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#96411 - 11/24/05 11:15 PM USE Cable sizing 400A  
dinotats  Offline
Joined: Aug 2003
Posts: 11
Fox Lake, IL usa
I've recently took over a job started by someone else. A 4500 sq single family with a 400A Underground Meter pedestal with Main CB's.

The power pole is 120' away and power is currently temporarily provided by a pre-existing overhead drop that's nailed to the house and tucks in under the meter.

A 4" PVC was placed in the ground by the GC to run Conductors underground from the pole to the meter.

"NOW my question is does Article 310.15 (6) apply to the cable leading from the pole to the meter. I want to use 500mcm triplex aluminum I don't see where in the code book says it's rated for 400A but at the supply house the wire says suitable for 400A but I sort of don't believe it. Otherwise I'm using 500mcm copper.

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#96412 - 11/24/05 11:47 PM Re: USE Cable sizing 400A  
George Little  Offline
Joined: Jan 2004
Posts: 1,489
Michigan USA
If you are feeding a single circuit breaker than I'd agree with your approach. On the other hand, if you are supplying more than one main and you did say "CB's" then the smaller conductors are okay as long as they will handle the load based on the calculations in Article 220. I base this statment on what it says in Article 230.90(A) Exception #3.

I might add, I don't understand your reference to using triplex if conduit is being used??

[This message has been edited by George Little (edited 11-24-2005).]

George Little

#96413 - 11/25/05 07:25 AM Re: USE Cable sizing 400A  
dinotats  Offline
Joined: Aug 2003
Posts: 11
Fox Lake, IL usa
thanks for responding.

The total load calculation for the house is about 325A right now. The cables will terminate into 1 lug each. then power passes through the meter and the meter itself feeds 2 individual 200A 2pole breakers.

And what I'm trying to say is this part of the work is the supply to the house which is normally handled by the power company, but because the pole is located on private property they charge a lot to install any cabling to the house. The homeowner wants me to do it and charge less of course.

#96414 - 11/25/05 04:04 PM Re: USE Cable sizing 400A  
PCBelarge  Offline
Joined: Jun 2003
Posts: 681
Dobbs Ferry, NY, USA
500s (al) are rated for 310 amps as per Table 310.16.

500s (al) are rated for 350 amps as per Table 310.15(B)(6).

Pierre Belarge

#96415 - 11/25/05 04:14 PM Re: USE Cable sizing 400A  
George Little  Offline
Joined: Jan 2004
Posts: 1,489
Michigan USA
Looks like you'd need nothing less than 500kcmil alum. or or 350 kcmil cu. on the line side of the meter and on the load side of the 200a mains you'd need 3/0 cu. or 4/0 alum.

George Little

#96416 - 11/25/05 04:57 PM Re: USE Cable sizing 400A  
caselec  Offline
Joined: Apr 2002
Posts: 558
San Jose, CA
It sounds like you are planning to feed this dwelling with two 200 amp feeders. You should install one 400 amp feeder to the dwelling using either 400 CU or 600 AL. At the dwelling you can install two 200 amp MB panels next to each other or a single 400 amp panel.

225.30 Number of Supplies
Where more than one building or other structure is on the same property and under single management, each additional building or other structure that is served by a branch circuit or feeder on the load side of the service disconnecting means shall be supplied by only one feeder or branch circuit unless permitted in 225.30(A) through (E). For the purpose of this section, a multiwire branch circuit shall be considered a single circuit.


Curt Swartz

#96417 - 11/26/05 12:44 AM Re: USE Cable sizing 400A  
dinotats  Offline
Joined: Aug 2003
Posts: 11
Fox Lake, IL usa
Thanks everyone for kicking in. See I've done a couple of 1200A and 400A services on these McMansions all over the north shore of Chicago. But I've never had to put The supply wire from ComEd's Pole to my meters.

I've seen them hook up to all my services with Cables significantly smaller that 500's on a 400A service. So I just don't want to goof up and have to re-pull larger cables if the AHJ says no.

So thanks all for chiming in. also take a look at this paragragh of Article 310.6

"120/240-Volt, 3-Wire, Single-Phase Dwelling Swervices and Feeders. For dwelling units, Conductors listed in Table 310.15(B)(6), Shall be permitted as 120/240-volt, 3-wire, Single Phase service-Entrance Conductors, Service Lateral Conductors, and feeder conductors that serve as the main power feeder to a dwelling unit and are installed in raceway or cable with or without an equipment grounding conductor. """FOR APPLICATION OF THIS SECTION, THE MAIN POWER FEEDER SHALL BE THE FEEDER(S) BETWEEN THE MAIN DISCONNECT AND THE LIGHTING AND APPLIANCE BRANCH-CIRCUIT PANELBOARDS(S). The feeder conductors to a dwelling unit shall not be required to be larger than their service-entrance conductors. The grounded conductor shall be permitted to be smaller than the ungrounded conductors, provided the requirements of 215.2, 220.22 and 230.42 are met.

So here's how I want to disect this paragragh.

Notice in the beginning of the para. that the code mentions three kinds of conductors

It puts a comma after each type and ends the sentence "that serve ase the main power feeder to a dwelling."

Then continues to Define the main power feeder. So by reading the difinition of feeder as stated here as going from the main disconnect (meter) to the panel boards so it doesn't count as petaining to going from the supply pole to the meter.

So if you're opposing my thoughts how many times have you gone to a house and upgraded the service from a 60 or 100 to a 200. And say it's overhead. We stick our meter on put up a riser, throw in a couple of 3/0 and "hook up to whatever is there" and the inspector will come over and check your work and hopefully check it off.

Am I making any sense?

#96418 - 11/26/05 01:09 AM Re: USE Cable sizing 400A  
winnie  Offline
Joined: Sep 2003
Posts: 649
boston, ma
Read article 90, specifically paragraph 90.2(B)(5). The NEC does not cover the equipment used by the power company to distribute electricity. In general you use NEC specified conductors from the weatherhead on down for an overhead service, and from the meter with a UG service. The service drop or service lateral are specified by the power company.

Check with the inspector to see where, _your local_ for _this install_, the boundary between NEC and POCO requirements is located. If the line from the POCO pole to the meter is considered POCO responsibility (even if you install it), then have the POCO tell you what size wires to install. If it is not POCO responsibility, then you will need to use NEC sizing.

For what its worth, POCO sizing is much stingier than NEC sizing for residential services.


#96419 - 11/26/05 02:23 AM Re: USE Cable sizing 400A  
dinotats  Offline
Joined: Aug 2003
Posts: 11
Fox Lake, IL usa

You're right up my alley there.

I knew there was something in the code which ommits Service drops and laterals from the power company

Thank You, Thank You, Thank You It's been racking my brain for a week.

#96420 - 11/26/05 11:04 PM Re: USE Cable sizing 400A  
dinotats  Offline
Joined: Aug 2003
Posts: 11
Fox Lake, IL usa

I called my AHJ and we spoke about this subject and he agreed. It's out of his authority.

We talk about the total demand load and realistically what the draw would be in the summer. He's comfortable with anything larger than 400mcm al, or 350cu.

Thanks Again

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