when doing a single family load calc (standard method) i was taught a/c was calculated at 100%. I am in my fourth year of my apprenticeship and we are adding an additional 25% to the a/c load or the largest motor used in the calculation. where, if at all is this in the code and is it necessary? i have taken Mike's 7 hour exam and have his exam prep which have allowed me to pass my journeyman test as well as my masters and this is the first i have heard of this for this situation, any input would be appreciated!
standard method load calcs
- Thread starter justin
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Re: standard method load calcs
Justin
I agree with you about not requiring the added 25% for services. I think the confusion is in 220.3.B.3 which refers to motor outlets and refers to the the motor section. 430.22 and 430.24 plus 440.6 requires the 25%.
However 220.3 is for branch circuits and does not refer to services. There is a software program at this site under "Free Stuff" that caculates residential services and it added the 25%. I pointed it out to Mike and he told me that he had been doing it wrong for 25 yrs and had the program changed. He said that he had attended the electrical inspectors meetings and they agreed that it should not be added.
Justin
I agree with you about not requiring the added 25% for services. I think the confusion is in 220.3.B.3 which refers to motor outlets and refers to the the motor section. 430.22 and 430.24 plus 440.6 requires the 25%.
However 220.3 is for branch circuits and does not refer to services. There is a software program at this site under "Free Stuff" that caculates residential services and it added the 25%. I pointed it out to Mike and he told me that he had been doing it wrong for 25 yrs and had the program changed. He said that he had attended the electrical inspectors meetings and they agreed that it should not be added.
fredcallison
Member
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- Sacramento
Re: standard method load calcs
Suggest looking at 2002 NEC 220.14. This is under section H: Feeders and Services. This section refers to 430.24 which requires the load calculations to include 125% of the full-load current rating of the highest rated motor...
Suggest looking at 2002 NEC 220.14. This is under section H: Feeders and Services. This section refers to 430.24 which requires the load calculations to include 125% of the full-load current rating of the highest rated motor...
Re: standard method load calcs
Mac
I've looked at that example also. It does seem to conflict with my statement. However if you read the articles listed I did not find where they required the 25% adder for service conductors. Its added to feeders and branch circuits.
In fact that example was the reason that I sent an email to Mike Holt and questioned the adder.
As I said, it was being used in the residential sofware on this site to caculate service requirement. I felt that the program was incorrect and asked him to check. He responded back to me about his meeting with the inspectors.
[ September 23, 2003, 04:01 PM: Message edited by: bob ]
Mac
I've looked at that example also. It does seem to conflict with my statement. However if you read the articles listed I did not find where they required the 25% adder for service conductors. Its added to feeders and branch circuits.
In fact that example was the reason that I sent an email to Mike Holt and questioned the adder.
As I said, it was being used in the residential sofware on this site to caculate service requirement. I felt that the program was incorrect and asked him to check. He responded back to me about his meeting with the inspectors.
[ September 23, 2003, 04:01 PM: Message edited by: bob ]
sc57ford
Member
- Location
- South Carolina
Re: standard method load calcs
Art. 230.42(A) states the ampacity of the service entrance conductors, before the application of adjustment or correction factors, shall not be less than the sum of the noncontinuous loads PLUS 125 percent of the continuous loads.
Par. (2) allows for a slightly different calculation, the summation of the continuous and the noncontinuous loads if they terminate in a listed 100 percent rated breaker or OC device.
Art. 230.42(A) states the ampacity of the service entrance conductors, before the application of adjustment or correction factors, shall not be less than the sum of the noncontinuous loads PLUS 125 percent of the continuous loads.
Par. (2) allows for a slightly different calculation, the summation of the continuous and the noncontinuous loads if they terminate in a listed 100 percent rated breaker or OC device.
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