Forms of Separation for Panel (PART-2)


(C) Form 3

  • This is more complicated but safer than Form 2.
  • In form 3a, each device is isolated in a compartment that protects it from the effects of any incidents that may occur on another Part / Switchgear.
  • Busbars and functional units are segregated. Functional units are also separated from each other in cubicles, and terminals are then separated from functional units, but they are not segregated from other functional units’ terminals.
  • Busbar and Switchgear: Bus bars are separated from the Switchgear units,
  • Busbar and Termination: Bus bars are not separated from any incoming or outgoing terminations.
  • Switchgear and Switchgear units: Switchgear units are separated from each other.
  • Switchgear and Termination: Switchgear units are separated from any incoming or outgoing termination.
  • Termination and Termination: Incoming and outgoing terminals are not separated from each other
  • This is further classified into 2 categories.

FORM 3A

  • External cabling terminals are not segregated from busbars.

FORM 3B

  • External cabling terminals are separated from busbars

FORM 3B TYPE 1

  • As from 3 but: Busbar separation is achieved by insulated coverings, e.g. PVC sleeving, wrapping or coating.
  • Terminals are therefore separated from the busbars, but not from each other.

FORM 3B TYPE 2

  • As form 3 but: Busbar separations is achieved by metallic or non-metallic rigid barriers or partitions.
  • Terminals are therefore separated from the busbars, but not from each other. 1

 Advantages:

  • The advantages include safety, ease of maintenance and reliability because it’s possible to isolate and perform maintenance on each starter without having to power down the whole switchboard.
  • Serious faults within a starter are also more likely to be contained within a cubicle meaning adjacent starters are unaffected and can operate normally.

Electrical Safety:

  • More reliable and safer than Form-2 due to separation between live parts (Busbar and Switchgear, Switchgear and Switchgear).

Cost:

  • All these advantages come at a cost as a Form 3 board is significantly bigger and more expensive than a Form 1 or 2 board.

Application:

  • Form 3 segregation is typically used for Big projects and larger operations that have a greater number of loads, motors and critical processes.
  • They are utilised when safety, reliability and limited downtime are crucial.

(D) Form 4

 This is the highest form rating, as specified by AS/NZS / IEC 61439.1.

  • Busbars are separated from functional units
  • Functional units are separated from each other
  • Terminations to functional units are separated from each other
  • Busbar and Switchgear: Bus bars are separated from the Switchgear units,
  • Busbar and Termination: Bus bars are separated from any incoming or outgoing terminations.
  • Switchgear and Switchgear units: Switchgear units are separated from each other.
  • Switchgear and Termination: Switchgear units are separated from any incoming or outgoing termination.
  • Termination and Termination: Incoming and outgoing terminals are separated from each other
  • This is further classified into 2 categories.

FORM 4A

  • External cabling terminals are within the same cubicle as the corresponding functional unit.

FORM 4B

  • The external cabling terminals are not in the same cubicle as the corresponding functional unit, and they are separated from the terminals of other functional units.

CLASSIFICATION OF FORM 4B

TYPE Busbar Separation Termination Location Cable Gland
FORM 4B TYPE-1 PVC sleeving, wrapping or coating. Termination is within the same compartment as the functional unit. Common Gland Plate
FORM 4B TYPE-2 Rigid Barriers Termination is within the same compartment as the functional unit. Common Gland Plate
FORM 4B TYPE-3 Rigid Barriers Termination is within the same compartment as the functional unit. Individual Gland Plate
FORM 4B TYPE-4 PVC sleeving, wrapping or coating. Terminals are external to the functional unit and separated by insulated coverings, e.g. PVC Boots Common Gland Plate
FORM 4B TYPE-5 Rigid Barriers Terminals are external to the functional unit and separated by insulated coverings, e.g. PVC Boots Common Gland Plate
FORM 4B TYPE-6 Rigid Barriers Terminals are external to the functional unit compartment and enclosed in their own compartment by means of rigid barriers or partitions Common Gland Plate
FORM 4B TYPE-7 Rigid Barriers Terminals are external to the functional unit compartment and enclosed in their own compartment by means of rigid barriers or partitions complete with integral glanding facility Individual Gland Plate

2

  • The major difference between Forms 3 and 4 is the separation of the terminals of each functional unit the terminals of other units.

Advantages:

  • The main advantage of this model is the ability to safely connect and disconnect outgoing cables while the rest of the switchboard remains in operation.
  • In Large Panel access is required for inspection, to reset an auxiliary function. If the point of isolation and termination are each in their own individual box this can be deemed safer than if all the devices and connections are behind a single door

Electrical Safety:

  • More reliable and safer than Form-4 due to separation between live parts (Busbar and Switchgear, Switchgear and Switchgear, Termination and Termination).
  • Due to internal segregation is to limit the effects on adjacent circuits if something goes wrong. An external fault should cause a device to trip but this must not have any effect on any other circuits.

Cost:

  • Form 4 board is significantly bigger and more expensive than a Form 3 board.

Applications:

  • used in hospitals or for critical industrial processes.

SUMAMRY OF FORM OF SEPERATION OF PANEL

SUMAMRY OF FORM OF SEPERATION OF PANEL

SEPERATION BETWEEN FORM-1 FORM-2 FORM-3 FORM-4
BUSBAR–SWITCHGEAR NO YES YES YES
BUSBAR–TERMIATION NO NO / YES YES YES
SWITCHGEAR—SWITCHGEAR. NO NO YES YES
SWITCHGEAR–TERMIANTION NO NO NO YES
TERMIANATION–TERMIANTION NO NO NO YES

Forms of Separation for Panel (PART-1)


Introduction:

  • Forms of segregation have great importance in electrical Panel designs.
  • Form of segregation is the rule for provide separation from a one energizes function part to other energize function pant and access to a part of the assembly while other parts may remain energized. This can be achieved by using metallic or non-metallic physical barriers or insulation.
  • The form of segregation provides protection against four objectives.
  1. Protection against direct contact with live dangerous parts of adjacent functional units.
  2. Protection against the entry of solid objects from one unit of an assembly to an adjacent unit.
  3. Limitation of the effects of the spread of electric arcs.
  4. Facilitation of panel maintenance operations.

Type of Separation:

  • As specified by AS / NZS / IEC 61439, There are four main categories outlined by the standard for internally separating the switchgear units and busbars of a Panel are
  1. Form 1 (No segregation between busbar, terminals and Switchgear units)
  2. Form 2 (Separation between switchgear units and the busbar)
  3. Form 3 (Separation are between switchgear units and the busbar and Separation between Switchgear unit to Switchgear Unit)
  4. Form 4 (Segregation between busbar, terminals and Switchgear units)
  • The complexity of the forms increases with the numbers.

1

(A) Form 1:

  • A Form 1 Panel has no internal separation among busbar, switchgear and outgoing Cable Terminations.
  • All functional units are installed in one central section to provide protection against contact with any internal live parts.
  • Busbar and Switchgear: Bus bars are not separated from the Switchgear units,
  • Busbar and Termination: Bus bars are not separated from any incoming or outgoing terminations.
  • Switchgear and Switchgear units: Switchgear units are not separated from each other.
  • Switchgear and Termination: Switchgear units are not separated from any incoming or outgoing termination.
  • Termination and Termination: Incoming and outgoing terminals are not separated from each other

2

Advantage:

  • Simple Design and Less Space Required.

Electrical Safety:

  • Less due to No separation between live parts.
  • This form construction is rarely used.

Cost:

  • Less Cost

Application:

  • For small, low power switchboards.

