Electrical – use the white from one switch, but the black from another


Some terminology, because I don't know any better:

light-fixture  - An existing, separate, light fixture...currently with dedicated 14/2
vent-unit      - A new vent just installed, has three functions:
    vent-fan        - The fan component of the vent-unit
    vent-light      - The main light component of the vent-unit
    vent-nightlight - The nightlight component of the vent-unit

I just replaced an old bathroom vent with a new one that has a light, nightlight, and fan. The bathroom also has a separate light fixture. There are two switches to control them (one for the light-fixture, one for the vent-unit), and this means there are two 14/2 cables going up into the attic (one to the light-fixture, one to the vent-unit).

The electrical diagram for the vent-unit I bought indicates that the vent-light and the vent-nightlight are tied to the same white, internally. There is a separate white for the vent-fan. The easiest way to get the vent-unit hooked up would be to tie all the blacks (one each for vent-light, vent-nightlight, and vent-fan) to the black of the incoming 14/2, and both whites (one goes to the vent-fan, and one shared between the vent-light and vent-nightlight) to the incoming white. This means that the vent-unit switch would control all three functions of the vent.

What I WANT is for one switch to control the light-fixture, vent-light, and vent-fan…and for the other switch to control the vent-nightlight. I specifically want the vent-fan to come on anytime a real light is turned on, and I specifically want the vent-nightlight to be controlled separately (since I will usually want it on regardless).

This means one switch would control lights/fan, and one switch would control vent-nightlight.

What this boils down to

My first reaction is to run the "nightlight" switch black to the vent-nightlight black, but the "lights/fan" switch white to the vent-nightlight white (since the vent-nightlight white is shared, internally, with the vent-light). Would this work? Would the fire department become unwittingly involved several hours later?


Another idea, is it safe to run the whites from BOTH switches to one termination? Could I run the "nightlight" switch black to the vent-nightlight black, the "nightlight" switch white to the vent-nightlight, AND the "lights/fan" switch white to the vent-nightlight white?


Here's an ugly picture of the situation. What I WANT is for one switch to control the vent-nightlight, and the other switch to control everything else.

The weird box thing at the bottom of the pictures is supposed to be a two-gang light switch.

Wires and Switches

Best Answer

You either have to replace the Vent wire with 14-3 AWG wire, or run a second 14-2 wire from the existing light to the vent. Assuming both switch circuits are from the same feed, you only need 3 wires to the vent. All the whites get tied to the white neutral of the feed. You could use the black (or Red) to go to the light - fan, and the Red (or black) to go to the night light.

This quick schem shows the connection with adding one 14-2 cable from the existing light to the Vent.

M-L-N can be switched around, depending on which functions go with the shared switch. I assumed the night light gets its own switch.

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