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Old 03-04-2018, 10:21 PM   #1
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Nuetral Wire size


For my personal education, please explain the difference in these two MHF cables (mainly the difference in the neutral and ground sizes and why each variation is produced).

2/0-2/0-2/0-1

2/0-2/0-1-4

Under what cirumstances is the larger neutral required?

Installing in U/G conduit going 300 feet from 200 (240v) amp main to 100 amp sub in shop. Basic power tools, lights small air compressor maybe a small fridge. Will almost certainly never run the full 100 amps.

Do I have to have the 2/0 neutral or can I use the 1 gauge?
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Old 03-04-2018, 10:30 PM   #2
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Re: Nuetral Wire size


What is MHF cable?
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Old 03-04-2018, 10:34 PM   #3
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Mobile home feeder
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Old 03-04-2018, 10:39 PM   #4
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Re: Nuetral Wire size


Neither one is adequate for 100 amps unless the conductors are copper.
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Old 03-04-2018, 11:21 PM   #5
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Re: Nuetral Wire size


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Neither one is adequate for 100 amps unless the conductors are copper.
Huh? 2/0 AL or CO are both major overkill for 100a. It's rated at 135a for AL and 175 for CO.

Why are you using mobile home feeder cable? Why not just run individual XHHW-2 wires in the conduit? Why pay for the extra expense of a cable assembly? Or if you use direct burial cable, then why run the conduit continuous underground? You only need to sleeve it as it emerges from grade to the minimum burial depth of 24".

For 100a you need #3 CO or #1 AL and a #8 CO or #6 AL ground.

Also be sure to install a separate ground bar in the sub panel and do not bond the neutral to the enclosure with the green screw or copper bonding strip. You also need to install a supplementary ground rod with #6 CO and terminate it on the ground bar because it is a separate building.

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Old 03-04-2018, 11:24 PM   #6
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Re: Nuetral Wire size


You need to use a full size neutral. The MHF has a version with a smaller neutral because it is meant to serve an entire dwelling unit where it is sometimes possible to reduce the neutral size. This is not the case with your outbuilding.

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Old 03-04-2018, 11:27 PM   #7
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Re: Nuetral Wire size


I just now noticed that your run is 300 feet. Did you oversized this cable to compensate for voltage drop? Or did you just not know what size cable you needed? Regardless it would be a good idea to oversize the cable for such a long run.

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Old 03-05-2018, 06:43 AM   #8
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I had an engineer from electric company come out and see about setting a new pole down by the shop. He's the one who suggested the mobile home feeder wire in lieu of a new pole because I have the 200 amp main and currently only run 75 amps at peak. Using the online calculators, It seems like the 2/0 is borderline on the wrong side with the voltage drop at 300 feet. I figure 4/0 would be best but would rather avoid the added troubles of the 4/0 if I can.
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Old 03-05-2018, 07:15 AM   #9
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Re: Nuetral Wire size


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Originally Posted by mr_robot View Post
Huh? 2/0 AL or CO are both major overkill for 100a. It's rated at 135a for AL and 175 for CO.

Why are you using mobile home feeder cable? Why not just run individual XHHW-2 wires in the conduit? Why pay for the extra expense of a cable assembly? Or if you use direct burial cable, then why run the conduit continuous underground? You only need to sleeve it as it emerges from grade to the minimum burial depth of 24".

For 100a you need #3 CO or #1 AL and a #8 CO or #6 AL ground.

Also be sure to install a separate ground bar in the sub panel and do not bond the neutral to the enclosure with the green screw or copper bonding strip. You also need to install a supplementary ground rod with #6 CO and terminate it on the ground bar because it is a separate building.

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You are correct. I misread the post as 2/2/2. My bad.
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Old 03-05-2018, 07:18 AM   #10
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Re: Nuetral Wire size


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Originally Posted by 10022089 View Post
I had an engineer from electric company come out and see about setting a new pole down by the shop. He's the one who suggested the mobile home feeder wire in lieu of a new pole because I have the 200 amp main and currently only run 75 amps at peak. Using the online calculators, It seems like the 2/0 is borderline on the wrong side with the voltage drop at 300 feet. I figure 4/0 would be best but would rather avoid the added troubles of the 4/0 if I can.
Be advised, 4/0 conductors will need to be reduced in size at the termination points as they will not fit into a 100 amp breaker.
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Old 03-05-2018, 07:24 AM   #11
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yea that's one of the troubles I'm hoping to avoid by using the 2/0. So will the 2/0 be ok and I have to use th 2/0 neutral as well?
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Old 03-05-2018, 07:29 AM   #12
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Re: Nuetral Wire size


If you made the feed breaker 80A's then 2/0 AL would be fine with 300' run.
Still plenty of power for what you want to do.
Wouldn't suggest reduced neutral.
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Old 03-05-2018, 10:32 AM   #13
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Re: Nuetral Wire size


4/0 is overkill. 2/0 would work fine. You'd have to order an 80a breaker from a supply house as they are not available at home depot, Lowe's, etc.

I would just use a 100a breaker. The breaker has nothing to do with voltage drop. It's the actual connected load that makes the difference.


The neutral needs to be the same size as the ungrounded conductors unless you can show that you have a reduced neutral load, perhaps due to a majority of 240v equipment, but why bother? I am not a fan of reducing neutrals simply because of the levels of harmonic currents in modern equipment and electronics.

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