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.

On Jun 1, 12:44*pm, 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.

It's ok, that's what is usually done. Just make sure you know which
wire is which.
Are you sure the black wire is larger than the white? Both are usually
the same guage in a romex or BX wire.
You should also have a ground wire. And this device should be on its
own circuit since a heater is involved. At least 12 guage wire.

"Bill McKenzie" wrote in message
...
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.

First of all, you need a dedicated 20 amp circuit for the unit. The easiest
way to wire the unit is to run the #12/2 feed into the switch box, then get
either a piece of 12/4 cable to go from the switch to the unit, or use
flexible metal, or non metallic conduit, and pull 4 #12 conductors, plus a
ground, from the switch to the unit. Most of these units now also include a
night light, if yours does you'll need one more conductor from switch to
unit

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

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

Nate Nagel wrote:
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


Oops I meant five conductors. I was getting your post confused with one
from very recently. That poster was using a fan/heater/light/night
light combo.

nate

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

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

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

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.

Bill McKenzie wrote:
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.

I don't believe that it's fundamentally horribly dangerous; certainly
not as dangerous as, say, a splice outside a junction box or such like,
but it *is* against code. I believe that the reason for this particular
code is that there exists a possibility of inductive heating which
could, in a rare but not completely impossible circumstance, cause a
fire or other undesirable occurrance.

It's up to you what you want to do, but if it were I that was doing
this, if it wouldn't be too difficult I would try to run some Greenfield
between the wall box and the ceiling unit so that you could "do it
right." Not seeing your particular bathroom I have no idea if this
could be easily done with making only one or two holes or if it'd turn
into a near re-do.

nate

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

"Bill McKenzie" wrote in message
...
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.

It's gonna be real fun trying to squeeze a 10/2 into that tiny junction box.
The code requires all the circuit conductors be run in the same cable. You
have three devices, so you need neutral and three hot conductors, plus
ground. What you have isn't correct and hasn't ever been correct. At the
very least, you'll need to scrap the 10/2 and use a 12/3, plus the existing
12/2. You'll run three hots and two neutrals, plus grounds

On Jun 2, 8:12*pm, "RBM" wrote:
"Bill McKenzie" wrote in message

...
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.

It's gonna be real fun trying to squeeze a 10/2 into that tiny junction box.

N8N wrote:
12/2. You'll run three hots and two neutrals, plus grounds.

I'm curious if he really has 10/2; wouldn't that be unusual for a
bathroom which I would assume would be a 20A dedicated branch circuit
(hopefully GFCI protected?)

10/2 does sound odd.


Also, I *thought* but may be mistaken - someone correct me if I am -
that current code prohibited using two different size wires on a given
branch circuit, even if the smaller size used was appropriate for the
overcurrent protection device.

You can use any size wire as long as the overcurrent protection is for
the smallest branch circuit wire.

Mixing may or may not be a good idea. It can cause confusion. But on a
20A circuit you might run #10 to a garage for voltage drop and #12
within the garage.

--
bud--

On Jun 3, 10:20*am, bud-- wrote:
N8N wrote:
12/2. You'll run three hots and two neutrals, plus grounds.

I'm curious if he really has 10/2; wouldn't that be unusual for a
bathroom which I would assume would be a 20A dedicated branch circuit
(hopefully GFCI protected?)

10/2 does sound odd.



Also, I *thought* but may be mistaken - someone correct me if I am -
that current code prohibited using two different size wires on a given
branch circuit, even if the smaller size used was appropriate for the
overcurrent protection device.

You can use any size wire as long as the overcurrent protection is for
the smallest branch circuit wire.

Mixing may or may not be a good idea. It can cause confusion. But on a
20A circuit you might run #10 to a garage for voltage drop and #12
within the garage.

--
bud--

OK, I'm probably full of it there. It's probably 12/2 and 14/2, but
one is definitely bigger than the other. The big one has black outer
coating and the smaller one is white, but I doubt that means
anything. I'll crawl up in the attic tonight and see if I can read
the writing on the cable. In any case, I think i'm going to skip the
heater and just go with fan and light. Gotta figure out which of the
80-odd circuits it's using.

