sizing of service conductors

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buck33k

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Washington state and North Carolina
I'd like to get a better understanding of 230.90 as compared to 230.31(A) and 230.42(A).

Can service laterals and service entrance conductors have a lower ampacity than the rating of a service overcurrent device providing the conductors are sized to the calculated load?

Buck
 
Re: sizing of service conductors

Doesn't 230.42(B) answer the question?

Edit: There is a lot of bouncing around involved.

Edit again: And why it's called Specific Installations. I have no idea. I'm sure there's a reason but I don't know what it is.

[ May 16, 2005, 01:56 PM: Message edited by: physis ]
 
Re: sizing of service conductors

Yes. the size of the service conductors is determined by the calculated load, conductors are installed to meet the calculated load. You can round up to the next standard size OCPD. For example a 501 amp load can have a 600 ampere OCPD

[ May 16, 2005, 01:58 PM: Message edited by: tom baker ]
 
Re: sizing of service conductors

It's probably easier to understand if you start from article 220.

I'm looking at 220 right now. And I don't see where it says that 220 is where you can determine service conductor ampacity.

Maybe it should be mentioned in 220.1 or 220.10.
 
Re: sizing of service conductors

Thankyou Tom. I think the wording of 230.90(A) is what I wonder about. It says the service equiptment overcurrent device must have a rating not higher than the service conductor. I know you are right, but what about 230.90(A)?
 
Re: sizing of service conductors

I guess I wasn't seeing your question too clearly.

I first thought you were asking about determining service conductor ampacity.

I think I get it now, it's about 230.90.

It doesn't make a ton of sense to me either.
 
Re: sizing of service conductors

Sam
Just something simple I'm not understanding. As Tom pointed out, service lateral and service entrance conductors are sized to Art 220. Its relating 230.90(A) that gives me trouble. It says the rating of the service overcurrent device can not be higher than the ampacity of the service conductors. I think what Tom is saying is that they can be smaller if they don't conform to standard size overcurrent protection, (and they are 800 amps or less), but I'm not sure.
Buck
 
Re: sizing of service conductors

Buck33k,

230.31 tells you that the service conductors must be large enough for the load.

230.90 tells you OCP is required and (normally) the rating or setting of the OCPD not be higher than the allowable ampacity of the conductor.

230.90(A) exceptions The 5 exceptions tell you where the OCPD can be set higher for the reasons stated in the exception


if this don't help,post agian.

frank
 
Re: sizing of service conductors

This is all relevant if an EC does the job the poco has thier own agenda they go by ;)
 
Re: sizing of service conductors

Thanks for all the responces. I guess I was making it too difficult.
The service conductors must be sized for the load and a SINGLE service overcurrent device must have a rating not higher than the ampacity of the service conductors.
Buck

edited to say the service overcurrent device must have a rating not higher than the service conductors.

[ May 16, 2005, 10:04 PM: Message edited by: buck33k ]
 
Re: sizing of service conductors

230.90 Exception #2 references 240.4(B) and 240.4(C) and 240.6. This is an example of how NEC reads like stereo directions.
 
Re: sizing of service conductors

230.09 Exception #3 is a can of worms and can create a hazard similar to spit ( deliberately misspelled ) bus panelboards. You can theoretically have 1600 amps circuit breakers in a 1200 amp power panel with only 1200 amp supply conductors.

The primary problem with circuit breaker spit bus panelboards was that they were not required to have service conductors the same rating as the line bus and it was possible to put in a bunch of 60 amp or 100 amp circuit breakers. The one that used say 4 pullout blocks were not so bad because they could be designed to accept no more than 180 amps, 220 amps, 250 amps or whatever of fuses. The service conductors could then be sized for the maximum complement of fuses.
 
Re: sizing of service conductors

Here is an example of service conductors that have a lower ampacity than the total overcurrent protection. [230.90(A)Exception No. 3]

Around here this is a fairly typical low cost muiltdwelling unit service.

:)
 
Re: sizing of service conductors

Originally posted by tom baker:
Yes. the size of the service conductors is determined by the calculated load, conductors are installed to meet the calculated load. You can round up to the next standard size OCPD. For example a 501 amp load can have a 600 ampere OCPD
Click to expand...
But that's only if it's under 800 amps, right?

Lady :)
 
Re: sizing of service conductors

Thankyou for posting the photo Bob.
I was looking at the 6th meter on the right. It almost looks like duct seal around the nipple. What would be required here? A Meyers hub, sealing locknut? Do we have a choice?

A photo forum might be a good idea.

But that's only if it's under 800 amps, right?
Click to expand...
Hi Lady. Yes, I would say 240.4(B) was in mind.

Buck
 
Re: sizing of service conductors

Wait a cotton pickin' minute.

How do you get away with having six meters feeding six different MDP's in various locations to comply with 230.72(A)? Do you call all six units separate structures? :confused:
 
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