How White Wires are Sometimes Used for Light Switches

Question: I am changing out a ceiling fan and wall switch.

• When I pulled the existing switch the White wires (assume neutral) 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 (checked wire nuts, screws), tested one of them and got 125v, 125v, 0v.
• 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 question Bill.

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.

RESOURCES

How to Wire a Switch

Wiring a Light Switch – Diagram 1

Wiring Diagrams
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Electrical Wire for the Home

Electrical Wire for the Home

Circuit Wiring

Electrical Circuit Wiring

This article looks at common 120 volt and 240 volt house wiring circuits and the circuit breakers that are installed identifying the types and amperage sizes used in most homes.

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