What does ‘double-tapped neutral’ mean?

As a home inspector in the Stillwater area, I often identify electrical problems as “Hazardous”, and recommend repair by qualified electrician. A common, yet poorly understood issue is double tapped neutrals, where there are more than one white wires connected to the panel using only one screw.

This blog is to explain why this is an issue.

The different colors of electrical wires indicate the function of the wire, with black and red indicating the wires carry electric current, white usually indicating neutral charge and green or bare indicating the wire is grounded.

The neutral wires and the black and red wires need to have one screw per connection inside the electric panel. More than one wire per screw could lead to arcing. Arcing is another word for sparks, meaning fire and shock hazard.

More than one white wire under one screw can create problems, but not for the same reason. If the white wires touch each become disconnected from the serial buss that they were originally connected to,other they could actually become more hazardous.

It’s a little complicated, but since you’re read this far, let’s go.

Let’s say you have two circuit breakers that bring power to you kitchen. Lets call them “light” and “microwave”.

The one we call “light” is a 15 amp breaker. “Microwave” is a 20 amp breaker. For the sake of simplicity, let’s use 12 gauge wire for both circuits. (What’s that? Yes. You can use  thick wire for low amps. You can’t use thin wire for high amp. Jeeze, this was supposed to make it easier).

Okay. we have two plastic-wrapped sets of wires running through the walls from the kitchen to the panel. We call these “Romex” or “NM” cables. Because we’re using 12 gauge wires, the outer cover is yellow. (If you really don’t have anything to do all day, go ahead and click here to learn what the colors mean.)

Because the cables have 3 wires each, you should see 2 black wires, 2 white and 2 bare. You know that the bare ones are ground, right? We only need them if something goes wrong. They go on the grounded serial buss. The black ones each have their own circuit, which is pretty easy to understand. Each circuit has it’s own breaker. If a “fuse blows”, the breaker is tripped, and has to be reset to restore power to the light or microwave.  I know you know all this.

It becomes more interesting when we get to the white “neutral” wires, because our houses are powered by alternating current, as opposed to direct current. In AC, power goes back and forth very fast (60 times a second. Usually. Don’t overthink this part).

If you took the 120 volts from “microwave” and added it to the 120 from “lights” you would have 240 volts. That’s what would happen if you connected the white wires to each other, but didn’t ground them, because the black wires would be touching each other, through the white wire!

Likely? No. Deadly? Yup.

Want to know more? (really?) Click  here.