(B) Form 2

  • Form 2a is the simplest for protecting against accidental contact with any internal live parts or components like the busbars, which are considered to be the most dangerous components.
  • In FORM-2, Busbar is Separate from the Switchgear units but may or may not be separate from Cable terminal.
  • Busbar and Switchgear: Bus bars are separated from the Switchgear units,
  • Busbar and Termination: Bus bars may or may not separate from any incoming or outgoing terminations.
  • Switchgear and Switchgear units: Switchgear units are not separated from each other.
  • Switchgear and Termination: Switchgear units are not separated from any incoming or outgoing termination.
  • Termination and Termination: Incoming and outgoing terminals are not separated from each other
  • This is further classified into 2 categories.

FORM 2A

  • Terminals are not separated from the busbars or each other.

FORM 2B

  • Terminals are separated from the busbars

FORM 2B TYPE 1

  • As form 2 but Busbar separation is achieved by insulated coverings, e.g. PVC sleeving, wrapping or coating.
  • Terminals are the therefore separated from the busbars, but not from functional units or each other.

FORM 2B TYPE 2

  • As from 2 but Busbar separation is achieved by metallic or non-metallic rigid barriers or partitions
  • Terminals are therefore separated from the busbars, but not from functional units or each other

3

Advantages:

  • There are several advantages to segregating functional units and busbars.
  • This model allows circuit breakers to be reset when the switchboard is live because the operator is not exposed to a live busbar.

Electrical Safety:

  • More than Form-1 due to separation between live parts (Busbar and Switchgear).

Cost:

  • More Costly than Form-1

Application:

  • For small, low power switchboards.

Measurement of LUX Level and Uniformity at Indoor and Outdoor Lighting (Part-3)


(3) Grid Method to measure illumination on the road

  • The arrangement of the measuring points depends on the distance between the Illumination Pole and the width of the Road.
  • The measurement of illuminance should be performed on the area in longitudinal direction two consecutive luminaires in the same row and in transverse direction the width of the area with the same illumination class, i.e. if the road and adjacent pavement or bicycle path have the same illumination class, they may be considered as one area during the measurements. The measuring points should be distributed evenly within the measuring field.
  • The distance between the measuring points (D in Meter) in the longitudinal direction should be calculated using the formula
  • The distance between the measuring point in longitude ( D)=S / N
  • where:
    S= the distance between the luminaires in [m],
    N= the number of measurement points in the longitudinal direction,
    for S ≤ 30 m, it is N = 10,
    for S > 30 m, the smallest integer giving D ≤ 3 m.
  • The distance between measurement points (d in Meter) in the transverse direction should be calculated with the formula:
  • The distance between the measuring point in transverse (d) = Wr / n
  • where: Wr= the width of the road or the area under consideration in Meter.
  • n = the number of measurement points in the transverse direction equal to 3 or more and being an integer giving d ≤ 1.5 m.
  • The distance between the points and the edges of the surface under consideration should be D/2 in the longitudinal direction and d/2 in the transverse direction. The location of the measurement points in the measuring field is shown in Figure.

1

(4) Equal Space Method

  • In this Method at least10 equal measuring Points are taken between two lighting Pole on one side of the Roadway.
  • These measurement points cannot be spaced more than 5 meters apart. Two lines of measurement points are needed per driving lane, one-half lane width apart.
  • Once you have taken all of your illuminance measurements, you can calculate an average illuminance for the section of roadway you have measured.

2

What is Lighting Uniformity

  • light uniformity refers to the uniformity of lighting in an environment. It is necessary to maintain the uniformity of light in order to make sure that everything is perfectly visible in the room.
  • Uniformity is the ratio of the minimum lighting level to the average lighting level in a specified area.
  • U1 = E Min / E Average
  • U2 = E Min / E Maximum
  • U & E stands for uniformity & illuminance respectively.
  • Uniformity is a quality parameter for the overall illuminance distribution.
  • It is quite useful to use this uniformity ratio to describe how the lights are evenly distributed on the ground. If the difference between minimum and average lux is small, then the ratio is high, which gives better light uniformity.
  • The maximum lighting uniformity is 1, which means the lux levels in all the sampling points are the same. However, it is very unlikely to achieve this maximum value for artificial lighting.
  • If the uniformity is very low for the outdoor or indoor lighting, the citizens, workers, or athletes might feel uncomfortable, and thus their vision is affected.
  • The more uniform the light distribution, the better the illuminance and the more comfortable the visual experience.  The closer the illuminance uniformity is to 1, the better, otherwise the smaller the more visual fatigue.

How to improve Lighting Uniformity

  • Adjust the aiming angle of the floodlight,
  • The lights irradiated by the floodlights should overlap each other,
  • Use pole lights, high-power floodlights, street lights, etc. to supplement lighting.

Light Uniformity Standard

  • There are different light uniformity standards that need to be followed depending on the nature of the environment
  • Most focus-intensive tasks require a uniformity index of around 0.6, whereas, technical drawing and other demanding tasks require a ratio of at least 0.7.
  • Uniformity value greater than 0,60 is recommended in working areas. Because, above this level, the change in light levels cannot be sensed by people and that makes them comfortable. Proper lighting of the environment also helps employees work more comfortably when looking at the computer screen.
  • Due to low uniformity in road lighting, the homogeneity of lighting will be distorted. So, very bright and very dark spots will occur on the road. If brightness changed very often, this will cause eye strain and stresses the drivers
  • In order to avoid these situations, average uniformity value greater than 0.35 or 0.4 is required according to road lighting class.
Standard Area Ratio of Minimum/Average Illumination
UK CIBSE and German DIN guidelines The general lighting scheme 0.6 and 0.8
NBC-2005, page no 759 Working Area Not Less than 0.7

Table-6: Recommended Levels of Illumination (BIS, 1981)

Type of Road Road Characteristics Ratio of Minimum/Average Illumination
A-1 Important traffic routes carrying fast traffic

0.4

A-2 Main roads carrying mixed traffic like city main roads/streets, arterial roads, throughways

0.4

B-1

Secondary roads with considerable traffic like local traffic routes, shopping streets

0.3

B-2 Secondary roads with light traffic

0.3

EUROPEAN STANDARD- EN 12464-1:2011

Space

 Uniformity U0 (Emin / Em

Areas with traffic and corridors

0.4
Stairways, escalators, and travelators

0.4

Lifts

0.4
Loading bays

0.4

Coffee-break rooms

0.4
Technical facilities

0.4

Storage spaces

0.4
Electronics workshops, testing, and adjustments

0.7

Ball-mill areas and pulp plants

0.4
Offices and writing

0.6

Check-out areas

0.6
Waiting rooms

0.4

Kitchens

0.6

Parking areas

0.4
Classrooms

0.6

Auditoriums

0.6

EUROPEAN STANDARD- EN 12464-1:2011

Task illuminance ≥ 0.7
Illuminance of immediate surrounding areas ≥ 0.5

Football Field Lighting Design

Nature of the Sports Field Required U1 Light Uniformity
Class I such as for a National Competition ≥ 0.7
Class II such as for a League ≥ 0.6
Class III such as for a Training Ball Field ≥ 0.5

Industrial and Commercial Lighting Uniformity Requirement

The Area The Light Uniformity Standard
Highway 0.4-0.6
Sports field 0.5-0.8
Office 0.4-0.6
Parking Lot 0.4-0.5
Warehouse 0.4-0.6
Running Track 0.3-0.5
Airport 0.2-0.3

Measurement of LUX Level and Uniformity at Indoor and Outdoor Lighting (Part-2)


(3) AS per Deutsch Norm DIN 5035

  • In this Method the working plane divide into a number of sections which are at least rectangular, of ratio of length to side not less than 1: 2 but which are preferably of square shape.
  • A square grid of minimum size 1 meter is established within each section with a measurement point at the centre of each square.
  • The grid module defining the measurement points is selected so as not to coincide with the luminaire grid in either principal direction.
  • In exceptionally large interiors the grid size may be up to 5 meters. there is not any mention of accuracy limits of the method, but this is not surprising given the flexibility which the user of the method is allowed in choice of grid size.
  • The DIN system is the only one of the three methods studied to give any advice concerning illuminance measurements in obstructed interiors. Areas of the working plane located between large obstructions are treated for measurement purposes as separate spaces.

