Panel sizing

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wesley1

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Port St. Joe, Florida
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Electrical contractor owner
I am looking for some help in sizing a panelboard that will be supplying 30 120 volt 2000 watt lights. The voltage is 120/208 3 phase. 60,000 watts/208x1.732= 167 amps. It has been so long since I have had to calculate this stuff, this has really woke me up to how much i have forgotten. The lights will all be operating at the same time but probably not for 3 hrs so do I add the 125% for continious load. Also as bad as it sounds i am not sure if the above 167 amp demand was figured correctly. I do know tonight the study books come back out. Thanks for any help!
 
I agree with Dennis, but it's not my money :smile:
If all is balanced, your numbers would be correct, 167 amps.
If you use "standard equipment" that will be a 200 amp panelboard. Unless $$ is a big issue, a 225 won't be that much more expensive.
 
wesley1 said:
I am looking for some help in sizing a panelboard that will be supplying 30 120 volt 2000 watt lights. The voltage is 120/208 3 phase. 60,000 watts/208x1.732= 167 amps. It has been so long since I have had to calculate this stuff, this has really woke me up to how much i have forgotten. The lights will all be operating at the same time but probably not for 3 hrs so do I add the 125% for continious load. Also as bad as it sounds i am not sure if the above 167 amp demand was figured correctly. I do know tonight the study books come back out. Thanks for any help!
Click to expand...

Well take the 30 circuits divide by 3 = 10 circuits on each leg then take 20,000 watts = 166.6666 amps per leg = 167 amps and yes add continuous load i would to be safe what type of lighting ?
 
Before we go deciding to call it a continuous load which could very well be a costly unnecessary decision we should really consider the definition of continuous load is.

All 30 lights would have to be expected to be used for three hours or more. It does not say where it might run three hours or more.

Now that said .........

30*2000= 60,000

60,000/208/1.732*1.25= 208.18529 amp

No problem a commonly available 225 amp panel will work fine and 75 KVA trans nails it exactly.

75,000/208/1.732= 208.18529 amp
 
wesley1 said:
I am looking for some help in sizing a panelboard that will be supplying 30 120 volt 2000 watt lights. The voltage is 120/208 3 phase. 60,000 watts/208x1.732= 167 amps. It has been so long since I have had to calculate this stuff, this has really woke me up to how much i have forgotten. The lights will all be operating at the same time but probably not for 3 hrs so do I add the 125% for continious load. Also as bad as it sounds i am not sure if the above 167 amp demand was figured correctly. I do know tonight the study books come back out. Thanks for any help!
Click to expand...

OP states 120 volt lights...
2000 watts / 120 volts = 16.667 amps
16.667 amps x 30 loads = 500 amps
500 amps (without considering continuous duty) = really big money

or am I just real tired and I missed something?
 
ray cyr said:
OP states 120 volt lights...
2000 watts / 120 volts = 16.667 amps
16.667 amps x 30 loads = 500 amps
500 amps (without considering continuous duty) = really big money

or am I just real tired and I missed something?
Click to expand...

if you are questioning the amps...he stated 3~ 208/120 so 500/3= 166 amps per phase
 
what type of lights are they ? (are they flourescent ? is the input 2000 watts ? - if not the calculation is wrong - 220.14 D & 220.18 B) also, what type of occupancy ? (you can use table 220.42 to apply a demand factor to the lighting load for certain occupancies) (for the feeder, not sure if that's part of what you're sizing)
 
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wesley1 said:
I am looking for some help in sizing a panelboard that will be supplying 30 120 volt 2000 watt lights. The voltage is 120/208 3 phase. 60,000 watts/208x1.732= 167 amps. It has been so long since I have had to calculate this stuff, this has really woke me up to how much i have forgotten. The lights will all be operating at the same time but probably not for 3 hrs so do I add the 125% for continious load. Also as bad as it sounds i am not sure if the above 167 amp demand was figured correctly. I do know tonight the study books come back out. Thanks for any help!
Click to expand...

What type of lamps?

The wattage sounds 'nominal' and if ballasts are used they usually take more W's. Best to use the Ampere rating of the ballast for your calculations. If ballasts are used, investigate if it will represent a non-linear load and select your transformer accordingly.

Are you leaving room for expansion?

How will this be switched?
 
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