Why Are White Wires On My Light Switch
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Why White Wires are Sometimes Used for Light Switches: Wiring Light Switches with White Wires © By: Dave Rongey |
Wiring Light Switches with White Wires
Electrical Question: I am changing out a ceiling fan and wall switch.
- When I pulled the existing switch the White wires (I assume they were neutral wires) were connected to switch.
- This made me nervous and I wanted to double check which wire was hot.
- So I tested the wires – Hot to Neutral 125v, Hot to Ground 35v, Neutral to Ground 30v.
- I opened every other box I could find on this circuit and they seem OK (I checked wire nuts, screws), tested one of them and got 125volt.
- I did not find the feed wire to my fan switch in the other boxes though, it’s a blue Romex and the only ones I found were white. Any suggestions? Is this dangerous?
- Attic access to this spot is very difficult and unbearably hot in Florida during the summer even at night (trust me I did it last Sunday night).
- The previous fan installed by a previous owner was still functioning after about 20 years.
Background: Bill, a Handyman from South Florida.
Dave’s Reply:
Thanks for your electrical wiring question Bill.
Why White Wires are Sometimes Used for Light Switches
At times, we still find in some older homes that White Wires are used for wiring light switches, and the light switch wiring method is different, however we also find White Wires being used today for wiring light switches however the method is entirely different.
- Some older homes were wired where the Neutral was switched, not the hot, and thank goodness that is not the practice today.
- However many times an electrician will use a white wire as a switched leg, but when this practice is used the wire should be identified with black electrical tape.
- The 35 volt reading form hot to ground should be checked. This is sometimes an indication of a neutral feedback when one of the main power legs is lost on a 240 volt service, but this may also be an indication that the neutral wire is being switched, and you may find that when the switch is in the ON position this voltage reading will change to zero or 120 volts, factors within the circuit will affect this including the type of light bulbs that are used in the light fixture.
- This may or may not be the case with your situation, to know for sure you should have a qualified electrician perform a few tests that would reveal the condition.
More about Wiring Light Switches
Wiring a Light Switch – Diagram 1
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Hi Greg,
From what you have described the existing switch is a three way switch. White wires are often used for switching, however the white wire should then be identified with black electrical tape or a permanent marker. If the wiring does not appear to be correct then the wiring should be traced out and identified and corrections made as needed.
I hope this helps,
Dave
I was just reading this article as I also was going to switch out some old switches to more modern light switches. When I pulled out the existing switch I noticed I have 2 black wires and a white wire connected to the old switch. I tried to figure out the path of power but I wasn’t getting the readings I was expecting. The old switch had 3 screws on it. 2 light brass and 1 dark brass named “common”. The ground is screwed into the box so I understand that. The dark brass had the main power connected to it.
I tried to find continuity to the light this switch operated but I could only find it with the white wire. The black wire from the light to the light switch did not make my meter beep so I am not sure where it goes. There is also some other things in that light box I am not understanding. The switch mounting box is made for a double light switch but only has 1 switch mounted in it. It looks like the previous owner of this house just put putty over the other half. But in that box there are 3 sets of wires going into the box, there are red and white wires twisted together, white and black twisted together, and actually the main power wire going to the light switch I am wanting to change which has a black wire, white wire and a little single lead wire going to this light switch twisted together.
Why do I have white wires twisted with black wires, why is there a white wire going to this light switch? Do I have a 3 way switches in there?
Thanks Greg