ECN Forum Forums General Topics of the Trade General Discussion Area 400 amp service

The state I used to work it, it was common pratice for a 400amp residential service to really be a 320amp. The meter was a 320amp rated meter socket that feed 2 200amp (main breaker) panels with 2" pipes and 3/0's to each panel. I have changed to a different region, and am wondering if this is standared everywhere or if this is not the right way to do this.

It is fine, a 320 meter is rated 320 amps continuous, 400 amps non-continuous.

If a 400 amp service is properly sized it will not exceed 320 amps continuously.

Common practice in Mass. 320 amp continuous for a 400 amp service. 80%. I believe you have to be the full 400 amp on commercial services. Most of the electricians around here install it exactly how you explained except they use 4/0-3 SEU/AL. No pipe. Your way is much better, I guess around where I am they go the bare minimum requirements.

wirenutt.. what do you guys in Mass. run for 400amp UG services?? what would be a typical meter and panel configuration be. Thanks..ToHo

The only reason I can see that requirement is if you used 100% rated breakers and equipment.

A typical 400 amp breaker is only UL listed for 320 amps continuous or 400 amp non-continuous.

Bob

Thats how the 400 amp resedential are set up around here in IL. We don't call it a (2) 200 or 320 amp. Maybe more of a sales thing. Don't want to be pricing out a 320 amp when the other EC has the same set up calls it a 400 amp.

Tom

Tom,
Im in IL I think around your area. Suburbs of Chicago. So using a 320amp meter socket with 2/200amp panels is ok for the 400 amp service?

Yep.

At the supply we just ask for a 400 amp pedistal but they know we mean 320 amp. Milbanks catolog for Com Ed only shows single phase 320 not 400 amp meter housings. Com Ed resi feeds underground are normaly 200 and 320 a. Overhead 100, 200, and 320 a.

We would only bond one panel and would run a larger water pipe ground than a single 200 a service, I think 1ott. You could do it other ways.

Tom

TOHO; Mostly the Milbank # 2448-X meter socket. One EC uses 500 kcmil xhhw. Murray also makes a unique 400 amp double main break panel that's kind of interesting. Guess it depends on your situation.

Tom
What do you mean by, "bond only one panel"?

Pierre

Tom I was wondering the same thing as Pierre.


Both panels contain a service disconnect, both panels must be bonded.

Here is a graphic that shows the bonding, of course you may not have a trough but you can ignore that part of it.



You can choose to run one GEC based on the 400 amp service conductors than tap it at the panels based on the 200 amp service conductors feeding each panel. 250.64(D)



[This message has been edited by iwire (edited 01-18-2005).]

I have installed a "400amp" underground service as we call it with two 2inch PVC conduits with a 4/0 URD aluminum triplex in each pipe. Come up to the 320 meter and use dual lugs to terminate. Then come out of the back of the meter can with two 4/0 aluminum SEU cables and drop into the basement into two 200amp main breaker 40 circuit panels.

For the GEC, I run #2 copper from 1 panel to the street copper water pipe.I then tap the #2 copper above where it enters the 1st panel with #4 copper and ground the 2nd panel. I also install 2 ground rods outside and run #4 copper into the meter can for the supplimental grounding electrode. Enclosure bonding is achieved by tighting the green bonding screw inside the main panels.

I have seen the above described installation with a #4 copper GEC run from each panel over to the water pipe.But I interpet Note #1 under table 250.66 to mean we are to add the circular mill area of the two sets of 4/0 URD feeding the meter can together and then base the size of the GEC by that figure.

So from table 8 in chapter 9, 211600 x 2= 423200 CMA...table 250.66 calls for a #2 GEC.

400amp service?...more like two 200amp services.

shortcircuit

My bad.

Thanks for pointing that out. My understanding was 1 bond screw per service but it's really service disco. I do remember having to take out the second panel screw to make an inspector happy a long time ago and just did it like that sence. I would say they were still bonded six ways to Sunday but it was missing the screw on the second.

Bob,

Here in NJ we do the same thing with the "400" amp meter pan.

BTW do you see Gary or Andy? The guys from Cedar Crest? If you do, tell them I quit that job.

You quit???

I hope all is well for you.

Gary is running another large housing complex close to home right now, I last saw him at the adult xmas party.

Andy? I can not think of who that is right now.

Sean is around I saw him at the Kids xmas party being a good Dad.


Bob

In my neck of the woods, for single phase services, anything 200A and less is straight through metered (usually with a 200A meter). Over 200A, a CT meter system is used (usually a pole system serving a farm, but I know of one residential CT metered service).

Shortcircuit


You don't want to call it two services, that NEC would not allow it.

Not two 200 amp services of the same characteristics. 230.2

Bob

Oops...your right Bob. How about 360amp service with two 200amp disconnects

shortcircuit

I am glad you knew I was just joking around, what you describe does sound very close to two services on one meter.

Bob