1

OUTDOOR ILLUMINATION (LUX LEVEL) MEASUREMENT

 (1) Nine Point Method for Determining Lux Levels in Street Lighting

  •  The Lux Level of Street Light is measured by 9-point method.
  • We need to make two equal quadrants between two light poles and between Pole and Rode edge.
  • Two Measuring Points below Light Pole (A1,A2)  and Two opposite side of Pole at Road Edge (A3,A4).
  • Two Point between Pole and Road edge (B1,B3).
  • One Point Between Pole  (B2) and on One Point between opposite side of Pole at road edge (B4)
  • One Point is at centre (C1).
  • Average Lux = (A1+A2+A3+A4)/16 + (B1+B2+B3+B4)/8 +C1/4

2

  • Solution
26 Lux 27 Lux 13 Lux
12 Lux 15 Lux 14 Lux
26 Lux 32 Lux 22 Lux
  • Average Lux = (A1+A2+A3+A4)/16 + (B1+B2+B3+B4)/8 +C1/4
  • Average Lux = (26+26+13+22)/16 + (12+27+14+32)/8 +15/4
  • Average Lux =20Lux 
MIN 12 Lux
MAX 32 Lux
AVG 20 Lux
U1=MIN/AVG 0.58
U2=MIN/MAX 0.38

 (2) As per Grid Point Set Up Measurement

  • Identify a horizontal grid of measurement points on the Illumination Measurement site surface. Locate measurement points on gridlines covering the test measurement area.
  • Ensure that the spacing between measurement points is uniform in both directions and is less than one-half the pole height or less than 4.5 Meter, whichever is smaller.
  • For installations with lights spaced less than 4.5 Meter apart, locate measurement points no farther apart that one-half the pole height, with at least three points between poles in both directions.
  • Record the location of all measurement grids and point layouts with dimensions from surrounding poles or other structures. Provide this information, including a sketch or rendering of the grid layouts.
  • For open areas such as main parking, make the measurement grid large enough to cover at least four poles of this Area layout and at least two Pole are covered.
  • For site perimeter open areas or areas adjacent to a building edge establish the test area measurement grid in a typical perimeter or building edge area. The depth of the test area should extend from the paved site boundary or building edge inward to the nearest line of light poles that are at least 4.5 Meter from the boundary or building edge.
  • The width of the test area must cover at least two of the poles in the line that is at least 4.5 Meter from the boundary or building edge.

(A) In Open Area

3

(B) In the Area of Site Perimeter

4

(C) Near Site Boundary Area:

5

Measurement of LUX Level and Uniformity at Indoor and Outdoor Lighting (Part-1)


Introduction:

  • Working plane illuminance (Lux Level) need to be measured in the field for cross check of whether the existing installation meets a design requirement or not.
  • Field surveys may also be useful to identifying the causes of complaints about lighting, hence the results of field surveys may be useful for the designer, installers and end users.
  • There are various methods are developed for field measurement of Interior Lighting and External Lighting.
  • The Measurement Methods recommended by the various national lighting bodies are generally similar or slightly derivatives to each other. The most common method / Standard is BEE, CIBSE, IES and DIN code
  • The most of methods require to measurement of illuminance at points on a grid at working-plane height or at Floor, but the grid size and position of the measuring points may be differed from various standard to standard.
  • The IES method and its derivatives use the position of the grid according to the luminaire locations.
  • The CIBSE and DIN methods use a position of grid according to the room size.
  • The techniques of analysis of the field measurement results also differ

Basic Requirements for Exterior & Interior Light Level Measurement

  •  The following Points should be considered for accurate measurement of interior and exterior lighting Lux level.
  • Where possible, use the same calibrated illuminance measurement meter (LUX Meter) If the same meter is not available, use the same make and model of calibrated meter to minimize error.
  • When taking measurements, verify that any objects/materials are not blocking any light to the meter head. The use of a remote meter head cabled to the meter body is recommended to prevent the operator from blocking the meter’s “view” of the lighting system being measured.
  • In Outdoor Lighting it is essential to measure of illuminance should be done in night (proper dark).
  • For indoor lighting, measurements with lights ON and Lights OFF technique can be followed and the daylight variation is not too much and the survey time is not too long.
  • In an installation of fluorescent discharge lamps, the lamps must be switched on at least 30 minutes before the measurement to allow for the lamps to be completely warmed up.
  • In many situations, the measuring plane may not be specified or even non-existent. Hence it is necessary to define measurement height, typically 0.8 to 1 meter from the ground or floor level.
  • The lux measurement procedure simply requires positioning a meter’s sensor on the surface or location where you wish to measure the incident light.
  • The sensor should face the light source at a right angle. If the sensor is not perpendicular to the light, the measurement will be incorrect, though some lux meters have a cosine correction to account for the angle.
  • Meters that require a colour correction factor may have a means of inputting the CCF to adjust the result for LEDs or fluorescent lights; otherwise, you will have to manually multiply the measured lux by the CCF.

 INDOOR ILLUMINATION (LUX LEVEL) MEASUREMENT.

 (1) As per Room Index Method (as per BEE Code / CIBSE Code):

  •  This methos is more suitable where measuring Plan / Points for an interior is more rectangular than square. First, we need to be found Room Index.
  • Based on the room index, the minimum number of illuminance measurement points is decided by Room Index Number
  • Room Index (RI) = (L x W) / H x (L+ W)
  • Where L = Length of Room
  • W = Width of Room
  • H= Height of the luminaires above the plane of measurement 

Table 4-2: Number of points for measuring illuminance

Room index

Minimum number of measurement points

 

For ± 5% accuracy

For ± 10% accuracy

RI < 1

8

4

1 < RI < 2

18

9

2 < RI < 3

32

16

RI > 3

50

25

 Sample calculation

  • Measure Illumination Level of an office room have length, L = 7.5 m and width W = 5 m,
  • Solution:
  • Suppose Height of Illumination from Floor is 2 Meter
  • Room Index RI = (L x W) / H x (L+ W)
  • Room Index RI = (7.5 x 5) / 2 x (7.5+ 5)
  • Room Index RI = 1.5
  • From Table 4.2 minimum Illumination Measure Points should be 18 No’s
  • The illuminance measurements Points with Measured Value in Lux are marked on the grid.  

