I am an instructor for the IBEW. Myself, and my fellow colleagues have been discussing this issue for quite some time. here's the question 230.42(B)states that "the minimum ampacity of ungrounded conductors for specific installations shall not be less than the rating of the service disconnecting means". Does that throw out the window the option provided by 240.4(B)that basically one could use a 500Kcmil copper conductor rated 75 degrees C with an ampacity of 380A, and protect them with a 400A breaker. A couple of us say you must use 600Kcmil for service entrance, and the others here believe 500Kcmil is adequate. Any help or opinions?
Service Entrance Condutor Ampacity
- Thread starter smenser
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bphgravity
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Re: Service Entrance Condutor Ampacity
For example, if I determine a total load of 55-amps for a single dwelling per 230.42(A), Part (B) tells me that I must go to 230.79(C) and per that section I must use 100-amp conductors and a 100-amp disconnect. If my calculated load is determined to be higher than 100-amp, I have met the conditions of 230.42(B).
[ May 02, 2003, 03:34 PM: Message edited by: bphgravity ]
The sentence continues to state "specified in 230.79(A) through (D)." When you go to these sections, it specifies the minimum sized disconnect ratings for each of the conditions (A) through (D). This does not mean ALL disconnects, just that these are the minimums. 500kcmil conductors would be compliant in my opinion.
For example, if I determine a total load of 55-amps for a single dwelling per 230.42(A), Part (B) tells me that I must go to 230.79(C) and per that section I must use 100-amp conductors and a 100-amp disconnect. If my calculated load is determined to be higher than 100-amp, I have met the conditions of 230.42(B). [ May 02, 2003, 03:34 PM: Message edited by: bphgravity ]
Re: Service Entrance Condutor Ampacity
Let me rephrase my previous question. I understand the requirements of 230.79(A) through (D),but lets say it is for a 400A service (non-residential)which would fall under the requirements for 230.79 Rating of Service Disconnecting Means, and 230.79(D) All Others. Now even if my calculated cont. and non cont. loads totaled lets say 375A. Can I use 500Kcmil for the 400A service.
Let me rephrase my previous question. I understand the requirements of 230.79(A) through (D),but lets say it is for a 400A service (non-residential)which would fall under the requirements for 230.79 Rating of Service Disconnecting Means, and 230.79(D) All Others. Now even if my calculated cont. and non cont. loads totaled lets say 375A. Can I use 500Kcmil for the 400A service.
bphgravity
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Re: Service Entrance Condutor Ampacity
Okay, I see what you are getting at. You are using a Circuit Breaker as your OCD and your disconnect. These can be two different things. As far as disconnects go, The rating can be higher than the rating of the conductors ampacity. Since you are using a CB as the service disconnect and the as the OCD, per 230.90(A), the OCD can not be larger than the rating of the conductors. So, for your description, I would say that you first determine the size of the service, which is 400-amp, and then you must size the conductors per that rating which indeed is 600kcmil.
Okay, I see what you are getting at. You are using a Circuit Breaker as your OCD and your disconnect. These can be two different things. As far as disconnects go, The rating can be higher than the rating of the conductors ampacity. Since you are using a CB as the service disconnect and the as the OCD, per 230.90(A), the OCD can not be larger than the rating of the conductors. So, for your description, I would say that you first determine the size of the service, which is 400-amp, and then you must size the conductors per that rating which indeed is 600kcmil.
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- retired electrician
Re: Service Entrance Condutor Ampacity
Exception #2 to 230.90(A) permits you to use 240.4(B) and round the OCPD up to the next standard size above the conductor ampacity.
Don
Exception #2 to 230.90(A) permits you to use 240.4(B) and round the OCPD up to the next standard size above the conductor ampacity.
Don
Re: Service Entrance Condutor Ampacity
I agree with Don. In the 1999 exception #2 of 230-90 allows you to use 240-3(b) for sizing your OCPD. As long as that device is less than 800A you can go higher than your load.
All services 800A and less
1. Determine load (cont and non-cont.)
2. Size conductors
3. Size OCPD
If it's over 800A, then the conductors must be greater than or equal to your OCPD.
So if your cont. plus non-cont. load was 380A @ 208V, 500Kcm on a 400A breaker would be fine, unless you have to count your nuetral as a CCC (current carrying conductor) per 310-15(3)(c) or your MCB is not listed for 100%. Although they did re-word 384-16(d)(1999) in 2002 NEC.
I agree with Don. In the 1999 exception #2 of 230-90 allows you to use 240-3(b) for sizing your OCPD. As long as that device is less than 800A you can go higher than your load.
All services 800A and less
1. Determine load (cont and non-cont.)
2. Size conductors
3. Size OCPD
If it's over 800A, then the conductors must be greater than or equal to your OCPD.
