I have 20 Amp power run to part of my house. The conduit that carries it runs down one of the walls of my garage. I've cut the conduit, inserted a metal junction box, and intend on putting in a single 20 amp outlet in my garage for power tools, etc.
The conduit carried four wires: blue, yellow, gray, gray. As it turns out, I'd thought about this as I turned off two breaker switches, but yes, the conduit is actually carrying two 20 amp circuits. I cut the wires too quick without thinking about it though, and now find myself wondering if it matters which power is matched with which neutral.
I tested by installing the outlet with yellow, and one of the grays, and turned the breakers on (and off) one at a time. I thought that if a lamp plugged in to the outlet turned on, I would have my match. Problem is, I know which breaker is for yellow and blue respectively now, but the lamp works with either neutral.
Given that this is two distinct circuits, AND one of the circuits powers a room with expensive electronics, I'm paranoid.
So, does it matter which neutral is connected in pair with which power? If so, how do I test and figure out which neutral is which?
Best Answer
Yes, it matters. It is vital to pair the neutrals with their partner hots. You should have marked the wires at the time you installed them, either by tagging the wires with tape, or by bundling the pairs with tape, or any other method that makes sense.
Now, your best bet is to document carefully which outlets are on which hots. Then, pull one of the neutrals off the neutral rail and insulate it. Make sure that all the outlets on one circuit do work, and all the outlets on the other circuit do not work. Now you know the still-connected neutral is associated with that hot. Mark it!
Do not allow a situation where some outlets on hot A return on neutral A, and other outlets on hot A return on neutral B. That is a wiring defect that should be corrected ASAP because it will result in the neutral being overloaded. Neutrals do not have circuit breakers, so the system absolutely depends on neutrals not serving two hots.