I've seen posts about going from a switch to a dimmer, but not the other way around. I originally thought I could read those and do the opposite, but it seems that there are many ways houses can be wired, and my particular setup doesn't match anything else I have seen.

I currently have a Z-Wave dimmer switch installed. It has two black wires coming out and one green. The black wires are supposed to go to either line and load.

My new Z-Wave 2way switch has load, line, neutral, and ground. I determined that load goes to my light, line goes to whatever is hot, and ground obviously goes to ground. I figured out which was hot by turning off the circuit at the breaker, disconnecting the switch, then turning it back on again and measuring the voltage. The black wire with the 120V is line, and the black wire without 120V must be the load.

Now my issue is with the neutral -- since it wasn't previously hooked up, there is a bundle of three wire wires in the box capped off. The problem is that I don't have three entry points to the switch. I could insert 2 of the 3 into the holes, and the strip some extra insulation off of the third and wrap it around the screw (and check to make sure the other two are still tight), or I could go get some solid core wire at the store and add a fourth white wire to the capped bundle, then run this fourth to the switch.

Ultimately, my question is, shouldn't all switches and outlets have a dedicated line back to the breaker box? If neutrals are tied together in boxes, doesn't this mean that there could be two circuits are sharing the neutral? And if this is the case, doesn't that mean that working in the box is inherently not safe if the other circuit is still live? Also, does this mean that I cannot simply pull one the three white wires from the bundle and hook it up to the switch, since that would separate it from the other two, and there might not be a path back to the breaker box for one of the circuits?


If the switch has screw terminals as opposed to wire leads you DO have to pig-tail a piece of wire to the splice and then connect that tail to the switch. DO NOT place more than one wire under a binding screw terminal, unless of course it is designed for it. Even in that case it would only be designed for up to two wires.

Do you have a model number for this switch?

Regarding the neutral wires in the box, NO not every wire goes back to the breaker box. This is why you have several whites. One is a feed and the others are feed out to other items on the same circuit. If there is more than one circuit in the box then the neutrals from those different circuit should NOT be spliced. The only time this is not the case is if it is a multi-wire branch circuit (shared neutral).

  • I'm pretty sure it's this one: amazon.com/Z-Wave-Wireless-Lighting-Control-Switch/dp/…. I ended up putting two wires into the holes in the back, and then one underneath the screw. I pulled on them quite hard to ensure that there is a solid connection. Everything works! It probably doesn't matter which neutral goes back to the box, as they all need to be connected anyway so they all have a path back... but if I wanted to determine this, how would you do it? – Dave Dec 6 '14 at 15:15
  • To determine the neutral you'd have to determine which hot is the feed (done easily with a non-contact tester), and then find it's corresponding white wire. Thing is, this is not necessarily the run directly from the panel. There may be other boxes ahead of it in the circuit. – Speedy Petey Dec 6 '14 at 16:29

"Ultimately, my question is, shouldn't all switches and outlets have a dedicated line back to the breaker box?"

By modern wiring code, yes, there should be a neutral in the switch box. In older houses, that was not always the case; sometimes only the hot ran through the switchbox (especially when it was wired as a "switch loop").

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