1

Measurement Reading Details

107 Lux

99 Lux

85 Lux

65 Lux

65 Lux

45 Lux

73 Lux

130 Lux

105 Lux

110 Lux

86 Lux

87 Lux

59 Lux

50 Lux

58 Lux

99 Lux

75 Lux

106 Lux

115 Lux

76 Lux

         

Min

45 Lux

     

Max

130 Lux

     

Average

85 Lux

     
         

U1=MIN/AVG

0.5 Lux

     

U2=MIN/MAX

0.3 Lux

     

 

 (2) As per Point Layout Method

  • For office and other task areas, identify a set of measurements points on desktops and other work surfaces that best represents lighting conditions in the space.
  • It may not be possible to develop a uniform spacing grid, but points should be chosen that represent the various lighting conditions across the space.
  • For each separate horizontal grid, identify a vertical plane representative of the lighting in the area (typically the gridline directly between two light fixtures).
  • On this vertical plane, set a grid (line) of points at 1.5 Meter above the site surface at each of the corresponding horizontal measurement points.
  • The following figures provide sample layouts for selecting horizontal measurement points for typical areas where lighting measurements are taken

2

Measurement Reading Details

107 Lux

80 Lux

100 Lux

75 Lux

100 Lux

65 Lux

73 Lux

70 Lux

75 Lux

60 Lux

99 Lux

87 Lux

95 Lux

58 Lux

98 Lux

60 Lux

65 Lux

63 Lux

66 Lux

78 Lux

75 Lux

78 Lux

62 Lux

99 Lux

87 Lux

95 Lux

58 Lux

98 Lux

         

Min

58 Lux

     

Max

107 Lux

     

Average

80 Lux

     
         

U0 or U1=MIN/AVG

0.7 Lux

     

Ul or U2=MIN/MAX

0.5 Lux

     

Typical Earthing Resistance Value


  • The resistance offered by the earth electrode to the flow of current into the ground is known as the earth resistance or resistance to earth.
  • Ideally a ground resistance should be of zero ohms but It is always greater than Zero .System ground resistances can be reduce by the use of a number of individual electrodes connected together.
  • Total earthing resistance is the sum of the resistance of earth lead wires, Contact resistance between the surface of the earth electrode and the soil and The resistance of the body of the soil surrounding the earth electrode.
  • The value of earthing resistance varies on the Type of Soil, Soil characteristic, soil resistivity and the climatic condition. Moisture content in soil plays a vital role in the soil resistivity. value of individual earthing pit resistance is not so important. Different codes specifies the required value of earthing system.
  • Electrical Systems can work with earth resistance of 20 ohms, though generally 10 ohms is the specified Maximum limit.
  • But communication systems need very stringent limit, typically one ohm. This is because the higher the ground resistance, higher would be noise interference in the systems.

USAID

a) Power stations (generating station)

0.5 ohms

b) EHT Sub-station

1.0 ohms

c) 33 KV Stations

2.0 ohms

d) D/t Structure

5.0 ohms

e) Tower Foot resistance

10.0 ohms

IEEE STANDARD 142

Chapter: 4.1.3 , page 164
For industrial plant substations and buildings and large commercial installations.

1Ω to 5 Ω

Resistances of less than 1 ohm may be obtained using a number of individual electrodes connected together. Such a low resistance is only required for large substations, transmission lines, or generating stations.

National Electric code (NEC) 2011, (IS SP30 Chapter 14 -India)

Chapter: 3.0.9
unless otherwise specified ,It is recommended that the value of any earth system resistance shall not be more than

IS 3043 (India)

Chapter: 22.2.3
The continuity resistance of the earth return path through the earth grid should be maintained as low as possible and in no case greater than

This applicable for main earth grid connected with the transformer/return path

Oil Industry Safety Directorate Government of India (OISD STANDARD – 137)

Chapter: (7. ii. b) Allowable earth-Resistance Values
Allowable earth-Resistance Values The resistance value of an earthing system to general mass of the earth should not exceed.
For electrical systems and metallic structures.

4Ω

For storage tanks.

7Ω

for main earth grid, and bonding connections between joints in pipelines and associated facilities.

1Ω

for each electrode to the general mass of the earth

2Ω

IS 2309 (india) / BS 7430:1998

Clause:12.3.1 Page 32,Resistance to Earth
Lightning arrestors ground resistance for  Protection of buildings and allied structures is

10Ω

An earth electrode should be connected to each down conductor. Each of these earths should have a resistance not exceeding the product given by 10 a multiplied by the number of earth electrodes to be provided.
The whole of the lightning protective system, including any ring earth, should have a combined resistance to earth not exceeding 10 Ω without taking account of any bonding.
If the value obtained for the whole of the lightning protective systems exceeds 10 Ω, a reduction can be achieved by extending or adding to the electrodes or by interconnecting the individual earth terminations of the down conductors by a conductor installed below ground, sometimes referred to as a ring conductor

IS 2689:1989

Table 4 page 28 (Reaffirmed March 2010)
Lightning arrestors ground resistance for Protection  of buildings and allied structures is

10Ω

NEC 250.56

Clause: 250.53 Grounding Electrode System Installation.
The maximum resistance for a single electrode consisting of a rod, pipe, or plate.

25Ω

If a higher resistance is obtained for a single electrode, a second electrode of any of the types specified in the NEC is required.
This should not be interpreted to mean that 25 ohm is a satisfactory resistance value for a grounding system.

IEEE Std 80-2000 (Revision of IEEE Std 80-1986)

the evaluation of ground resistance for the most transmission and other large substations, the ground resistance is usually about

1Ω or less

In smaller distribution substations, the usually acceptable range is

1Ω to 5Ω

NFC 17-102, July 1995

that the resistance value measured using conventional equipment should be

1Ω or less

This resistance should be measured on the earthing termination insulated from any other conductive component.

IEC 62305-1

edition 2.0 – 2010-12
the conventional earthing impedance related to the earth termination system is (*for the soil resistivity less than or equal to 100 Ω)

4 Ω

Ministry of Railways- Government of India

 
The acceptable Earth Resistance at earth MEEB bus bar shall not be more than

1Ω

For achieving this value more than one earth pits can be installed if necessary depending upon the soil resistivity. In places where space is not available to provide parallel earth pits then longer earth rods may be provided.
The longer earth rods thus provided should be in multiples of three meters.
The combined resistance of the earthing system shall be not more than the following values
Traction substation

0.5Ω

Switching station

2Ω

Booster transformer station

10Ω

Auxiliary transformer station

10Ω

Maximum values of earth resistances specified for earthing of Signaling and Telecommunication equipment’s are as under
Telegraph and Block Instrument using earth return circuit 10 Ω
Earths for surge arrestors/ lightening dischargers

10Ω

Earthing of Signalling equipment

10Ω

Earthing of signalling cable screen in AC electrified areas

10Ω

Earthing of Telephone Exchange

Earthing of aluminum sheathed telecom cable in AC electrified area

Earthing of equipment in VF repeater stations and cable huts.

Axle counter cable screened in AC electrified area

Electronic Interlocking installation

Integrated Power Supply System & its individual modules

Digital Axle Counter EJB and its apparatus case connected to same earth All cable armors connected to same earth.

Reset box of Digital Axle Counter connected to earth (indoor) near SM’s Room.

Railway Vikas Nigam Limited

RVNL/Elect/GS/11
The earth continuity test of metallic envelopes shall be done for electrical continuity. Electrical resistance of the same, along with the earthing lead, excluding any added resistance of earth leakage circuit breaker, measured from the connection with the earth electrode to any point in the earth conductor in the completed installation, shall not exceed

No earth electrode shall have resistance greater than

In rocky soil, the resistance may be up to

Locations having more than one electrode shall be connected in parallel to reduce the resistance.

