Panel Design / Calculate Size of Bus bar


ScreenHunter_01 Jul. 21 20.06

  • Calculate Bus Bar Cross Section Area
  • Calculate Current Rating of Bus Bar
  • Calculate Peak elector-magnetic Force between Phase Conductors
  • Calculate Force on Insulator of Bus bar Support.
  • Calculate Mechanical Strength of Bus Bar.
  • Calculate Maximum Temperature Rise of Bus Bar.

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Calculate Voltage Drop and No’s of Street Light Pole

ScreenHunter_01 Jul. 14 20.14

  • Calculate Voltage drop in Street Light Pole
  • Calculate Distance between Each Street Light Pole
  • Calculate Wattage of each Street Light Luminaire
  • Calculate Required Street Light Watt as per Given Area.
  • Calculate Luminaire Payback Period

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Calculate Size of Neutral Earthing Transformer (NET)

  • Calculate Total Capacitive charging current (It).
  • Calculate Neutral Earthing Transformer  Secondary Current.
  • Calculate Required Grounding Resistor value at primary side (Rp).
  • Calculate Required Resistance value at secondary side (Rsec).
  • Calculate Neutral Earthing Transformer X/R Ratio
  • Calculate Fault current through Neutral (single line to ground fault) (If)
  • Calculate Rating of Neutral Earthing Transformer (P).

ScreenHunter_01 Jun. 06 22.20

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Calculate Street Light Pole’s Distance / Fixture Watt / Lighting Area

(1) Calculate Distance between each Street Light Pole:

Example: Calculate Distance between each streetlight pole having following Details,

  • Road Details: The width of road (w) is 11.5 Foot.
  • Pole Details: The height of Pole is 26.5 Foot.
  • Luminaire of each Pole: Wattage of Luminaries is 250 Watt, Lamp Out Put (LL) is 33200 Lumen, Required Lux Level (Eh) is 5 Lux, Coefficient of Utilization Factor (Cu) is 0.18, Lamp Lumen Depreciation Factor (LLD) is 0.8, Lamp Lumen Depreciation Factor (LLD) is 0.9.
  • Space Height Ratio should be less than 3.


  • Spacing between each Pole=(LL*CU*LLD*LDD) / Eh*W
  • Spacing between each Pole=(33200×0.18×0.8×0.9) / (5×11.5)
  • Spacing between each Pole= 75 Foot.
  • Space Height Ratio = Distance between Pole / Road width
  • Space Height Ratio = 3. Which is less than define value.
  • Spacing between each Pole is 75 Foot.

(2) Calculate Street Light Luminaire Watt:

Example: Calculate Streetlight Watt of each Luminaire of Street Light Pole having following Details,

  • Road Details: The width of road (w) is 7 Meter. Distance between each Pole (D) is 50 Meter.
  • Required Illumination Level for Street Light (L) is 6.46 Lux per Square Meter. Luminous efficacy is 24 Lumen/Watt.
  • Maintenance Factor (mf) 0.29, Coefficient of Utilization Factor (Cu) is 0.9.


  • Average Lumen of Lamp (Al) = 8663 Lumen.
  • Average Lumen of Lamp (Al) =(LxWxD) / (mfxcu)
  • Average Lumen of Lamp (Al)= (6.46x7x50) / (0.29×0.9)
  • Average Lumen of Lamp (Al)=8663 Lumen.
  • Watt of Each Street Light Luminar = Average Lumen of Lamp / Luminous efficacy
  • Watt of Each Street Light Laminar = 8663 / 24
  • Watt of Each Street Light Luminaire = 361 Watt

(3) Calculate Required Power for Street Light Area:

Example: Calculate Streetlight Watt of following Street Light Area,

  • Required Illumination Level for Street Light (L) is 6 Lux per Square Meter.
  • Luminous efficacy (En) is 20 Lumen per Watt.
  • Required Street Light Area to be illuminated (A) is 1 Square Meter.


  • Required Streetlight Watt = (Lux per Sq.Meter X Surface Area of Street Light) / Lumen per Watt.
  • Required Streetlight Watt = (6 X 1) / 20.
  • Required Streetlight Watt = 0.3 watt per Square Meter.

IP Rating for Electrical Enclosure

IP rating:

  •  IP letters stand for “International Protection” rating or “Ingress Protection” rating. IP ratings are defined in international standard (British BS EN 60529, IEC 60509).
  • It is used to explain levels of sealing effectiveness of electrical enclosures against foreign bodies (tools, dirt etc) and moisture.


Meaning of IP Rating:

  • The IP rating code is a two-digit (or optionally three-digit) designator to standardize the rating of protection level against intrusion of solids and liquids into mechanical and electrical enclosures. An enclosure can be a piece of equipment, an assembly unit, a cable or simply a connector.
  • The numbers of IP of each have a specific meaning.
  • First Number: The first Number indicates the degree of protection from moving parts, as well as the protection of enclosed equipment from foreign bodies.
  • Second Number: The second Number indicates the protection level that the enclosure enjoys from various forms of moisture (drips, sprays, submersion etc).
  • Third Number: The third digit in the designator is not part of the official IEC standard and is sometimes included (but more often omitted) to reference additional protections.

