Logic
MET Substation Metering
PDC Phasor Data Concentrator
PMU Phasor Measurement Unit
PQM Power Quality Monitor
RIO Remote Input/output Device
RTD Resistance Temperature Detector
RTU Remote Terminal Unit/Data Concentrator
SER Sequence of Events Recorder
TCM Trip Circuit Monitor
LRSS  Local/Remote selector switch
VTFF  Vt Fuse Fail

Suffixes Description

_1 Positive-Sequence
_2 Negative-Sequence
A Alarm, Auxiliary Power
AC Alternating Current
AN Anode
B Bus, Battery, or Blower
BF Breaker Failure
BK Brake
BL Block (Valve)
BP Bypass
BT Bus Tie
BU Backup
C Capacitor, Condenser, Compensator, Carrier Current, Case or Compressor
CA Cathode
CH Check (Valve)
D Discharge (Valve)
DC Direct Current
DCB Directional Comparison Blocking
DCUB Directional Comparison Unblocking
DD Disturbance Detector
DUTT Direct Under reaching Transfer Trip
E Exciter
F Feeder, Field, Filament, Filter, or Fan
G Ground or Generator
GC Ground Check
H Heater or Housing
L Line or Logic
M Motor or Metering
MOC Mechanism Operated Contact
N Neutral or Network
O Over
P Phase or Pump
PC Phase Comparison
POTT  Pott: Permissive Overreaching Transfer Trip
PUTT Putt: Permissive Under reaching Transfer Trip
R Reactor, Rectifier, or Room
S Synchronizing, Secondary, Strainer, Sump, or Suction (Valve)
SOTF Switch On To Fault
T Transformer or Thyratron
TD Time Delay
TDC Time-Delay Closing Contact
TDDO Time Delayed Relay Coil Drop-Out
TDO Time-Delay Opening Contact
TDPU Time Delayed Relay Coil Pickup
THD Total Harmonic Distortion
TH Transformer (High-Voltage Side)
TL Transformer (Low-Voltage Side)
TM Telemeter
TT Transformer (Tertiary-Voltage Side)
U Under or Unit
X Auxiliary
Z Impedance


Harmonic Effects

Harmonic R Phase Y Phase B Phase Phase Rotation Sequence Harmonic Effect
Rotation Rotation Rotation
Fundamental 120° 240° R-Y-B  
3th 3×0°= 3×120°=360°=0° 3×240°=720°=0° No Rotation          (In Phase) Adds Voltages or Currents in Neutral Wire causing Heating
9th 9×0°= 9×120°=1080°=0° 9×240°=2160°=0°
15th 15×0°= 15×120°=1800°=0° 15×240°=3600°=0°
21th 21×0°= 21×120°=2520°=0° 21×240°=5040°=0°
5th 5×0°= 5×120°=600°=(600-720)=(-120°) 5×240°=1200°=(1200-2400)=(-240°) Rotate Against Fundamental (-) (B-Y-R) Motor Torque Problems
11th 11×0°= 11×120°=1320°=(1320-1400)=(-120°) 11×240°=2640°=(2880-2640)=(-240°)
17th 17×0°= 17×120°=2040°=(2040-2160)=(-120°) 17×240°=4080°=(4320-4080)=(-240°)
23th 23×0°= 23×120°=2760°=(2760-2880)=(-120°) 23×240°=5520°=(5760-5520)=(-240°)
7th 7×0°= 7×120°=840°=(840-720)=(+120°) 7×240°=1680°=(1680-1440)=(+240°) Rotate with Fundamental (+) (R-Y-B) Excessive Heating Effect
13th 13×0°= 13×120°=1560°=(1560-1440)=(+120°) 13×240°=3120°=(3120-2880)=(+240°)
19th 19×0°= 19×120°=2280°=(2280-2160)=(+120°) 19×240°=4560°=(4560-4320)=(+240°)
25th 25×0°= 25×120°=3000°=(3000-2880)=(+120°) 25×240°=6000°=(6000-5760)=(+240°)

Difference Between High Bay-Low Bay and Flood Light Fixture


  • In the lighting industry, the term “bay” means to illuminate any large area.
  • High Bay fixtures and Low Bay fixtures are used to for illumination in Buildings with higher ceilings like warehouse lighting, industrial lighting, Commercial lighting, retail lighting, and gym lighting.
  • High Bay Lighting and Low Bay Lighting are mounted at high level via a pendant, chain, or directly to a ceiling or ceiling girder.