MANUAL OF STANDARDS & SPECIFICATIONS FOR RAILWAY ELECTRIFICATION

RDSO/SPN/197/2008
Equipment’s with solid state components which are more susceptible to damage due to surges, transients and over voltages being encountered in the system due to lightning, sub-station switching such as Electronic Interlocking, Integrated Power supply equipment, Digital Axle counter, Data logger etc. shall Value of earth resistance shall not be more than

For conventional signaling equipment’s the earth resistance shall not be more than

10Ω

DHASHIN HARYANA BIJALI VITRAN NIGAM (DHBVN)

Specification no CSC-140 / DH/UH/P&D
Hose hold Earthing (3KA)

<8Ω

Commercial / Industrial Buildings (5KA)

<2Ω

Transformer / LT Line Earthing  (15KA)

1Ω to 2Ω

Transformer / Substation /HT Line ,HT Switchgear (40KA)

<1Ω

Lighting Arrester /Extra High Current appliances (50KA)

<1Ω

UPS / Data center / ATM

<0.5 Ω

*Earthing may be Single or Multiple Electrode.

Earthing Value

Earthing Condition Earthing Value
Best

0.1Ω to 2Ω

Good

2.1Ω to 5Ω

Need to be Maintenance

5.1Ω to 10Ω

Need to be Replacement

>10Ω

Difference between Fault Current and Short Circuit Current


Introduction:

  • There is a difference between “Fault Current” and “Short Circuit Current” in electrical system. Both parameters are important while selecting an Equipment or designing a Network, however both terms are misled in Electrical engineering.
  • In very simple language “Short” means less (shortest distance, time or circuit), Short circuit Fault means least resistance or no resistance in circuit and Current is high due to less resistance. This high current convert into heat energy. The opposite of a short circuit is an “open circuit”, which is an infinite resistance between two nodes.
  • While Fault means wrong. Fault Current means Current pass in to wrong path.

What is Fault Current

  • A fault current is a current which takes the wrong path instead of using the normal conducting path during Fault condition.
  • Under normal condition, the electric equipment operate at normal voltage and current ratings. Once the fault occurs in a circuit or device, voltage and current value deviates from their nominal Value. This may be high or Low Values.
  • The fault may be occurred due to insulation failures, Wrong Connection or conducting path failures, which further convert in Open Circuit, Short Circuit and Ground Fault.
  • A fault current can either current being more or less than the normal rated current.
  • In Three phase power system, there are basically three types of Fault Current.
  • Open Circuit Faults
  • Short Circuit Faults (L-L / L-L-L)
  • Ground Circuit Faults (L-G / L-L-L-G)

What is Short Circuit Current:

  • When a two or more conductors of differential potential comes to contact with each other (one phase comes in contact with other Phase, Neutral or Earth) gives the electricity to a path of less resistance hence a large current flow in the un-faulted phases, such current is called the short circuit current.
  • When Short circuit occurs, current returns to its source without passing to the load. It caused zero or very little resistance and No Voltage drop in that circuit.
  • This Current will be the maximum that the source can deliver for a very small time before the protection device operates. The current is limited only by the resistance of the rest of the circuit.
  • We know that V (Voltage) =I (current) x R (resistance of Circuit).
  • When short circuit occur, resistance is very small and can be considered as negligible. We can consider R=0. This means I = V/0, which means infinite current will Flow so the conductor must have the capacity to allow this huge current to flow. In most of the cases breakdown happens.
  • The resistance when short circuit occur is very small and can be considered as negligible. We can consider R=0.
  • This means V=Ix0, which means Voltage at Short circuit is very Less.
  • V(drop)=0 and current(I)=infinite
  • Short circuit gives thousands time larger Current than the normal current and Zero Voltage at Fault Point. This will produce more heat and result in burns and fires.
  • Short circuit faults are also called as Shunt faults.
  • Causes:
  • Over Loading of Equipment: Overloading of equipment and insulation failure due to lighting surges and mechanical damage.
  • Loose Connections:Due to Loose Connections, Sometimes Neutral and Phase wires to touch.
  • Faulty or Wrong Connections: Wrong Connections make Short circuit in Circuit.
  • Failure / Ageing of Insulation:Old or damaged insulation makes neutral and Phase wires to touch, which can cause a short circuit. Punctures in Insulation can damage insulation and makes short circuit.
  • Harmful Effects:
  • The short-circuit produces the arc that causes the major damage of equipment such as transformers and circuit breakers.
  • The short circuit causes a heavy current in the power system which produces excessive heat and hence results in fire or explosion.
  • The short circuit affects the stability of the network which disturbs the continuity of the supply.
  • The operating voltages of the system can go below or above their acceptance values that creates harmful effect to the service rendered by the power system.

Open Circuit Faults:

  • Open Circuit Faults occur due to the Failure / Open of one or more Phase Conductors in Circuit.
  • In Open Circuit Fault, Current cannot flow hence Current is Zero and Voltage become Infinite.
  • V(drop)=infinite and current(I)=0
  • Open circuit faults are also called as series faults. These are unsymmetrical or unbalanced type of faults except three phase open fault.
  • Causes:
  • Broken Conductor, Failure of Conductor Joints and malfunctioning of circuit breaker in one or more phases.
  • Harmful Effects:
  • Abnormal operation of the system.
  • Danger to the Human and Animals.
  • Exceeding the voltages beyond normal values in certain parts of the network, which leads to insulation failures and developing of short circuit faults.

Difference between Fault Current and Short Circuit Current:

Circuit Resistance:

  • A short circuit has zero resistance between two Wires / Circuits / Systems, on the other hand a Fault current has a resistance that draws current. The amount of resistance decides how much current is drawn and is usually caused by a breakdown in the insulation of a system.

Amount of Current:

  • Fault Current: it is the current exceeding the equipment current rating e.g. motor rated 25A, then more than this will be the fault current.
  • Short Circuit current: it is the maximum current which can flow when the equipment is short circuited & it can withstand. above this the current will damage the equipment.
  • Fault current is the current that flows during an Open Circuit or Short Circuit Fault condition so each time it is not necessary that Fault Current is a Short Circuit Current (It may be Open Circuit Fault).
  • A short-circuit current will flow when there is short-circuit in the system, and it will represent the highest possible fault current that a system can experience.
  • Therefore, a fault current can be less that the short-circuit current, and a short-circuit current will represent the highest fault current in the system.
  • A fault current can either current being more or less than the normal current while Short Circuit Current is higher than Normal Current.

  • A Fault Current is not necessary a short circuit Current but Short Circuit Current is always a Fault Current.

Comparison of Fault Current -Short Circuit Current

Basis For Comparison Fault Current (Open Circuit Fault) Short Circuit Fault Overload
Meaning In the Open circuit the voltage at the fault point is high up to infinite and current is zero through the faulty point of the network. In the short circuit the voltage at the fault point decreases to zero and current of irregular high value flow through the faulty point of the network. The overload means that load greater than the desired value have been imposed on the system.
Resistance High Zero
Current Zero High Low as compared to short circuit.
Voltage High Zero The voltage becomes low, but cannot be zero.
Occur It occurs when the neutral and live wire Break or Open. It occurs when the neutral and live wire touch each other. It occurs when a large number of devices are joint in a single socket.

Importance of Fault Current and Short circuit Current for designing of System or Panel.