Abbreviation of IP Rating:


                                                                IP Rating Digits

IP Rating First Digit Second Digit Third Digit (Optional)
Solid Objects Protection Liquids Protection Mechanical impacts


No special protection No protection. No protection.
1 Protected against solid objects greater than 50mm in diameter ( such as large part of the body like hand) Protection against vertically falling drops of water e.g. condensation. Protects against impact of 0.225 joule (150 g weight falling from 15 cm height)
2 Protected against solid objects over 12 mm in diameter (person’s fingers) Protection against direct sprays of water up to 15° from the vertical. Protected against impact of 0.375 joule (250 g weight falling from 15 cm height)
3 Protected against solid objects not greater than 80mm in length and 12mm in diameter (tools and wires). Protected against direct sprays of water up to 60° from the vertical. Protected against impact of 0.500 joule (250 g weight falling from 20 cm height)
4 Protected against solid objects larger than 1 mm diameter (tools, wires, and small wires). Protection against water sprayed from all directions (limited ingress permitted). Protected against impact of 2.0 joule (500 g weight falling from 40 cm height)
5 Protected against dust limited ingress (no harmful deposit). Protected against low pressure jets of water from all directions (limited ingress). Protected against impact of 6.0 joule (1.5 kg weight falling from 40 cm height)
6 Totally dust tight. Protected against temporary flooding of water, e.g. for use on ship decks (limited ingress permitted). Protected against impact of 20.0 joule (5 kg weight falling from 40 cm height)
7 N/A Protected against the effect of immersion between 15 cm and 1 m. N/A
8 N/A Protects against long periods of immersion under pressure. N/A



  • IP65 Enclosure: IP rated as protection against dust (6) and protection from low water pressure (5). 
  • IP66 Enclosure – IP rated as protection against dust (6) and protected against heavy seas or powerful jets of water (6)



Calculate No of Street Light Poles

Typical Calculation of Road Lighting:

  •  Luminaries are properly selected and mounted on a location most feasible and effective with minimum cost. For a 230 volts system, a voltage drop of 5% is allowed although in extreme cases 15% voltage drop is sometimes tolerated.  3
  • Street illumination level in Lux (E)=(Al x (cu x mf)) / (w x d)
  • E = The illumination in Lux
  • w = Width of the roadway
  • d = Distance between luminaries
  • cu = Coefficient of utilization. Which is dependent on the type of fixture, mounting height, width of roadway and the length of mast arm of outreach?
  • Al = Average lumens, Al = (E x w x d) / Cu x mf
  • The typical value of Al is
  • 20500 lumens for 400 watts
  • 11500 lumens for 250 watts
  • 5400 lumens for 125 watts
  • The value of Al varies depending upon the type of lamp specified.
  • mf : It is the maintenance factor (Normally 0.8 to 0.9)

 (1) Calculate Lamp watt for street Light Pole:

  • Calculate Lamp Lumen for street Light Pole having Road width of 7 meter, distance between two Pole is 50 meter, Maintenance factor is 0.9, Coefficient of utilization factor is 0.29, light pedestrian traffic is medium and Vehicular traffic is very light and Road is concrete road.
    From Above table Recommended of illumination (E) in Lux is 6.46 per sq. meter.
    w = 7.00 meters , d = 50 meters , mf = 0.9, cu = 0.29
    To decide Lamp Watt It is necessary to calculate Average Lumens of Lamp (Al).
  • Average Lumen of Lamp (Al)=(E x w x d) / Cu x mf
  • Al=(6.46x7x50)/(0.29×0.9)= 8662.83 Average lumen
    Lamp lumen of a 250 watts lamp is 11,500 lm which is the nearest value to 8662.83 lumen. Therefore, a 250 watts lamp is acceptable.
    Let’s Computing for the actual illumination E for 250 Watt Lamp
  • Illumination (E)=(Al x (cu x mf)) / (w x d)
  • E= (11500×0.29×0.9) / (7×50) = 8.57 lumen per sq meter.
    Actual illumination (E) for 250 Watt is 8.57 lumen per sq meter which is higher than recommended illumination (E) 6.46.
  • Hence 250 watt gives adequately lighting.

