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Sub panel wiring w/ 3 wire feed.


Brandon Whitmore
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Today's house had a sub- panel in the crawlspace, with the service equip. panel in the garage above. The GEC ran to a ground rod in the crawlspace, so instead of running a 4 wire feed, a 3 wire feed (2 hots and neutral) was run to the sub- panel, and then a ground wire was tied into the GEC near the rod. The neutrals and grounds were separated in the panel.

Is this a legit installation? I can't think of any reason why not, but I can't say I've run across it before. I've searched my house, and my code book is nowhere to be seen. I guess I should quit trying to organize things.

Any help would be appreciated.

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Today's house had a sub- panel in the crawlspace, with the service equip. panel in the garage above. The GEC ran to a ground rod in the crawlspace, so instead of running a 4 wire feed, a 3 wire feed (2 hots and neutral) was run to the sub- panel, and then a ground wire was tied into the GEC near the rod. The neutrals and grounds were separated in the panel.

Is this a legit installation? I can't think of any reason why not, but I can't say I've run across it before. I've searched my house, and my code book is nowhere to be seen. I guess I should quit trying to organize things.

Any help would be appreciated.

The first problem that comes to mind is 300.3(B):

(B) Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B)(1) through (4).

I don't see anything in (1) through (4) that would apply to what you've described.

- Jim Katen, Oregon

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Thanks Jim,

Say this sub panel is 10-15 years old. Can I assume that this installation wasn't allowed then as well?

That rule first appeared in that form in the 1987 edition.

Just to help me remember this, can you give me an idea as to what problems could occur as a result.

I don't know that anything bad would happen if the system just stayed the way it is. What would happen if someone decided to install a new & better grounding electrode at the main panel someday?

- Jim Katen, Oregon

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ok couple questions

was the feed to this sub panel ran in metallic conduit or was it a cable?

Was the grounded ( neutral) conductor insulated or bare ?

You are dealing with a feeder.

YES you are required to run the grounding conductor with the other conductors, unless it is in metallic conduit. If it is ran in metallic conduit

(rigid /emt) the conduit can serve as the grounding means.

Either way the grounded ( neutral) conductor must be insulated as well as isolated

The size of the ground is found in NEC table 250.122 (equipment grounding conductor) and is based on the size of the feeder's overcurrent protection.

Just running a wire to a ground rod will not provide the fault clearing capability needed to clear a phase (hot)to ground fault.

I have proven this by taking a live conductor with one end stripped back about 1" and the other on a 20 ampere breaker that is turned on.

I stuck the bare end in the ground and wiggled it around. Then pulled it out and put my meter on it and read voltage. It did not trip. I did this to prove to an apprentice electrician that the earth is not a good path for clearing faults.

The feeder should include:

the 2 phase conductors(hots)

a insulated grounded conductor (neutral)

a grounding conductor

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Hi Jack,

I had a big reply with quotes all written up, but my fat fingers were and are typing on a friggin half sized keyboard. Needless to say, I'll do a shorter post so I don't end up losing the info. again.

I'm not in the office, so I can't pull up the pictures to be sure I am giving the correct info., but I'll try.

It was a cable feeder with no conduit, so there is no ground for the conduit. The ground that was run from the sub panel was the same size as the GEC , which was the typical large stranded copper ground wire--- I'm not sure what size they are.

I believe that the neutral wire was not individually insulated, but just protected by the sheathing. I'm not exactly sure when this panel was added...

Thanks..

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