  • The safety of the system is decided by short-circuit current rating (SCCR) of the Equipment with the reference of the available fault current where the Equipment is installed. 
  • The short circuit current rating gives a baseline for the fault current that an equipment can withstand for a specific amount of time, or until it clears the circuit with opening of a circuit breaker.
  • The short circuit current rating of a panel is the amount of energy, usually expressed as a value in kilo-Amperes (kA), that the panel can handle without causing fire, a shock hazard, or explosive danger.
  • In equipment with higher short-circuit current ratings compared to Fault Current is not an issue.
  • The available fault current of panel can be decided by the size of the upstream transformer, size of the electrical conductors / Cables up to the Equipment.
  • If the System Fault Current at the Location is 20KA to 50KA and if we use Equipment having short circuit current of 5KA to 10KA may cause damages of equipment or network in fault condition.
  • If the System Fault Current at the Location is 5KA to 10KA and if we use Equipment having short circuit current of 65KA to 100KA will not create any issue but it will unnecessarily increase the price of equipment hence short circuit level of the equipment is not too much high with respect of fault current.
  • We have to ensure that the Short Circuit Current is equal or more than Fault Current available at the point of Equipment.

Method for Installation of Conceal & Surface Conduits (Part-2)


4.Filling Chasing Area:

  • All grooves, chases shall be properly filled and concreted and finished up to the wall surface before plastering of walls is taken up. The conduit boxes, accessories, joints, etc. shall be laid along with the conduits. The chases shall be sufficiently deep and properly filled with cement mortar.
  • Where conduits pass through expansion joints in the building, adequate expansion fittings or other approved services shall be used to take care of any relative movement. As far as possible, chasing of wall to embed the conduits to be avoided.
  • Chasing is filled by Cement mortar 1:5 ratio(1 portion of the cement+5 portion of sand) shall be used for patchwork in chased area and its surface is rough so main plaster will easily joint on chasing area.
  • Curing shall be carried out for a minimum of three days.
  • Make sure the conduits are not visible from outside their route which could lead to improper plastering.

5.Wire Mesh:

  • After chasing area is filled by mortar, Chicken (wire) mesh and GI nails shall be applied on chasing area to avoid hair crack in plaster.
  • Width of Chicken Mesh is slightly larger than chasing Area. After installation of Chicken mesh final Plaster should be done.
  • Make Sure that Nails for Wire Mesh should not damage the Buried PVC Conduit.

A

6.Surface Conducting:.                                                           

  • Take the approved Drawings of Electrical conduit Shop Drawing with section details, MEP coordination drawing with section details and Architectural Drawings.
  • Ensure that the civil people have finished block wall and Plastering with adequate curing and clearance is given to proceed for electrical works.
  • Check the required reference markings are available for FFL (finished floor levels).
  • All required materials shall be shifted and stored under safe custody near workplace on daily basis as per planned quantity.

1 ) Marking of Conduits:

  • Site Engineer will carry out a site survey where the PVC Conduit will be installed as per approved shop drawings.
  • Mark the exact position of the conduit route with the blue marker string and then install conduit saddles.
  • All runs must be installed as a complete system before any conductors are pulled into them. In other words, a run of conduit (to include conduit, fittings, and supports) must be complete before the conductors are installed.
  • A run of conduit should be as straight and direct as possible. When a number of conduit runs are to be installed parallel and next to each other, install them all at the same time.

2) Installation of Conduits:

(A) PVC Conduit and Accessories:

  • Conduits shall run vertically or horizontally only for surfaced run conduits.
  • Install the correct Type and size of the conduits as per approved Specification and drawing.
  • Conduit pipes shall be fixed by heavy gauge saddles, secured to suitable wood plugs or other approved plugs with screws in an approved manner at an interval of not more than 1 meter but on either side of the couplers or bends or similar fittings, saddles shall be fixed at a distance of 30cm from the center of such fittings.
  • The saddles should not be less than 19MM (width) of 24 gauge for conduits up to 25 mm dia and not less than 25mm (width) of 20 gauge for larger diameter conduits.
  • Where conduit pipes are to be laid along the trusses, steel joint etc. the same shall be secured by means of special clamps made of MS. Where as it is not possible to drill holes in the trusses members suitable clamps with bolts and nuts shall be used.

B

  • Where conduit pipes are to be laid above false ceiling, either conduit pipes shall be clamp to false ceiling frame work or suspended with suitable supports from the ceiling slab.
  • For conduit pipe run along with wall, the conduit pipe shall be clamped to wall above false ceiling in uniform pattern with special clamps if required to be approved by the Engineer-In-Charge at site.
  • Check to ensure no sharp edges within the conduit joints for surfaced conduit and to ensure proper bonding for all conduit joint for concealed PVC conduit by foreman / skill worker / sub-contractor.
  • All joints in PVC conduits, other than screwed joints, shall be cemented with a waterproof adhesive. This adhesive shall be as recommended by the conduit manufacturer.
  • All saddles, tubes and boxes must be in perfect alignment to avoid any appearance of warping when the installation is complete. Saddles should not be so tight as to prevent expansion of the conduit.
  • Power conduit and LV conduit need to be separate. Power, Lighting Circuit should be run in separate conduit than LV circuit (Data wire, Telephone wire, TV wire) conduit.
  • Conduits shall not be run closer than 15m to any steam or hot water pipes and shall be run underneath such pipes rather than over them.
  • Conduits should not also be run closer than 05m to any telephone, bell or other signaling circuit.
  • Particular care shall be taken to ensure that no grout or other foreign materials enters the conduit system through joints, or through surface openings.
  • All conduits shall be run as far as possible along the walls and ceiling and above false ceilings so as to be easily accessible for inspection if need be. While the Architects drawings indicate the distribution for light and power points
  • PVC conduits shall be ISI grade and it shall be rigid type.  Where conduits are laid in straight run, draw boxes shall be provided at intervals not exceeding 10 meters.  Between two consecutive draw boxes the right angle bends shall not exceed two in number.
  • Drawn-in boxes must be provided to give access to all conduit for the drawing-in or out of any cable after the installation is completed.
  • Terminations of PVC conduits into switch boxes, DBs, etc. shall be with adapters.  PVC conduits shall be fixed to accessories such as coupler, circular boxes, etc. with vinyl cement.

(B) GI / Steel Conduit and Accessories:

