My main service panel is 200 amps and has only 2 black wires coming in, there is no neutral wire like I was told is commonly how it should be. All neutral and ground wires for the individual circuits are connected to the same bar.

My question is in regards to a sub panel that is detached from the main house, the sub panel was already installed when I bought the house. The sub panel has 2 hot wires coming in the top and a ground. All breakers in the sub panel connect their neutral wire and their ground wire to the same bar. My understanding is that if your main panel has the neutral and ground wires bounded then the sub panel must not be. In my case both the main panel has the neutral and ground wire on the same bar, AND the sub panel has neutral and ground on the same bar. Is this a problem? If I have a fault in my neutral will the ground wire be electrified?

  • Do you have grounding rods at the detached structure? NEC allows for existing 3 wire feeders and bonded neutral under the proper circumstances but rods may still be required according to 250.32. – Ian Jul 17 '16 at 13:05
  • no grounding rod at the sub panel. – Tilopa108 Jul 17 '16 at 17:43
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    That is correct, if your neutral floats, any connected load will lift neutral (and therefore the connected grounds) toward 120V. And, putting in a ground rod for the sub-panel will not help, and will make things worse insofar as creating the illusion of protection. I would hasten to put a GFCI breaker in the main panel as a short term band-aid. – Harper Jul 18 '16 at 0:22
  • When you say "panel" do you mean the phase buses themselves or the entire (enclosure) box and the phase buses all as one? – Copenhegan Apr 18 '18 at 11:49

Up until 2011 the National Electrical Code allowed a "3 wire" method of connecting a sub-panel. This means you have the two "hot" wires and a neutral running to the sub-panel as opposed to the "4 wire" method where you add a separate equipment ground wire.

So, when your house was built, it was perfectly legal to use the 3 wire method. There is no problem with this unless you connect a metal pathway, such as a water pipe, from one building to the other. This allows neutral current to flow on this parallel path. This could be potentially lethal to someone working on the pipe.

As to the main panel not having a neutral: it does. If you look again you will see the two hot wires and a bare conductor. There is no ground wire on the service drop. The bare conductor is the neutral. This is allowed on the service drop, but from that point on all neutral conductors must be insulated. Ground wires are always allowed to be bare.

So, in short, there is no problem with your system unless you run a metallic system to the sub-panel building. This would create a problem.

  • Just so I understand you, the sub-panel does not have a 3-wire. From the main panel there is a 50 amp 2-pole breaker with a 10 gauge 2-wire connecting it to the sub. So, 2 hot wires from the breaker and a bare ground go into the sub. Is this ok? – Tilopa108 Jul 17 '16 at 17:49
  • The bare wire to the sub panel is still your neutral; it will carry some current. However, I don't think it was ever legal to run a bare neutral to a sub panel or appliance. I would contact your local inspector about this and any grounding rod requirements. – Ian Jul 17 '16 at 22:48
  • What if he installs a parallel and separate actual-ground wire? – Harper Jul 18 '16 at 0:23
  • He would need to run an insulated neutral wire and then isolate the equipment ground from neutral bus on the sub panel, like the typical 4 wire feed setup. – Ian Jul 18 '16 at 1:28
  • And since you can't run a neutral separate from the hots, that really means a whole new cable run... Ouch. – Harper Jul 18 '16 at 1:50

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