400 amp service, 2 parallel feeds, 2 or 1 neutral going back to transformer from meter?

H

Hofebrand

Member
Location
Montana
Occupation
Electrician
On a 400 amp meter main service, I used two 4/0 aluminum parallel feeds for my hot conductors, from transformer to meter base.(i have to supply my own wire on a 400 amp service here in MT.) With each feed i have a neutral as well, so that's 2 neutrals going from meter to transformer. I asked my power company and they said it's fine but that I only needed one neutral going back to transformer from service. could you please do a video or explain the situation. thank you 😊
 
Here is the 400 amp service with parallel feeds.
5da5785bc498d21c97cdeea5cded47f9.jpg


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Dennis Alwon said:
I have no idea why the power company said only one neutral. That doesn't make sense unless you sized the one neutral appropriately.
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But if, in fact, the calculated neutral load is half of the ungrounded load, and you are pulling all the wires in a single conduit with the resulting derating accounted for, you could pull 2 conductors per ungrounded leg and just 1 conductor for the neutral. Yes?

Cheers, Wayne
 
This is obviously a single phase application, but when running 2 parallel feeds as I installed it, shouldn't there be a neutral accounting for each feed as shown in image?? Thanks

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wwhitney said:
But if, in fact, the calculated neutral load is half of the ungrounded load, and you are pulling all the wires in a single conduit with the resulting derating accounted for, you could pull 2 conductors per ungrounded leg and just 1 conductor for the neutral. Yes?

Cheers, Wayne
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Wayne, so your saying if I used let's say two, 2 inch conduit for each feed I would have needed a neutral for each feed? In the application i used a single 3 inch conduit with all the conductors in that. To clarify I only needed 1 neutral for that particular application then?

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Hofebrand said:
Wayne, so your saying if I used let's say two, 2 inch conduit for each feed I would have needed a neutral for each feed?
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Yes, per 2020 NEC 300.3(B)(1), you need to have a balanced set of conductors in each raceway.

Hofebrand said:
In the application i used a single 3 inch conduit with all the conductors in that. To clarify I only needed 1 neutral for that particular application then?
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Yes, with only one raceway, there's no need to coordinate the parallel'ing details between different legs/neutral, so the load calc will dictate what you need. For a crazy example, on a 3P4W 240V/120V delta (high leg delta), depending on how the load calc works out, you could use 2 conductors for the high leg, 3 conductors for the other ungrounded conductors, and 1 conductor for the neutral. [Maybe that's not so crazy, since that's what you get if you overlay a 2 set 3P3W supply with a 1 set 1P3W supply.]

BTW, with 4 CCCs in the conduit, each 4/0 Al is good for 205A * 0.8 = 164A if no temperature correction is required. So if there is a single service OCPD, it would need to be 350A or less. [Even on a residence with the 83% factor, 164*2/0.83 = 395A, too low for a 400A OCPD.] If you have two separate service OCPDs, they would each need to be 175A or less. Unless of course an exemption from derating applies, like less than 24", or less than 10' and less than 10% of the total run, where in the rest of the run you do separate out into fewer than 3 CCCs per conduit/cable.

Cheers, Wayne
 
wwhitney said:
Yes, per 2020 NEC 300.3(B)(1), you need to have a balanced set of conductors in each raceway.


Yes, with only one raceway, there's no need to coordinate the parallel'ing details between different legs/neutral, so the load calc will dictate what you need. For a crazy example, on a 3P4W 240V/120V delta (high leg delta), depending on how the load calc works out, you could use 2 conductors for the high leg, 3 conductors for the other ungrounded conductors, and 1 conductor for the neutral. [Maybe that's not so crazy, since that's what you get if you overlay a 2 set 3P3W supply with a 1 set 1P3W supply.]

BTW, with 4 CCCs in the conduit, each 4/0 Al is good for 205A * 0.8 = 164A if no temperature correction is required. So if there is a single service OCPD, it would need to be 350A or less. [Even on a residence with the 83% factor, 164*2/0.83 = 395A, too low for a 400A OCPD.] If you have two separate service OCPDs, they would each need to be 175A or less. Unless of course an exemption from derating applies, like less than 24", or less than 10' and less than 10% of the total run, where in the rest of the run you do separate out into fewer than 3 CCCs per conduit/cable.

Cheers, Wayne
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Thank you Wayne for the detailed explanation. Yea It's less than 10 feet and there are 2 OCPD disconnects in this panel. 200 amp each. That's why I needed the initial 400 amps..

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Hofebrand said:
Yea It's less than 10 feet
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That wouldn't be enough in and of itself, but I see that my last post was off the mark. I was thinking these conductors were between the meter and the separately enclosed service OCPD(s). But these conductors are on the line side of the meter and carry the entire load on the service.

So the upshot is you have installed a 328A service, or a 395A service if it supplies just a single dwelling unit per 310.12. With multiple service OCPD, the size of the service conductors common to them need not be related to the sum of the service OCPDs. But your total load calc still needs to be less than either 328A or 395A.

Cheers, Wayne
 
wwhitney said:
That wouldn't be enough in and of itself, but I see that my last post was off the mark. I was thinking these conductors were between the meter and the separately enclosed service OCPD(s). But these conductors are on the line side of the meter and carry the entire load on the service.

So the upshot is you have installed a 328A service, or a 395A service if it supplies just a single dwelling unit per 310.12. With multiple service OCPD, the size of the service conductors common to them need not be related to the sum of the service OCPDs. But your total load calc still needs to be less than either 328A or 395A.

Cheers, Wayne
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That is correct. They are on the line side of the meter. So just to clarify, the image i provided of the install, the is correct right?? Thank you guys so much for the help, really appreciate it!!

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If those are 4/0 conductors in one conduit then the original poster has 4 current carrying conductor's which means 80% de-rating. Parallel 4/0 are rated 205 at 90C

205 x 2 = 410 x .8 = 328 amps

400 amp service x .83 = 332 amps-- conduct size needed for a residence at 83%

How are the 4/0 conductors compliant?
 
Dennis Alwon said:
How are the 4/0 conductors compliant?
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With multiple service disconnects, 230.90 Exception 3 says that the sum of the OCPDs can exceed the rating of the service conductors. So the only question is whether the calculated load on the conductors is no more than 328A, or 395A if 310.12 applies.

Cheers, Wayne
 
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