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?
Best Answer
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.