Switch Has Neutral

Identifying the Neutral Wire - Updated January 17, 2026

Dear Mr. Electrician:  How do I know if my existing wall switch has a neutral wire inside the electrical box?

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Answer:  The wall plate would need to be removed to see if there is a neutral inside the switch box.  If you see a white wire attached to the switch and no other white wires inside the switch box, it is very likely there is no neutral wire.  The photo at the top is an example.  That switch controlled the electrical receptacle outlet below.

DOES THE SWITCH HAVE A NEUTRAL WIRE

An ivory electrical receptacle with a painted face is hanging by a black wire, two white wires, and two bare copper wires. There is a yellow wirenut at the top of the photo with two black wires and one white wire joined together. That white wire is the LINE wire for the wall switch that controls this outlet.
An ivory electrical receptacle with a painted face is hanging by a black wire, two white wires, and two bare copper wires. There is a yellow wirenut at the top of the photo with two black wires and one white wire joined together. That white wire is the LINE wire for the wall switch that controls this outlet.

If you want to see how a switch without a neutral can be changed to a hot and a neutral, read my article with photos here.

In addition to visually inspecting for a neutral wire, it is possible to test the wires with a non-contact voltage tester, a CAT III voltmeter, or a pigtail socket with a light bulb.  However, this must be done with the electricity on and there is a risk of electric shock or electrocution.

An electrician might use electrical gloves when doing this type of test.  A non-contact voltage tester is the easiest method but can also give false readings, especially on wires with old insulation.  Also this tester only reads live LINE wires.  It doesn’t test for neutral or a LOAD.

Just touch each wire with the tester to see if you get a reading.  If multiple wires are connected, they would need to be separated.

With a CAT III volt meter the probes can touch each wire and see where the meter gets 120 volts.  The grounding conductor can be used as an initial reference until the neutral is found.  Connected wires would need to be separated.  Take pictures and label the wires before taking them apart.  If the volt meter shows a much lower voltage it may be reading between LINE and LOAD.

A pigtail light bulb socket and incandescent light bulb can be used in the same manner as the voltmeter to test to see if a switch has a neutral wire.  If the light bulb lights up fully between two wires you have found the LINE and the switch has a neutral.  If the light bulb is dimly lit you have found LINE and LOAD.

Below is an older switch hanging from a metal switch box.  This switch box has a neutral wire in it.

An old electrical wall switch hanging by two black wires coming from the metal switch box inside the wall, which has a neutral wire. There are two 16D common nails passing through the upper and lower inside of the box to attach the switch box to the wood wall stud.
An old electrical wall switch hanging by two black wires coming from the metal switch box inside the wall, which has a neutral wire. There are two 16D common nails passing through the upper and lower inside of the box to attach the switch box to the wood wall stud.

Metal switch boxes were sometimes attached to the wood wall stud during house construction using very large nails that passed through the interior of the switch box.  The holes for the nails had been made at the factory and this was an approved installation method.

An older in-wall, one-gang metal switch box with three cables entering through the top inside. Three white wires are joined together. This switch box has a neutral
An older in-wall, one-gang metal switch box with three cables entering through the top inside. Three white wires are joined together. This switch box has a neutral

The above switch box was removed and a two-gang box was installed to control a new ceiling fan with a light.  CLICK HERE to read the details with photos.




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