Friday, February 20, 2009

Subject: Three wire, two circuits??

Name: Matt

Question: I am looking to add outlets to a basement and have run into a problem. My panel has two 15amp circuits for the basement. One runs the lights that are there and one does nothing. We tracked the wires and found that both 15amp circuits are running in the same 3 wire line, black, red, white, ground. The existing lights are run on the black and neutral, that is on one 15amp line. The red, on its own 15amp line, is just capped off in the line. I checked with a meter and found that the this red is indeed the line to the other 15amp breaker in the panel. Can I run outlets off of this red line taping into the common neutral to complete the loop, or will I over load the neutral? Keeping in mind that the 15amp black already uses this neutral.

Answer: Hi Matt,You have found a spare circuit that was probably intended for the addition of outlets in your basement. In this type of circuit you have two hot wires. One hot Red wire and one hot black wire. They should be at different phases. That means if you testes between the two wires you will have 220 volts. If you test from either wire to the white neutral you will have 110 volts. These two wires can share one neutral because they are waves going in opposite directions and cancel each other out when they reach the neural wire.In general I do not like to run circuits this way because it is possible to spike the voltage going to your outlets and light if your neutral goes bad. A 220 volt spike will destroy anything plugged into that circuit so I don't think it is worth the risk. Since it is pre-wired it is ok to use it but if I was able to get an new circuit to the panel I would just take that red wire off the breaker and forget about it.

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