Type of Lighting Fixture for Larger Area Illumination:

  • There are three type of lighting fixture to illuminate large open Area
  • Low Bay Lighting Fixtures
  • High Bay Lighting Fixtures
  • Flood Lights

 (1) Low Bay Light Fixture.

  • As the name says, these bay lights are often used with lower ceilings in open areas.
  • Low bay lights are designed to illuminate open areas with ceilings Between 12 foot to 20 foot.
  • Anything use over this height treat as high bays, and anything lower is very uncommon in large open area facilities, and would require a different type of light fixture.
  • The reflectors or lens for low bays also spread the light far out to maintain a desired lighting level.



  • Ware House.
  • Petrol Station.
  • Retail Store.

(2) High Bay Light Fixture.

  • As their name implies, high-bay lights are used to illuminate spaces with high ceilings. That usually means ceilings ranging from 20 feet to 45 feet.
  • These light is effective at high Ceiling Level to provide well distributed and uniform light for open areas.
  • They need specifically reflectors (for HPS / MH bulbs) or lens angles to ensure light reaches the floor evenly and reduces wasted light. Different kinds of reflectors can accomplish different kinds of illumination tasks for high-bay lights. Aluminum reflectors make light from the fixtures flow directly downward to the floor, while prismatic reflectors create a more diffused lighting useful for illuminating shelves and other elevated objects in a space.
  • High-ceiling location has more space to fill, hence a high-bay by definition is a powerful light source that can brighten up a large area.
  • High-bay lighting is provides clear, uniform lighting of what’s below it with little glare.
  • Numerous types of fixtures can be used as a high-bay lights like LED lights, induction lights, metal halide lights, and fluorescent lights.
  • For instance, LED lights offer extremely long life and energy efficiency but require a bigger initial investment, while traditional incandescent lights are less expensive to purchase initially but don’t last as long and use more energy.
  • There are several types of fixtures available for high-bay lights. Round high-bay lights, linear high-bays, architectural high-bays and grid-mount high-bays.



  • Whenever a large indoor space needs to be illuminated, high bay lighting is usually appropriate. These area is typically vast and cover a lot of vertical as well as horizontal space. This need powerful lighting to provide the appropriate Lux levels to adequately illuminate.
  • High bay lighting fixtures typically hang from the ceiling via hooks, chains or pendants, or they may be fixed to the ceiling directly (similar to troffer lights).  
  • Various industries and facilities require high bay lighting. Some of the most common are
  • Industrial facilities.
  • Manufacturing facilities.
  • School and university gymnasiums.
  • Municipal facilities like community centers or recreation centers.
  • Commercial applications like department stores.
  • Airport hangar or any large open area industrial and commercial space with relatively high ceilings

Choosing the Correct High Bay & Low Bay Fixture

  • Choosing the right High Bay fixture can make the difference between a successful lighting project or
  • A light designed for a warehouse is a totally different than a light designed for a gymnasium or a factory floor. In gymnasium or a factory floor, a light can distribute in the area evenly while in a warehouse, a light can light up the face of the shelves and on the path way between two shelves.

(A) Lumen Output of Lamps:

  • We cannot be assumed that 100% of the lamp output will be emitted from the fitting or that the light output will be constant over its operational lifetime.
  • The actual total illumination levels that can be provided by an installed commercial light fitting will depend on the Light Output Ratio:
  • As an example, an industrial or warehouse high bay light fitting with a LOR of 70%, this indicates that 30% of the lamp’s light output is lost due to the design of the fitting.
  • The light output ratio is need to be consider in commercial lighting installation because when a lamp is positioned in a light fitting (such as an industrial 400W metal halide high bay) losses of light occur within the fitting itself.

(B) Beam Angle:

  • For maximum light coverage, we need to select a beam configuration that matches the height of the high bay light.


  • The common beam angles used for high-bay lighting are 60°, 90° and 120°.
  • The narrow beam angle creates a more focused beam enabling a high lux level on the floor or the platform.
  • The wider beam angle ensures large open areas with lower roof heights receive an excellent spread of light.


Beam Angle

Beam Angle

Ceiling Height


Up to 4 meter


4 to 6 meter


6 to 8 meter


8 to12 meter


Beam Angle & Applications

Beam Angle



Spot Lights Stadium Lights


Spot Lights Stadium Lights


Residential and Architectural Lighting


Commercial and Industrial Lighting


Commercial and Industrial Lighting


Low Ceiling Gas Stations and Public Spaces


Industrial Lighting Parking Garages


Beam Angle & Fitting Type

Beam Angle

Type of Fitting

4° To 9°

Spot Light

20° To 35°

Flood Light

36° To 49°

Wide Flood Light

More than 60°

Very Wide Flood Light

(C) Glare:

  • When there is an excessive contrast between the dark areas and bright areas in the direction of viewing, then glare can occur. When there is too much light, it will cause glare.
  • Glare can happen during daytime and nighttime. Examples of where glare can occur includes moving from a shaded location into bright sunlight, and the reflection of light from a surface which is shiny.