 (2) Calculate Spacing between two Light Poles:

  • Calculate Space between Two Pole of Street Light having Fixture Watt is 250W , Lamp output of the Lamp (LL) is 33200 lumens , Required Lux Level (E) is 5 lux , Width of the road (W) = 11.48 feet (3.5 M),Height of the pole (H) = 26.24 feet (8 M) ,Coefficient of utilization (CU) = 0.18, Lamp Lumen Depreciation Factor (LLD) = 0.8 ,Luminaries dirt Depreciation Factor (LDD) = 0.9
  • Luminaries Spacing (S) = (LLxCUxLLDxLDD) / (ExW)
  • Luminaries Spacing (S) = (33200×0.18×0.9×0.8) / (5×11.48)
  • Luminaries Spacing (S) = 75 feet (23 Meters)

 (3) Calculation of the allowed illumination time:

  • The allowed illumination time in hours T = k.t.1000/E.
  • Where: k = extension factor
  • t = permissible time in hours at 1000 lux, unfiltered daylight
  • E = luminance (lx)


Extension Factor
Lamp Extension Factor
Incandescent lamps, 2.7 to 3.2
Halogen reflector lamps 2.5 to 3.5
Halogen capsules 2.5 to 3.5
High-pressure metal-halide 1.1 to 2.1
High-pressure sodium lamps 4
Fluorescent lamps 1.9 to 2.7


  • Example:
  • In sunlight (100000 lux) and extension factor 1: The permissible illumination time (T) =1 x 70 x 1000/100 000 = 0.7 hour.
  • In halogen light (200 lux) and extension factor 2.3: The permissible illumination time (T) = 2.3 x 70 x 1000/200 = 805 hours.
  • In UV-filtered halogen light (200 lux) and extension factor 3.5: The permissible illumination time (T) = 3.5 x 70 x 1000/200 = 1225 hours.

 (4) Calculate Uniformity Ratio:

  • Once luminaries spacing has been decided It is necessary to check the uniformity of light distribution and compare this value to the selected lighting
  • Uniformity Ratio ( UR) = Eav /Emin
  • Eav= average maintained horizontal luminance
  • Emin = maintained horizontal luminance at the point of minimum illumination on the pavement

 (5) Energy Saving Calculations:

  • At a simplistic level, the cost of running a light is directly related to the wattage of the globe plus any associated ballast or transformer. The higher the wattage, the higher the running cost and it is a straightforward calculation to work out the running cost of lamp over its lifetime:
  • Running cost = cost of electricity in $/kWh x wattage of lamp x lifetime in hours.

 Calculate Lux Level for Street Lighting

  • The Average Lux Level of Street Light is measured by 9 point method. Make two equal quadrants between two Street light poles. on the lane of light poles( one side pole to road).
  • We have 3 points P1,P2 and P3 under the light pole then P4 & P7 are points opposite pole 1 or Point P3 same is applicable for P6 and P9 for Pole 2.
  • The average lux = [(P1+P3+P7+P9)/16]+[(P2+P6+P8+P4)/8]+[P5/4]


Calculate No of Lighting Fixtures / Lumen for Indoor Lighting

  • An office area is 20meter (Length) x 10meter (width) x 3 Meter (height). The ceiling to desk height is 2 meters. The area is to be illuminated to a general level of 250 lux using twin lamp 32 watt CFL luminaires with a SHR of 1.25. Each lamp has an initial output (Efficiency) of 85 lumen per watt. The lamps Maintenance Factor (MF) is 0.63 ,Utilization Factor is 0.69 and space height ratio (SHR) is 1.25


 Calculate Total Wattage of Fixtures:

  • Total Wattage of Fixtures= No of Lamps X each Lamp’s Watt.
  • Total Wattage of Fixtures=2×32=64Watt.

 Calculate Lumen per Fixtures:

  •  Lumen per Fixtures = Lumen Efficiency(Lumen per Watt) x each Fixture’s Watt
  • Lumen per Fixtures= 85 x 64 = 5440Lumen

 Calculate No’s of Fixtures:

  •  Required No of Fixtures = Required Lux x Room Area / MFxUFx Lumen per Fixture
  • Required No of Fixtures =(250x20x10) / (0.63×0.69×5440)
  • Required No of Fixtures =21 No’s

 Calculate Minimum Spacing Between each Fixture:

  •  The ceiling to desk height is 2 meters and Space height Ratio is 1.25 so
  • Maximum spacing between Fixtures =2×1.25=2.25meter.

 Calculate No of Row Fixture’s Row Required along with width of Room:

  •  Number of Row required = width of Room / Max. Spacing= 10/2.25
  • Number of Row required=4.

 Calculate No of Fixture’s required in each Row:

  •  Number of Fixture Required in each Row = Total Fixtures / No of Row = 21/4
  • Number of Fixture Required in each Row = 5 No’s:

 Calculate Axial Spacing between each Fixture:

  •  Axial Spacing between Fixtures = Length of Room / Number of Fixture in each Row
  • Axial Spacing between Fixtures =20 / 5 = 4 Meter

 Calculate Transverse Spacing between each Fixture:

  •  Transverse Spacing between Fixtures = width of Room / Number of Fixture’s row
  • Transverse Spacing between Fixtures = 10 / 4 = 2.5 Meter.



  •  No of Row for Lighting Fixture’s= 4 No
  • No of Lighting Fixtures in each Row= 5 No
  • Axial Spacing between Fixtures= 4.0 Meter
  • Transverse Spacing between Fixtures= 2.5 Meter
  • Required No of Fixtures =21 No’s



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