So if your cont. plus non-cont. load was 380A @ 208V, 500Kcm on a 400A breaker would be fine, unless you have to count your nuetral as a CCC (current carrying conductor) per 310-15(3)(c) or your MCB is not listed for 100%. Although they did re-word 384-16(d)(1999) in 2002 NEC.
Re: Service Entrance Condutor Ampacity
Thanks Guys, I appreciate all the good input. Not satisfied still,because like other areas there seems to be some contridctory statements between 230.90(A) exc#2 , and 230.42(B), and 240.4(B). Sounds like it's time for a proposed change.
Thanks Guys, I appreciate all the good input. Not satisfied still,because like other areas there seems to be some contridctory statements between 230.90(A) exc#2 , and 230.42(B), and 240.4(B). Sounds like it's time for a proposed change.
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- Illinois
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- retired electrician
Re: Service Entrance Condutor Ampacity
I don't see any real conflict here. 230.42(B) only applies to the small services listed in 230.79(A)-(D). In these limited cases, I would agree that you can't round up, but assuming the use of 60?C conductors the only one that would require a larger conductor is the 60 amp service. You would need #4 if you can't apply 240.4(B).
Don
I don't see any real conflict here. 230.42(B) only applies to the small services listed in 230.79(A)-(D). In these limited cases, I would agree that you can't round up, but assuming the use of 60?C conductors the only one that would require a larger conductor is the 60 amp service. You would need #4 if you can't apply 240.4(B).
Don
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- Illinois
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- retired electrician
Re: Service Entrance Condutor Ampacity
physis,
In this case "specific installations" are those installations listed in 430.79(A) through (D).
Don
physis,
In this case "specific installations" are those installations listed in 430.79(A) through (D).
Don
- Location
- Illinois
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- retired electrician
Re: Service Entrance Condutor Ampacity
physis,
Yes, my code reference should have been 230.79 not 430.79. Thanks.
physis,
Yes, my code reference should have been 230.79 not 430.79. Thanks.
Re: Service Entrance Condutor Ampacity
So a 400 amp service is a specific installation, as in 230.79(D) and if the ampacity of the service entrance conductors are not less than required by either 230.42(A)(1) or (2), then 230.42(B) would require the minimum ampacity for the ungrounded conductors to be equal to or greater than the rating of the disconnect. Does anyone know where or why the wording "specific installation" were added to this article?
So a 400 amp service is a specific installation, as in 230.79(D) and if the ampacity of the service entrance conductors are not less than required by either 230.42(A)(1) or (2), then 230.42(B) would require the minimum ampacity for the ungrounded conductors to be equal to or greater than the rating of the disconnect. Does anyone know where or why the wording "specific installation" were added to this article?
- Location
- Illinois
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- retired electrician
Re: Service Entrance Condutor Ampacity
In my opinion, it is not a "specific installation" per 430.79(D) if the service disconenct has a rating greater than 60 amps.
Don
In my opinion, it is not a "specific installation" per 430.79(D) if the service disconenct has a rating greater than 60 amps.
Don
Re: Service Entrance Condutor Ampacity
Don,
Can a one circuit instalation be higher than 15 Amps, A 2 circuit installation higher than 30 Amps, A one family dwelling higher than 100 Amps? If you answered yes to one or more of the questions above, then I don't see how 230.79(D)cannot apply to a 400Amp service. It does fall under "all others". I am not trying to be argumentative on this or beat this poor horse too much, just trying to get clarification of an ambiguous article.
[ May 07, 2003, 04:41 PM: Message edited by: smenser ]
Don,
Can a one circuit instalation be higher than 15 Amps, A 2 circuit installation higher than 30 Amps, A one family dwelling higher than 100 Amps? If you answered yes to one or more of the questions above, then I don't see how 230.79(D)cannot apply to a 400Amp service. It does fall under "all others". I am not trying to be argumentative on this or beat this poor horse too much, just trying to get clarification of an ambiguous article.
[ May 07, 2003, 04:41 PM: Message edited by: smenser ]
- Location
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- retired electrician
Re: Service Entrance Condutor Ampacity
smenser,
In my opinion the intent of 230.42(B) is that the wire ampacity shall not be less than that required by the minimum size service disconnect permitted in 230.79.
This was very clear in the '99 code.
Don
[ May 07, 2003, 06:56 PM: Message edited by: don_resqcapt19 ]
smenser,
In my opinion the intent of 230.42(B) is that the wire ampacity shall not be less than that required by the minimum size service disconnect permitted in 230.79.
This was very clear in the '99 code.
The change in '02 was intened to clarify the section, not change its meaning, but the old wording was better.
Don
[ May 07, 2003, 06:56 PM: Message edited by: don_resqcapt19 ]
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