(D) Fixtures Shape

  • Circular fixtures creates circular beams; rectangular fixtures creates rectangular beams.
  • Round LED high bays certainly have their universal application, but if we are going to illuminate a long workbenches or a production line, we may get more efficient results from a rectangular linear high bay

(3) Flood Light Fixture.

  • A floodlight is called Flood Light because it illuminate evenly a large area with high intensity of Light.
  • Flood lights are a general method for illuminating areas where a conventional mounting arrangement of Fixtures may or may not be an available and we can also change direction Light or tilt Angle.


  • The flood light have an asymmetric throw of light which can be angled into the space to be illuminate.
  • Flood light illuminate uniformly in all directions and its exposure range can be adjusted.
  • Flood Lights utilizing light bulbs of high power to illuminate a big outdoor location.
  • Flood light is able to equably shine in all directions. Besides, the shine angels could change freely and is able to generate shadow. It is most widely used to illuminate the whole area.
  • When we install floodlights, we should need to care about glare because the brightness of the fitting is high and it angled close to horizontal.
  • Flood Light is different from spot light. Its light beam is highly diffuse without direction. Therefore, its shadow is gentle and transparency.


  • Floodlights are broad beamed, high intensity lights often used to illuminate outdoor playing fields while an outdoor sports event.
  • Flood light is a good choice for lighting and decoration of construction sites, squares, parks, arts venues.
  • Flood light also use as a object Lighting.
  • Factory buildings, stadiums, golf courses, shops, hotels, subway stations, gas stations, buildings.
  • Sculptures and other indoor and outdoor applications.

Difference between High Bay and Low Bay Lighting.

  • Normally, there is a confusion between high bay light and low bay light because both looks like same and having same applications except installation height and intensity of illumination and lumen output.
  • High bay and low bay fixtures both are typically suspension mounted using chains or hooks, but they may also have the option of being surface mounted depending on the fixture.
  • Actually both are not same lights. There are some differences between them.
  • The wattage
  • The wattage or applications of both are different. The wattage and application determines whether to call them high bay or low bay.
  • If the wattage used is above 100 Watts then it is called  high bay. Those using below 100 Watts are called low bay fixtures.
  • The Mounting Height
  • The  low bay light fixtures are used in areas where the bottom of the fixture is up to 20 feet or less above the floor.
  • They are usually spread the light evenly. They also contain optical refractors which cover the lamp thereby reducing glare. Their widespread distribution improves the vertical illumination and also permits spacing as much as 2 or more times the mounting height.
  • High bay lighting fixtures, they are mostly used in areas where the bottom of the fixture is 20 feet or more above the floor.
  • They allowing for a more concentrated beam spreading with a prominent downward component. High wattage is needed so as to illuminate the space properly.


Spacing between lights



15 feet

12 feet to 15 feet
20 feet

15 feet to 18 feet

30 feet

20 feet to 25 feet


Height and lumens


10 to 15 feet

 10,000 to 15,000 lumens

15 to 20 feet

16,000 to 20,000 lumens
25 to 30 feet

 33,000 lumens


Low Bay / High Bay Lighting Fixtures


Installation height Distance Fixture To Fixture
50 Watt 3 Meter

3 To 6 Meter

90 Watt

4 Meter 6 Meter

120 To 150 Watt

5 Meter 6 To 8 Meter
200 Watt 7 Meter

9 To 10 Meter

300 Watt 8 Meter

More than 10 Meter

Difference between Spot Light and Flood Light.

  • A spotlight casts a narrow beam of light, usually no wider than 45°. This beam is more concentrated and easier to point and control.
  • A floodlight can have a beam spread of up to 120°. It can illuminate a larger amount of space with the same wattage and lumen output as a spotlight.
  • Flood Lights is generally utilized for highlighting the architectural appearance of an outstanding or historically Building.
  • By utilizing flood lights, we can boost the in-depth framework of a building.