  • GI Conduiting layout complete with MEP coordination and Architectural Drawing complete with section details.
  • Check the route of GI Conduiting free from debris and no obstruction of any other activity.
  • Arrange scaffolding of sufficient height approved by HSE officer.
  • Mark the reference points on wall/ column as per civil architectural drawing.
  • Identify the circuit start point and end & mark GI Conduiting route as per approved drawings.
  • Prior to erection, all burrs and sharp edges shall be removed from the conduit together with any dirt, oil or paint which may be present.
  • Standard length of conduits shall be cut to the required length.
  • For GI Conduits threading shall be done using a threading tools and appropriate die-set. Thread will be kept to a minimum from coupling and boxes. Zink rich paint to be applied to the exposed thread part of GI conduit.
  • Where required conduits shall be bent to the required radius using manual bending machines.
  • Conduits are fixed to the building fabric by means of distance saddle with appropriate metal screws will be allowed.
  • Spacer bar are fixed in regular interval not exceeding 1000mm and the distance from either side of ay box or bend to the nearest spacer bar shall not be more than 150mm.
  • All terminal boxes area marked on the appropriate location (wall/ceiling) as per approved shop drawing and fixed with metal screws and plug. Suitable bushes are used where conduit enters the boxes to avoid any damage to the wires.
  • Wherever necessary ropes shall be pulled into conduit runs ending and kept at pull boxes for the future purpose. Ensure that sufficient number of pull boxes is installed.
  • Metallic conduit boxes shall be sued throughout metallic conduit raceway system.
  • GI flexible conduits shall be used to make connections from un-accessible location and end connections to terminal boxes.
  • All pull boxes, junction boxes fixed on the wall in the route of steel conduit shall be provided with GI cover after pulling the wires.
  • Steel conduiting shall be conforming to relevant IS specifications (IS 9537). All steel conduits shall be of heavy gauge, welded and threaded type.  Conduit accessories such as boxes, bends, inspection bends, boxes, elbows, reducers, etc. shall conform to relevant standards.  As far as possible, boxes shall have internally tapped spouts to receive the conduits.
  • Where conduits are installed in straight run, draw boxes shall be provided at intervals not exceeding 30 feet (9 meters). Between two consecutive draw boxes, the right angle bends shall not exceed two in number. Conduits shall be properly threaded and screwed in to the accessories.
  • The minimum size of conduits used shall be 20 mm. The minimum thickness of the conduits shall be 16 SWG.
  • Wherever steel conduits terminate into points control boxes, distribution boards, etc. conduits shall be rigidly connected to the boxes, boards, etc. with check nuts on either side of the entry to ensure electrical continuity and with PVC or Bakelite bushes. Turning joints in conduits wherever necessary shall be rigidly held in aligned position by check nut tightened on the running side.
  • After conduits, junction boxes, outlets, etc. are fixed in position, their outlets shall be properly plugged with PVC stop cover or with any other suitable material so that water, mortar, vermin or any other foreign material do not enter into the conduit system.
Maximum number of PVC insulated 650/1100 V Copper conductor cable conforming to IS: 694-1990
Conduit size 20mm 25mm 32mm 40mm 50mm
Wire Size (Sq.mm) S B S B S B S B S B
1.5 Sq.mm 7 5 12 10 20 14
2.5 Sq.mm 6 5 10 8 18 12
4 Sq.mm 4 3 7 6 12 10
5 Sq.mm 3 2 6 5 10 8
10 Sq.mm 2 4 3 6 5 8 6
16 Sq.mm 2 4 3 7 6
25 Sq.mm 3 2 5 4 8 6
The columns heads ‘S’ apply to runs of conduits which have distance not exceeding 4.25 m between draw in boxes and which do not deflect from the straight by an angle of more than 15 degrees.
 The columns heads ‘B’ apply to runs of conduit which deflect from the straight by an angle of more than 15 degrees.

Bending of Conduit:

  • It may be necessary to create bends in the field by heating and deforming rigid conduit.
  • For heating the rigid conduit, use a heat gun or some other flameless heat source. Do not use an open flame to heat the conduit. The rigid conduit must be heated to approximately 125˚C in order to bend without kinking.
  • Heat a length of conduit equal to approximately 10 times the rigid conduit nominal diameter.
  • Once the rigid conduit has been adequately heated, bend it to the required angle plus 3 extra degrees. The additional angle will accommodate the “spring back” which will occur during cooling.
  • After bending of the conduit is completed, immediately cool the bend using water or cold air.
Conduit Bending Radius
Size of Conduit Radius to Center of  Conduit
12  mm 100 mm
20 mm 112 mm
25 mm 144.8 mm
30 mm 183.9 mm
40mm 208 mm
50 mm 238 mm
63 mm 266 mm
75 mm 330 mm
88 mm 370 mm
100 mm 403 mm
127 mm 609 mm
152 mm 762 mm

REFERENCES:.

  • IS 3854 1966: Switches for domestic and similar purpose.
  • IS 1293 1967: Three pin plug and socket outlets.
  • IS 4614 1968: Switch Socket outlet (non-interlocking type)
  • IS 6538 1971: Three pin plugs made of resistant materials.
  • IS 9537-3 (1983): Rigid plain conduits of insulating materials.
  • IS 3419 (1989): Fittings rigid non-metallic  conduits

Method for Installation of Conceal & Surface Conduits (Part-1)


(A) Purpose: .

  • This method explains the sequence of activity for safely installation of PVC / GI Conduits and it’s accessories in the concrete slabs / columns, in block works and on Surface as per the standard Practice and Code.

(B) Storage & Material Handling:.

  • The storage area must be free from dust and Water leakages / seepages.
  • Manufacturer recommendation shall always be followed in loading/unloading and storing of Material.
  • Material and its accessories shall be unloaded handle with care in designated area of the Store (Do not directly drop to Ground) to avoid any damages.
  • Materials shall be stored in a dry place which is free from water or from weather effects and protection should be given to the material by means of covering the material with Tarpaulin sheet.
  • The Material will be stacked / unload in the site store on a proper stand on wooden loft on a flat surface at a sufficient height from Ground.
  • If Material are dispatch in packs or pallets, each pack or pallet shall be lifted individually with suitable lifting equipment.
  • The material shall be transported / Shifted in their original packing to Site location.
  • The Material should be visually inspected for damage, which may have occurred during transport.
  • If the Material is found defective it shall not be installed and the cable shall be returned to the supplier for replacement.

(C) Inspection of Materials:.

  • Check The Material according to its Type, Size, Make
  • Visual inspection:
  • Type and Make of Conduit and Accessories Material
  • Length , Width and thickness of PVC / GI / MS Conduit Material and Accessories
  • Physical Damages Inspection:
  • Damage on Material and it’s Accessories
  • In case of any damages observed during inspection, the concern report will be issued and Material shall be returned to the supplier for replacement.

(D) Concealed Conduit in Slab / Column:.

  1. Shifting Material to Working Area:

  • PVC Conduit and its accessories shall be carefully unloaded or shifted to the site by using Crane/Hydra or by sufficient manpower and moved to a defined installation location.
  • Remove the packing and ensure that the material is free from transportation damages
  • Check and ensure that approved drawings, the correct size and type of Conduit & its accessories are ready for installation.
  • Ensure that Conduit and its accessories received from site store for the installation are free of rusty parts and damages.
  1. Marking Electrical Point / Wall Conduit Drop on Slab:

  • Ensure that the civil activities are finished I,e Slab Shuttering Work and Steel Work and Site is ready for Electrical Work on Slab.
  • After completing the first layer of steel, start marking of Ceiling Points and Wall Drop Points on Slab as per approved Site Drawings.
  • Mark first the wall location for lower floor in slab as per latest Architecture layout so that it will be easy to locate the drops for switch, Wall Light Points and any other drops required for electrical system.
  • Mark the opening size in Slab or in Beam i.e window, door and shaft as per approved electrical drawing to avoid passing wall conduit drop on that area.
  • Mark the Electrical points on the slab, Wall Conduit Drop in Beam as per approved Electrical Shop Drawing.
  • Make sure that marking of Wall conduit drop is placed in center of wall, it is not out from wall or not move to any face of wall.
  • For initially use marker / Chalk for making location of electrical point on slab and wall drop after that apply oil paint on that location before conducting work so after de shuttering ,the JB or conduit drop is easily visible on slab or on beam.
  1. Installation of Junction Box and Conduit:

  • Chalk will be used to mark the PVC conduit route. Make sure that size of conduit is as per approved Electrical Shop Drawing.
  • Ceiling Conduits shall be laid on the prepared shuttering work of the ceiling slab before concrete is poured. The conduits, boxes, accessories, joints, etc. shall be laid along with the conduits.
  • Use Deep Junction Box for surface mounted lighting Fixtures and for Cable Pulling.
  • Use long radius bend or make as per site requirement by using PVC Conduit bending spring.
  • Joints between PVC conduit + fittings shall be made with suitable adhesive.
  • Try to avoid the overlapping of conduits and keep some distance between the conduits for low current and power/Lights.
  • To maintain at least 20mm spacing gap between PVC conduits running in parallel. To allow adequate / sufficient space between formwork and conduit so that embedded conduit is fully covered by concrete and will not result in any honeycomb or structural defects in the future.
  • Concealed conduits in slabs shall be brought out as vertical drops in beams, wherever such drops are required.  All vertical conduits in beams shall be left protecting from the bottom of the beam. All such ends of conduits protecting from bottom of beams shall be provided with couplings to receive extension.
  1. Fixing of Conduit & Accessories:

