wire sizing 400 amp residential

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Stevenfyeager

Senior Member
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United States, Indiana
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electrical contractor
Its been a long time since I did an overhead 400 amp (all the POCOs around here call it a 320 amp actually) residential service. The meter base has double lugs line side so I intend to parallel the riser conductors with 4/0 AL in a 2 1/2 " riser. (with (2) 2\0 neutrals) Serves (2) 200 amp service panels. 3" riser necessary ? Does this sound correct ? Estimating stage. Thank you.
 
Stevenfyeager said:
Its been a long time since I did an overhead 400 amp (all the POCOs around here call it a 320 amp actually) residential service. The meter base has double lugs line side so I intend to parallel the riser conductors with 4/0 AL in a 2 1/2 " riser. (with (2) 2\0 neutrals) Serves (2) 200 amp service panels. 3" riser necessary ? Does this sound correct ? Estimating stage. Thank you.
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You should get a spec sheet from your POCO because they can require what they want.

I have 5 POCOs to deal with, and they are not all the same
 
Throw a little fly in the ointment.. I don't believe parallel, 4/0s in one conduit will meet the required ampacity once derated.
 
augie47 said:
Throw a little fly in the ointment.. I don't believe parallel, 4/0s in one conduit will meet the required ampacity once derated.
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So you're saying that 240.4(B) doesn't apply when 310.15(B)(7) is used, because 240.4(B) refers to the ampacity of the conductors, while 310.5(B)(7) just refers to the rating of the service? The ampacity in the example would 328A, for a service rating of 395A.

Cheers, Wayne
 
400 amps * .83= 332 amps conductor- which is necessary for the 400 amp service on a residence. You would have to de-rate 80% because of the number of conductors in a conduit. 4/0 aluminum is good for 205 amps at 90C--- 205 * 2= 410.... 80% of 410= 328 which is what Wayne had.

Since you need conductors good for 332 amps then IMO, 4/0 is not enough but if the power company has the say in this who am I to argue
 
Dennis Alwon said:
400 amps * .83= 332 amps conductor- which is necessary for the 400 amp service on a residence. You would have to de-rate 80% because of the number of conductors in a conduit. 4/0 aluminum is good for 205 amps at 90C--- 205 * 2= 410.... 80% of 410= 328 which is what Wayne had.

Since you need conductors good for 332 amps then IMO, 4/0 is not enough but if the power company has the say in this who am I to argue
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I agree if the portion of the installation that has the parallel #4/0's is subject to the NEC then the conductors are too small. You really need to know the calculated load.
 
Just had to comment...
400A residential? I would hate to have to pay that power bill. Is electricity dirt cheap in Indiana? Here in Calif. we are going to be pushing 40 cents/kWh pretty soon.
 
If you wish to avoid calculations, etc, you could parallel 250kcmilAL which would still be allowed in a 3" rigid riser;
 
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Jraef said:
Just had to comment...
400A residential? I would hate to have to pay that power bill. Is electricity dirt cheap in Indiana? Here in Calif. we are going to be pushing 40 cents/kWh pretty soon.
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Thank goodness for TVA. TVA rates < 10 cents per kwh.
400 amp residential services are farily common.
 
Jraef said:
Just had to comment...
400A residential? I would hate to have to pay that power bill. Is electricity dirt cheap in Indiana? Here in Calif. we are going to be pushing 40 cents/kWh pretty soon.
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I have done a few 600 amp services for residences. You get all electric in a large home plus 2 car chargers at 50 amps each along with pool, hot tubs etc and it can calculate up there. One house we did had 5 heating systems....

I may have been able to get by with a 400 amp service but it would have been close and with some customers you know you have to figure there will be more.
 
Jraef said:
Just had to comment...
400A residential? I would hate to have to pay that power bill. Is electricity dirt cheap in Indiana? Here in Calif. we are going to be pushing 40 cents/kWh pretty soon.
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I had a stretch when I was doing new houses, everything I did for 2-1/2 years had a six hundred amp service. Houses were 6000 - 10000 square feet.

The last I did a calculation on my electric bill, it came out to about $0.17
 
Jraef said:
Just had to comment...
400A residential? I would hate to have to pay that power bill. Is electricity dirt cheap in Indiana? Here in Calif. we are going to be pushing 40 cents/kWh pretty soon.
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Wow....just got our bill...11.06 cents per kWH, including all taxes and fees. The actual power is about 4.25 cents and the delivery change is about 3 cents. (downstate IL)
 
Service conductors are required to be sized not less than maximum load to be served. 230.42.
 
Dennis Alwon said:
400 amps * .83= 332 amps conductor- which is necessary for the 400 amp service on a residence. You would have to de-rate 80% because of the number of conductors in a conduit. 4/0 aluminum is good for 205 amps at 90C--- 205 * 2= 410.... 80% of 410= 328 which is what Wayne had.

Since you need conductors good for 332 amps then IMO, 4/0 is not enough but if the power company has the say in this who am I to argue
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You are the Electrician who is responsible for compliance with the National Electric Code for anything on the premise side of the demarcation point. In most areas the demarcation point, which is set by the State's utility regulatory agency, is the splices between the drop and the Service Entry Conductors. Since the conductors in the mast are, by definition, Service Entry Conductors that mast is NEC all the way and what the POCO thinks is OK with them is of absolutely no import. I have seen POCO staff and AHJ inspectors nose to nose over this a few times and the POCO fella always lost the argument. POCO staff often believe that everything up to or down to the meter is governed by the National Electrical Safety Code but in most jurisdictions they are wrong.

--
Tom Horne
 
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