Determining beam width:

  • The width of a light’s beam in degrees is not always helpful. It should be much easier to know the beam width in feet, from a given distance away.
  • There is a simple formula to know Beam width
  • Beam Width =Angle of Beam x 0.018 x Distance from Light Bulb
  • If we have an 80 degree floodlight, and we want to know how wide the beam will be from 10 feet away.
  • Beam Width = 80 degrees x 0.018 x 10 feet = 14.4 feet wide

LED Vs Metal Halide

LED Watt

Metal Halide Watt
20W to 50W


30W to 75W

40W to 125W


50W to 175W


60W to 225W


80W to 250W


100W to 350W


120W to 400W

150W to 500W



Electrical Thumb Rules-(Part-15).


Luminous Efficacy, Lumen Maintenance and Color Rendition (Table-8) NBC

Light Source  Wattage Efficacy (lm/W ) Average Life Maintenance Color Rendition
Incandescent lamps  15 to 200  12 to 20  500 to 1000  Fair to good  Very good
Tungsten halogen     300 to 1500  20 to 27  200 to 2000  Good to very good  Very good
Standard fluorescent lamps       20 to 80 55 to 65 5000 Fair to good  Good
Compact fluorescent lamps (CFL)       5 to 40  60 to 70 7500 Good Good to very good
Slim line fluorescent      18 to 58 57 to 67 5000  Fair to good Good
High pressure mercury vapor lamps      60 to 1000  50 to 65 5000  Very low to fair  Federate
Blended – light lamps    160 to 250  20 to 30 5000 Low to fair  Federate
High pressure sodium vapor lamps  50 to 1000  90 to 125  10000 to 15000  Fair to good  Low to good
Metal halide lamps       35 to 2000  80 to 95 4000 to 10000 Very low  Very good
Low pressure sodium       10 to 180 100 to 200 10000 to 20000 Good to very good  Poor
LED  0.5 to 2.0  60 to 100  10000 Very good  Good for white LED


Approximate Cable Current Capacity

Cable Size Current Capacity MCB Size
1.5 Sq.mm 7.5 To 16 A 8A
2.5 Sq.mm 16 To 22 A 15A
4 Sq.mm 22 To 30 A 20A
6 Sq.mm 39 To 39 A 30A
10 Sq.mm 39 To 54A 40A
16 Sq.mm 54 To 72A 60A
25 Sq.mm 72 To 93A 80A
50 Sq.mm 117 To 147A 125A
70 Sq.mm 147 To 180A 150A
95 Sq.mm 180 To 216A 200A
120 Sq.mm 216 To 250A 225A
150 Sq.mm 250 To 287A 275A
185 Sq.mm 287 To 334A 300A
240 Sq.mm 334 To 400A 350A


Requirements  for  Physical  Protection  of Underground Cables  (As per NBC)

Protective  Element Specifications
Bricks  (a) 100 mm minimum  width 
(b) 25 mm thick 
(c) sand cushioning 100  mm  and  sand  cover 100 mm 
Concrete slabs At least 50 mm thick
Plastic  slabs (polymeric cover  strips) Fiber  reinforced plastic depending on properties  and has to be matched with the protective cushioning and cover
PVC  conduit  or  PVC  pipe  or stoneware  pipe or Hume pipe The  pipe  diameter should  be  such  so  that the  cable  is  able  to easily slip down the pipe
Galvanized pipe  The  pipe  diameter should  be  such  so  that the  cable  is  able  to easily slip down the pipe
The Trench : The trench shall be back filled to cover the cable initially by 200 mm of sand fill; and then a plastic marker strip  hall be put over the full length of cable in the trench.
The Marker Signs: The marker signs shall be provided where any cable enters or leaves a building. This will identify that there is a cable located underground near the building.
 The trench shall then be completely filled. If the cables rise above ground to enter a building or other structure, a mechanical protection such as a GI pipe or PVC pipe for the cable from the trench depth to a height of 2.0 m above ground shall be provided.



Capacity  kVA Area m2 Clear Height below the Soffit of the Beam m
25 56 3.6
48 56 3.6
100 65 3.6
150 72 3.6
248 100 4.2
350 100 4.2
480 100 4.2
600 110 4.6
800 120 4.6
1010 120 6.5
1250 120 6.5
1600 150 6.5
2000 150 6.5


Low Voltage Cabling for Building (As per NBC)

Low Voltage Cable Cables/wires, such as fiber optic cable, co-axial cable, etc. These shall be laid at least at a distance of 300 mm from any power wire or cable. The distance may be reduced only by using completely closed earthed metal trucking with metal separations for various kind of cable. Special care shall be taken to ensure that the conduit runs and wiring are laid properly for low voltage signal to flow through it.
The power cable and the signal or data cable may run together under floor and near the equipment. However, separation may be required from the insulation aspect, if the signal cable is running close to an un-insulated conductor carrying power at high voltage. All types of signal cables are required to have insulation level for withstanding 2 kV impulse voltages even if they are meant for service at low voltage.
Conduit Color Scheme Power conduit=Black
Security conduit=Blue
Fire alarm conduit=Red
Low voltage conduit=Brown
UPS conduit Green