Supplemental question: Any problem with using expandable foam
insulation to seal the box around the hole in the drywall (top down,
from the attic)?

On Jun 3, 10:20*am, bud-- wrote:
N8N wrote:
12/2. You'll run three hots and two neutrals, plus grounds.

I'm curious if he really has 10/2; wouldn't that be unusual for a
bathroom which I would assume would be a 20A dedicated branch circuit
(hopefully GFCI protected?)

10/2 does sound odd.



Also, I *thought* but may be mistaken - someone correct me if I am -
that current code prohibited using two different size wires on a given
branch circuit, even if the smaller size used was appropriate for the
overcurrent protection device.

You can use any size wire as long as the overcurrent protection is for
the smallest branch circuit wire.

Mixing may or may not be a good idea. It can cause confusion. But on a
20A circuit you might run #10 to a garage for voltage drop and #12
within the garage.

--
bud--

One more thing. How can it be both dedicated and GFCI protected? Is
there a standalone interrupt/reset somewhere? There is a GFCI-
protected plug in the bathroom, but I'm assuming its a different
circuit. And I guess current code may not be relevant, since this was
all done in the 70s.

On Jun 3, 2:14*pm, Bill McKenzie wrote:
On Jun 3, 10:20*am, bud-- wrote:





N8N wrote:
12/2. You'll run three hots and two neutrals, plus grounds.

I'm curious if he really has 10/2; wouldn't that be unusual for a
bathroom which I would assume would be a 20A dedicated branch circuit
(hopefully GFCI protected?)

10/2 does sound odd.

Also, I *thought* but may be mistaken - someone correct me if I am -
that current code prohibited using two different size wires on a given
branch circuit, even if the smaller size used was appropriate for the
overcurrent protection device.

You can use any size wire as long as the overcurrent protection is for
the smallest branch circuit wire.

Mixing may or may not be a good idea. It can cause confusion. But on a
20A circuit you might run #10 to a garage for voltage drop and #12
within the garage.

--
bud--

One more thing. *How can it be both dedicated and GFCI protected? *Is
there a standalone interrupt/reset somewhere? *There is a GFCI-
protected plug in the bathroom, but I'm assuming its a different
circuit. *And I guess current code may not be relevant, since this was
all done in the 70s.- Hide quoted text -


There's an either/or in the code; if the GFCI outlet is on a 20A
circuit that is only used for bathrooms, the lights etc. can be on
another circuit. However if the fan is in the shower area it also
must be GFCI protected.

rather than crawl around the attic, why not just get some scraps of
12AWG and 14AWG and see if they match the sizes of the wires in the
box? I suspect you will find that the larger cable is 12AWG in which
case I would replace the 14/2 with a 12/3.

nate

"Bill McKenzie" wrote in message
...
On Jun 3, 10:20 am, bud-- wrote:
N8N wrote:
12/2. You'll run three hots and two neutrals, plus grounds.

I'm curious if he really has 10/2; wouldn't that be unusual for a
bathroom which I would assume would be a 20A dedicated branch circuit
(hopefully GFCI protected?)

10/2 does sound odd.



Also, I *thought* but may be mistaken - someone correct me if I am -
that current code prohibited using two different size wires on a given
branch circuit, even if the smaller size used was appropriate for the
overcurrent protection device.

You can use any size wire as long as the overcurrent protection is for
the smallest branch circuit wire.

Mixing may or may not be a good idea. It can cause confusion. But on a
20A circuit you might run #10 to a garage for voltage drop and #12
within the garage.

--
bud--

One more thing. How can it be both dedicated and GFCI protected? Is
there a standalone interrupt/reset somewhere? There is a GFCI-
protected plug in the bathroom, but I'm assuming its a different
circuit. And I guess current code may not be relevant, since this was
all done in the 70s.

It could be fed from a GFCI breaker, or the circuit can be broken through a
GFCI outlet, separate from the one by the sink, or protected by a faceless
GFCI mounted in a closet or other obscure location. Most likely, given when
it was installed, there is no GFCI protection on it, and none is required
unless it's installed over a tub or shower