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400 amp service

rnsykes's picture

This is a follow up to my riser diagram question.  The builder I am drawing for is using a 400 amp service coming underground.  He plans on splitting the service and running 200 ams in the house and 200 amps in his barn.  my question is this.  Comming up from the ground with a 400 amp service, what size wire will it be.  I know that the 200 amp will be 2/0.  Is it correct that the service will come up from the ground, directly into a meter, then go into a dissconnect?  then from there will branch off to the two sperate 200 amp services?  Will there need to be 2-200 amp disconnects?  What size conuit will the 400 amp cable be in, and what size do you use for the 2/0?  As a designer, this is new to me.  I'm used to it coming off a pole, going to a meter, and right in to the panel in the basement, no disconnect, no conduit, nothing.

(post #113882, reply #1 of 8)

You need to check with the POCO. First, typically they supply that run from the transformer, but it veries from POCO to POCO. They don't have to follow NEC and they don't when it comes to wire size. Also a good chnace that it will be AL.

Typically a meter with double lugs is installed and two panels or disconnects are installed side-by-side.

Depending on the details of the layout for the house you might want to install a small panel (in terms of breakers) to supply near by heavy loads, AC, pool, spa, and then run a cable into the house for to sub-panel for the main household loads.

Also not that the the 2/0 CU for a 200 amp feeder cable ONLY for residential feeder loads.

The local inspector not not allow it for a barn. Not know what the "barn" is, but in most cases it will be a much much load than that.

If you can't treat it as a residential load you need to go to 3/0 CU for 200 amps.

You might want to go to 100 or 150 for the barn (#3, 1/0)

A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
. William the Geezer, the sequel to Billy the Kid - Shoe

(post #113882, reply #2 of 8)

Thats a good point about the 150 for the barn.  The guy builds pole barns for a living, and he will keep his equipment in there I'm assuming.  I don't think he will be using it for livestock, but I guess you never know.  I'll show it as 3/0, and tell him to consider down-grading the service for the barn.  thanks for you help.

(post #113882, reply #3 of 8)

A 400 amp circuit typically requires 500MCM wire, but as Bill pointed out the power company won't necessarily follow Code for the size of the service entrance cable.  Depending on the situation, sometimes two sets of 3/0 in parallel will be used, since 500MCM is so thick and hard to work with.  edited to add:  this is for copper wire, aluminum will be larger.

Also, I'm not that familiar with residential work, but I think in most cases the utility actually uses a 320 amp meter.

Edited 2/5/2007 3:25 pm by Stuart

(post #113882, reply #4 of 8)

Alright, thanks for the responses.  I'm going to show it with a label that says "provided by utility company."  that way it's on them.  I did see somthing about a 320 amp meter on Atlantic City Electric's website, but they also had 400 amp meters, so I'm assuming that they can use that.

Edited 2/5/2007 3:51 pm ET by rnsykes

(post #113882, reply #5 of 8)


When we ran a new 200A underground service to our lake house, the co-op required and supplied 4/0 AL triplex. Was this overkill, or did the use of AL require the upsize?

(post #113882, reply #6 of 8)

4/0 is the standard size for 200 amp residential feeder. That what you need to use on your side.

A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
. William the Geezer, the sequel to Billy the Kid - Shoe

(post #113882, reply #7 of 8)

I don't know about AC but in our part of NJ (PSEG) 400 amp service incurs 'standby charges' (additional monthly charges) by the very nature of the service size.   He may absolutely need 400 amps by his loads but should check to see - up to 320 amps there are no standby charges (here).

By the way ... the local utilities use a '320A class meter pan' (double lug plug in) for up to 320 amp service I believe.  At 400 amp service they usually require a CT cabinet.   In some locales you cannot 'split' 400 amp service to 2 conduits but must bring it in a single 3 1/2" or 4" conduit.



Edited 2/5/2007 6:34 pm ET by Jeff_Clarke

(post #113882, reply #8 of 8)

Thanks for the response.  I think he is planning on bringing in a single 400 amp service, but I wondered about the conduit sizes for the 200 amps going back out of the disconnect to his barn, and the other one going into the house.