Sub Station Guideline (As per NBC)

Substation Location Location of substation in the basement should be avoided, as far as possible.
If there is only one basement in a building, the substation/switch room shall not be provided in the basement and the floor level of the substation shall not be lowest point of the basement.
Substation shall not be located immediately above or below plumbing water tanks or sewage treatment plant (STP) water tanks at the same location
Substation Door/Shutter All door openings from substation, electrical rooms, etc, should open outwards
Vertical shutters (like rolling shutters) may also be acceptable provided they are combined with a single leaf door opening outwards for exit in case of emergency
For large substation room/electrical  room  having  multiple equipment,  two  or more  doors  shall  be provided which shall be remotely located from each other
No services or ventilation shafts shall open into substation or switch room unless specific to substation or switch room
Transformer Location In case of HV panel and transformers located at different floors or at a distance more than 20 m, HV isolator shall be  provided  at transformer end
In case transformer and main MV/LV panel room are located at different floors or are at a distance more than 20 m, MV/LV isolator shall be provided at  transformer  end
In  case  of  two  transformers  (dry  type  or transformers with oil quantity less than 2 000 liter)  located  next  to  each  other without intermittent wall, the distance between the two shall  be minimum  1 500 mm  for  11  kV, minimum 2 000 mm for 22 kV and minimum 2 500 mm for 33 kV. Beyond 33 kV, two transformers shall be separated by baffle wall of 4 h fire rating.
If dry type transformer is used, it may be located adjacent to medium voltage switch gear in the form of unit type substation. In such a case, no separate room or fire barrier for the transformer is required either between transformers or between transformer and the switch gear, thereby decreasing the room space requirement; however, minimum distances as specified.
Oil Filled Equipment (Transformer / C.B) Substations with oil-filled equipment/apparatus transformers and high voltage panels shall be either located in open or in a utility building
They shall not be located in any floor other than the ground floor or the first basement of a utility building  not be located below first basement slab of utility building.
They shall have direct access from outside the building for operation and maintenance of the equipment.
It shall be separated from the adjoining buildings including the main building by at least 6 m clear distance to allow passage of fire tender between the substation/utility building and adjoining building/main building.
Substation equipment having more than 2 000 liter of oil whether located indoors in the utility building or outdoors shall have  baffle walls  of  4  h  fire  rating between apparatus.
Provision of  suitable oil soak-pit, and where use of more than 9 000 liter of oil in any one oil tank, receptacle or chamber is involved, provision shall be made for the draining away or removal of any oil which may leak or escape from the tank, receptacle or chamber containing the same
Power Supply Voltage supply  is  at  240  V  single  phase  up  to  5  kVA, 415/240 V 3-phase from 5 kVA to 100 kVA, 11 kV (or 22 kV) for loads up to 5 MVA and 33 kV or 66 kV for consumers of connected load or contract demand more than 5 MVA.
In case of connected load of 100 kVA and above, the relative advantage of high voltage three-phase supply should be considered.
In case of single point high voltage metering, energy meters shall  be  installed  in  building  premise,such a place which is readily accessible to the owner/operator of the building and the Authority. The supplier or owner of the installation shall provide at the point of commencement of supply a suitable isolating device fixed in a conspicuous position at not more than 1.7 m above the ground so as to completely isolate the supply to the building in case of emergency
Trench Drain In case of cable trench in substation/HV switch room/MV switch room, the same shall be adequately drained to ensure no water is stagnated at any time with live cables.
Fence for Substation Enclose any part of the substation which is open to the air, with a fence (earthed efficiently at both ends) or wall not less than 1800 mm (preferably not less than 2400 mm) in height
HV Distribution in Building The power supply HV cables voltage shall not be more than 12 kV and a separate dedicated and  fire  compartmented  shaft  should  be provided for carrying such high voltage cables to upper floors in a building. These shall not be mixed with any other shaft and suitable fire detection and suppression measures shall be provided throughout the length of the cable on each floor.
Switch Room / MV switch room Switch room / MV switch room shall be arrived at considering 1200 mm clearance requirement from top of the equipment to the below of the soffit of the beam .In case cable entry/exit is from above the  equipment  (transformer,  HV switchgear, MV  switchgear),  height  of substation room/HV switch room/MV switch room shall also take into account requirement of space for turning radius of cable above the equipment height.



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