Main Breaker Rating

[booter]

I work for an electric utility. We are using meter sockets that are UL listed at 320 amps continuous and 400 amps maximum. I have had conversations with a licensed electrician concerning amp ratings of a main breaker. It is now my understanding that a 400 amp breaker rating means that 400 amps is a "maximum" rating and that the continuous rating is 20% or 80 amps less which puts it at 320.
The way we currently handle services with main service breakers of 400 amps for example is not to use the 320 amp socket but meter it with current transformers.
What I am trying to determine is whether I can issue the electrician a 320 amp UL listed socket when he is installing a 400 amp main and not violate any NEC requirements.

 

[bob]

Re: Main Breaker Rating

The continuous load should not exceed 80% of the breaker rating. Continuous load is load that is expected to last for more than 3 hours.

 

[travis]

Re: Main Breaker Rating

The 320amp base should be fine. the normal load should never exceed 320 amps or 80%

 

[bwyllie]

Re: Main Breaker Rating

Everything could be designed not to exceed the 320A, but what if in reality or in the future it does. The main circuit breaker won't trip until 400A, which will exceed the 320A rating of the meter socket.

 

[booter]

Re: Main Breaker Rating

bwyllie,
Is the 400 amp breaker a rated at 400 amp continuous amps or 400 maximum amps?

 

[hurk27]

Re: Main Breaker Rating

The 320 socket is UL listed for use with a 400 amp main and has been for a long time
This has been a standered install around here for as long as I can remember.

 

[frenchelectrican]

Re: Main Breaker Rating

i will make it more clear here for plug in meter socket is rated 320 amp max contuions but if more than that for contunious we go with bolt in socket it go much as 600 amp (400 amps before but went to 600 with electronic meter) and been a very long pratice for 320 class socket for too many years for redisental appaction but for commercal appication we go with bolt on meter for more durbity

merci marc

 

[caj1962]

Re: Main Breaker Rating

In our area the only time we can use the 320 amp socket is if we use 2-200 amp disconects. The utilties theory is if there is a problem it would likely be only on one of the disconrcts/panels

 

[charlie]

Re: Main Breaker Rating

We have been using the 320 ampere meter fitting for residential 400 ampere service for a long time. Additionally, we started using it for commercial 400 ampere services since we started using electronic metering.

We provide them at no cost to contractors and owners and have not had any problems to date. It is seldom that the demand is more than 1/2 the service size where the calculations are done in accordance with Article 220. Also, assume the calculations come to 250 amperes, most of the time a 400 ampere service will be installed.

I don't think that you have anything to be afraid of from an electric utility standpoint. This issue is out of the purview of the NEC. 90.2(B)(5)(a) states as not covered, "Installations under the exclusive control of an electric utility where such installations . . . Consist of service drops or service laterals, and associated metering."

 

[bonding jumper]

Re: Main Breaker Rating

I don't think is up to u, I believe the electric utility company will instruct you or has a book of guidelines that u must follow. I work with Con-Edison and they require a ct cabinet and 10 point meter on any service over 200A.

[ August 01, 2003, 05:55 PM: Message edited by: bonding jumper ]