Electricity is some what of a mystery to most people. All those wires can look pretty confusing and intimidating. The truth is every wire has a proper place. In a main electric panel there are only a few places where each wire belongs.
There are usually three wires in every house circuit. A hot (black or red wire), neutral (white) and ground, (bare or green). Each wire has a specific place and function. Connecting wires together that should be kept separate can have bad consequences. These may be immediately apparent, seeing big colorful flashes and sparks or latent, typically after someone gets hurt.
One of the most frequently found problems in a main or sub-panel is a defect of the latent kind. This is when the panel is not correctly grounded.
The main service panel pictured is wired wrong. It has been this way from day one, about 20 years! The panel is in a multi unit condo building.
What's wrong is this main panel is actually a sub-panel being used as a main panel. Therefore it has to be wired as a sub-panel.
What's the difference between a main panel and a sub-panel panel? The simplest explanation is feed wires. Every panel whether main or sub has main feed wires. As the name implies these wires "feed" the panel all the current for the distribution circuits.
In a main panel there are three feed wires and in a sub-panel there are four. This is a very simplified explanation. In both a main and sub panel two of these wires are hot and feed current to the panel to distribute to the branch circuits. The other common wire is the neutral. This is where it gets complicated.
In a main panel the neutral is wired to a terminal shared with the ground wires. That terminal is bonded (an electrical term meaning it is in contact with) to the panel itself.
In a sub-panel the neutral is wired to a terminal that is separate and isolated from the ground wires and the panel. That extra fourth wire is a ground which is wired to its own terminal bonded to the panel. Check the diagram for a visual explanation.
Getting back to the "main" panel in the picture. The problem is the fourth wire is connected to the same terminal as the neutral. You can see this in the upper left corner of the panel. This in effect renders the panel and the system ungrounded. This is a problem you will only know about after someone gets hurt or, as was the case here, a home inspector discovers it.
James Quarello
JRV Home Inspection Services, LLC
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