Determine Neutral Wire

(Ron Parker) #1

I wish to install smart switch in bathroom. Below is an image of my existing switch box. There is a light and heater on the dual gang switch. I am trying to determine if the white wire I see is the “neutral” wire. I tested all the wires with the power on, and the only wire which does not have power is the white one. I know you aren’t on site to give a definite opinion, but could someone render a good educated guess as to whether that white wire could be used as neutral for smart switch install? Thanks!!

( co-founder Terry @ActionTiles; GitHub: @cosmicpuppy) #2

Odds are that it is the Neutral, especially because it is white. (green or bare copper would be Ground).

One thing you might test is see if any other outlets / lights break when you cut the wire. That will prove it is a part of your AC loop.

(Ron Parker) #3

That’s what I’m thinking too. I’m going to order the smart switch and just give it a try. Thanks for response!

( co-founder Terry @ActionTiles; GitHub: @cosmicpuppy) #4

The usual but important warning applies here.

If you are not certain of the wiring, you should have a licensed electrician verify; otherwise you put your household at risk for electrocution or fire.


If you have a non-contact tester (one that lights/beeps when you have current), and the switch is off, the neutral will not trip the tester but the hot will. And by the looks of things, you should be able to get the sensor close to the neutral but not close to the hot. Just remember to also touch the hot (to make sure your tester’s batteries are working). If you don’t have one, you can pick one up at any hardware store for less than $5.

(Ron Parker) #6

I did use a non-contact tester. The way I tried it was: I turned both switches on. All the wires beeped hot except the white wire. Thank you for the suggestion. I will also try with switches off.


Wait…the white wire didn’t beep with the switch ON? That doesn’t make any sense. There should be current on the neutral only when the switch is ON, not when it’s off. Can you confirm please?
Also, you don’t detail which is the HOT wire coming in with the power. I see that you have two load wires, one for the lights and one for the heater. Also, are you planning on wiring the lights or the heather or both to a smart switch. Depending on the current draw of the heater you might need a heavy duty smartswitch.

(Ron Parker) #8

When both switches are on, both wires connected to light and heater beep. White does not.
When both switches are off, only the bottom wire on light and bottom wire on heater are hot. Top wires, and white wire do not beep. So, does this mean that more than likely the white wire is NOT neutral wire?

Yes, I do want to use switch to turn heater on/off as well.

(Daniel Ionescu) #9

Neutral is grounded at the breaker box and shows no current on a non-contact tester.

(Daniel Ionescu) #10

Check resistance between your white wire and ground. If it’s 0 or close enough, it is neutral.


When the switch is on or off? Because it will show current when there is current flowing through it. LOL

(Daniel Ionescu) #12



Exactly my point.

That’s why I questioned this comment. Try reading before you go correcting people.

(Daniel Ionescu) #14

Apologizes for trying to help. However, I said resistance, which is different from voltage.
Hace a nice day.


Actually you’re not helping me because i’m not the OP. And your snide comments do nothing to help the OP with the issue.

(Ron Parker) #16

I hope this isn’t too technical a question, but if there is no ground coming into the box, how do I check resistance between the white and ground?


I wouldn’t do any of that unless you know 100% what you are doing. You could seriously hurt yourself. And you have a metal box…that’s your ground.

(Ron Parker) #18

Got it. This appears to be far more complicated than I thought it was going to be. It sounds like I’ll need to call in an electrician, or at least someone who knows everything to know about light switch wiring. Thank you everyone for your help! I’m way more educated on this and I do appreciate it.

(Daniel Ionescu) #19

Only if properly grounded.


I am assuming the wire is to code. I think that’s a pretty safe bet in the us.