Calculating Service Size

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KWH

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When you are calculating your service size do you always figure your main breaker @ 80% or is it common for main's to be rated @ 100% by the manufactuer.
 
If a calculated load is 99 amps you can install a 100 amp service. What do you mean by 80% and 100%? Are you asking about the amount of load you would allow, 80% or 100%?
 
More Info on the Service

More Info on the Service

What I am asking is lets say you have 70 lights with a ballast amp rating of 7amps @ 240volt single phase if you use the ballast amp rating only are you allowed to exceed 80% of the breaker versus ballast amp rating x 1.25 then you can go to 100% of the rating of the main. I am sizing a job for a ballfield and dealing with only light fixture's.
 
KWH said:
What I am asking is lets say you have 70 lights with a ballast amp rating of 7amps @ 240volt single phase if you use the ballast amp rating only are you allowed to exceed 80% of the breaker versus ballast amp rating x 1.25 then you can go to 100% of the rating of the main. I am sizing a job for a ballfield and dealing with only light fixture's.
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70x7x240x1.25= service size
 
KWH said:
What I am asking is lets say you have 70 lights with a ballast amp rating of 7amps @ 240volt single phase if you use the ballast amp rating only are you allowed to exceed 80% of the breaker versus ballast amp rating x 1.25 then you can go to 100% of the rating of the main. I am sizing a job for a ballfield and dealing with only light fixture's.



In that case 220.3 (b) (1)and then 220.22
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KWH said:
What I am asking is lets say you have 70 lights with a ballast amp rating of 7amps @ 240volt single phase if you use the ballast amp rating only are you allowed to exceed 80% of the breaker versus ballast amp rating x 1.25 then you can go to 100% of the rating of the main. I am sizing a job for a ballfield and dealing with only light fixture's.
Click to expand...

Forget the lamp size when calculating the load. You need to use the actual load which is provided by the information on the ballast. If you look at Jumper's calculation you'll see that the 125% factor is included in the calculation so you can use the calculated value at 100%.
 
mcclary's electrical said:
KWH said:
What I am asking is lets say you have 70 lights with a ballast amp rating of 7amps @ 240volt single phase if you use the ballast amp rating only are you allowed to exceed 80% of the breaker versus ballast amp rating x 1.25 then you can go to 100% of the rating of the main. I am sizing a job for a ballfield and dealing with only light fixture's.



In that case 220.3 (b) (1)and then 220.22
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Are those 08 references?
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iwire said:
IMO if your NEC load calculation finishes at 100.00 amps you may install a 100 amp service with a typical 100 amp breaker.
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I agree. The calculation has added in the needed 125% factor where applicable. Might not be the best design but code compliant.
 
To provide further clarity, correct me if I am wrong, per 230.42(A)(2) you would NOT need to inlcude the 1.25 factor if terminating in an overcurrent device listed with its assembly for 100% operation.

Otherwise, include the 1.25 factor because lighting is a continuous load
 
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