  • The conduits shall be adequately fixed to prevent excessive movement and damage during the pouring and setting of concrete and shall be protected from mechanical damage.
  • For Double layer of rebar, PVC conduits shall be secured to the bottom of Top layer rebar and for Single Layer rebar, PVC Conduit should be secure at top of rebar with binding Steel Wire.
  • After completing the work, tight the conduits with binding wire .PVC Conduit should be bound at intervals of not more than 1 meters by binding short lengths of steel wire, of not less than 2mm diameter twisted around the conduit and reinforcing steel. Additional Steel bonding Wire also provide near each PVC Conduit Coupler, PVC Bends and near Junction Box
  • Check there is no damage in PVC Conduit and it’s accessories before concrete is poured.
  • The open ends of Conduit should be protected during concreting by caps or plugs to prevent the ingress of building material.
  • All Junction Box, Fan Box should be protected during concreting by filling thermo coal Sheets to prevent the ingress of building material.
  • Ensure conduits are not concealed until works has been inspected and approved.
  • Before the concrete pouring the PVC conduit installation to be inspected and approved by consultant/client/contractor.
  • During concrete pouring, keep electricians for taking care of conduit to avoid any damage by others or dislocation of joints.

(E) Recess / Concealed Conducting in Wall.

  • Ensure that bricks / Block masonry work is complete and Site is given for electrical works.
  • Check the required reference markings are available for FFL (finished floor levels).
  • All required materials shall be shifted and stored under safe custody near workplace on daily basis as per planned quantity.
  • In the case of building under construction, conduit shall be buried in the wall before plastering and shall be finished neatly after erection of conduit.
  • In case of exposed brick/rubble masonry work, special care shall be taken to fix the conduit and accessories in position along with the building work.
  1. Marking of Switch Box and Light Points:

  • Mark the location of switch/socket and conduit route on proper height based on approved shop drawing.
  • No conduit smaller than 20mm in diameter or larger than 32mm diameter shall be used.
  • Mark the location of Switch Box, DB, and Junction Box for Light Point on the wall from FFL.
  1. Wall Chasing:

  • After marking of conduit and Switch Box location, Wall chasing shall be done using wall cutting machine.
  • Hammer and chisel will be used on the chased portion to get uniform depth of 50 mm or as per standard specifications.
  • All chases, grooves shall be neatly made to proper dimensions to accommodate the required number and size of conduits and staples. The outlet boxes, point control boxes, inspection and draw boxes shall be fixed as an when conduit is being laid. The recessing of conduits in walls shall be so arranged as to allow at least 12 mm plaster over the same. 
  • The chase in the wall shall be neatly made and of ample dimensions to permit the conduit to be fixed in the manner desired.
  • Wherever the length of conduit run is more than 10 meters, then circular junction box shall be provided to permit periodical inspection and of facilitate replacement of wires, if necessary. These shall be mounted flush with the wall.
  • In place where the conduit is crossing at different ceiling height, uniform bending shall be done. The bending of conduit shall be done using proper bending springs.
  • Conduits will be cleaned with a round file from inside and outside of the pipe after cutting.
  • Connect the conduit by using PVC solvent with an adaptor to the junction box. Apply PVC Solvent cement on the portion of conduit entering into coupler wherever applicable.
  • PVC Conduits shall be duly fixed by using a hook or Nail. Distance of GI hook / Nail shall be maintained at 500 mm at intervals.
  • Embedded back box, JB shall be protected by covering with brown tape filled with jute/gunny bag.
  1. Installation of the Box / Enclosure:

  • At Planning and Designing Level, always Select DB Wall block work thickness should be 200 mm instead of 100 mm for easy DB installation.
  • For Properly Installation of DB and Switch Box, locate plaster level points near DB or Switch Board.
  • The mounted height of the Switch Board is generally 1200mm (Bottom of Switch Box) in all rooms ,300 mm near Bed and for DB it is generally 1800mm (bottom of panel) or as per approved Drawings.
  • Ensure the box size and accordingly cut a bit larger size of box in marked place of block wall with sufficient depth.
  • Fix the GI Metal box of appropriate size and level with the help of spirit level.
  • Installed the Switch Box and DB with the use of cement mortar around the box. Make sure that it is flush with finished plaster level.

s

  • The bottom portion of box should match the marked level as per consultant approved height for switch/ socket and/or as per local applicable wiring regulation requirements.
  • Apply cement filler to fix the box properly and leave for setting, insert the required lengths of conduits on their paths and don’t connect with boxes until next day.
  • Next day, after setting of box connect the dropped conduits for switch/socket to the box.
  • The switch box shall be flush with the plaster. The height of the switch boxes shall be as indicated in the drawings. The switch boxes should be sufficient depth to give minimum 20 mm plaster cover to conduits embedded.
  • Distribution board interiors will not be installed in cabinets until all conduits connections to the cabinet have been completed.
  • Trim for flush mounted cabinets will be installed in plaster frame, flushed with furnished wall.

Quick Reference-Fire Fighting (Part-3)


 

Pipe Support Details

Nominal Pipes Diameter

Hanger rod diameter

Hanging Strip Size(thickxwidh)

Spacing between supports

25 mm

8 mm

20 x 1 mm

2 Meter

32 mm

8 mm

20 x 1 mm

2.5 Meter

40 mm

8 mm

20 x 1 mm

2.5 Meter

50 mm

10 mm

25 x 1.2 mm

2.5 Meter

65 mm

10 mm

25 x 1.2 mm

2.5 Meter

80 mm

10 mm

25 x 1.2 mm

2.5 Meter

100 mm*

12 mm

25 x 1.6 mm

2.5 Meter

125 mm*

12 mm

25 x 2 mm

3 Meter

150 mm*

12 mm

25 x 2 mm

3 Meter

* As per Site Requirement Fabrication Support may be used.

Sprinkler Qty

Pipe Size

Min.Sprinkler Qty

Max.Sprinkler Qty

25 mm

1

2

32 mm

3

4

40 mm

5

7

50 mm

8

15

65 mm

16

30

80 mm

31

60

100 mm*

61

100

150 mm*

More than 100

Supporting Chanel & U Bolt

Pipe Size

Chanel

U Bolt Dia

Up to 50 mm

38x38xx6 mm

9 mm

65 To 100 mm

75x75x6 mm

12 mm

125 To 200 mm

88x88x9 mm

15 mm

 

Flange  Details

Pipe Dia

Flange Thickness

No. of holes

200 mm.

24 mm.

12

150 mm and 125 mm

22 mm.

8

100 mm and 80 mm

20 mm.

8

65 mm.

18mm

4

40 mm and below.

16mm

4

Pipe Support Details

MS Angle(mm)

Anchor Faster

Width

40X40X5

12MM

200MM both Side of Pipe

Holiday Test Voltage (IS 15337)

Thickness of Coating

Test Voltage, Max

2 mm

10KV

3 mm

12KV

4 mm

15KV

Recommended Welding Electrode Size

Average Thickness of Plate or Sections

Maximum Electrode Size

Current Range

1.5 To 2.0 mm

2.5 mm

60 To 95 Amp

2.0 To 5.0 mm

3.2 mm

110 To 130 Amp

5.0 To 8.0 mm

4.0 mm

140 To 165 Amp

>8.0 mm

5.0 mm

170 To 260 Amp

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