On Jun 2, 9:41*am, N8N wrote:
On Jun 1, 8:22*pm, "John Grabowski" wrote:





"Nate Nagel" wrote in message

...

Bill McKenzie wrote:
I am trying to install a combination light/fan/heater in a bathroom.
There are already 2 sets of wires going from the switch box to the
ceiling location, but I need 3 (one for each light, fan, heater).
Would it be OK to share a single neutral for all three devices and use
the extra white wire in the second cable as an additional hot? *The
two cable are different colors (black and white) and the black seems
to have larger gauge wire than the white. *Any help appreciated.

nope. *what you need to do is run either a single 12/4 if such a thing
exists, or a piece of greenfield with six conductors in it (black, red,
blue, ?? (orange?) white and green. *Otherwise you need to split the
neutrals and replace one of your 12/2wg's with a 12/3wg. *Reason being
that all the currents in a given cable assembly need to sum to zero.

nate

The return currents only sum to zero when opposite phases are involved.

Correct.

With multiple switch conductors the sum of the neutral current will be equal
to the total load in use at any given time.

Also correct. *What is required is that the neutral current and the
sum of the "hot" currents be equal and opposite within a cable
assembly. *If the OP has two cables going to the fan and repurposes
one of the neutrals to serve as a hot, and then combines all neutrals
into one, then one of the cables will have all of its current flowing
in the "hot" direction. *(it helps to visualize this better if you
think of this as a DC circuit, even though it's not.)

nate- Hide quoted text -

- Show quoted text -

Thanks for the responses. Your explanation makes sense, Nate, but can
I ask what the risk is of having unbalanced loads in the two cables?
Is it possible this would have been allowed 30 years ago but not now?
Reason is, we have an older house (about 30 yrs) with 6 bathrooms. 5
of them have an older heater/fan/light combo, all identical and when I
take the plate off the switches they all have the same cabling: one
10/2 coming in, and a 10/2 and 12/2 going out. About 10 years ago
(before we bought it) someone took the fan out of one of the
bathrooms, leaving the old wiring in place and I want to put a new one
in. I'd really like to avoid re-wiring (it's fastened to the studs in
the wall), but I dont want to burn my house down either.