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Old 07-17-2010, 04:16 PM   #1
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Wire size to new bath heat/fan/light combo


New downstairs bath, installing a combo heat/fan/light unit in the ceiling. Have a dedicated 20A circuit with #12 wire coming to the switch junction box, a two gang metal box with a single gang reducer plate. Given the number of wires attached to the unit, and the limited space inside to cram all of them, I'd like to run two 14/3's to the unit from the switch. The instructions aren't clear, but I'm assuming that since everything in the unit is on a separate wire from the switch and the heater is fairly low wattage, that this won't be a problem. If the heater absolutely has to have a #12, how about using a #14 for the other functions? Seems physically impossible to cram six #12 wires plus grounds into the space available in the unit. Big enough problem trying to make all of those connections in a 2-1/2 inch deep box on the wall.

Thanks!

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Old 07-17-2010, 04:19 PM   #2
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Wire size to new bath heat/fan/light combo


yes, it will be a problem. Any wire on a 20 amp circuit must be at least #12.

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Old 07-17-2010, 07:15 PM   #3
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Wire size to new bath heat/fan/light combo


OK, but a follow-up question if I'm allowed:

The three switches that go in the junction box, actually a combo switch with two basic off/on switches for the heat and vent fan, and a three position switch for the light and nightlight, have pigtails to attach to the wires going up to the unit. The pigtail wires are all smaller than #14. What purpose is served by going back up to #12 from that switch up to the unit? Seems like at that point, we've broken the 20A/#12 rule already.
Thanks again.
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Old 07-17-2010, 07:33 PM   #4
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Wire size to new bath heat/fan/light combo


Quote:
Originally Posted by dsoelter View Post
OK, but a follow-up question if I'm allowed:

The three switches that go in the junction box, actually a combo switch with two basic off/on switches for the heat and vent fan, and a three position switch for the light and nightlight, have pigtails to attach to the wires going up to the unit. The pigtail wires are all smaller than #14. What purpose is served by going back up to #12 from that switch up to the unit? Seems like at that point, we've broken the 20A/#12 rule already.
Thanks again.
DFS
you can ask all the questions you want.

Quote:
Seems like at that point, we've broken the 20A/#12 rule already.
yes they have and glad you caught that. Now replace them with #12 like they are supposed to be.


One thing that might help you a little with space (and I hate doing this but I understand the dilemma)

the hot that comes into the box: do not pigtail that to the switches. leave it long enough so you can remove the insulation from the end and then back several inches from that. Then, loop the wire around the "line" side of the switches. This way you don't have any wirennuts for the feed in at least.

. If it works out right, the only wire nut you will have is one for the neutral and one for the ground wires. With the ground, you can do the loop thing to reduce the number of wires in the wirenut, hopefully to the point you can use a smaller wirenut.
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Old 07-17-2010, 07:55 PM   #5
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Wire size to new bath heat/fan/light combo


Pigtails, six of them, are hardwired into the switch, which is "hardglued" together.

Hot from line attaches to one of the pigtails, so your strip trick won't save any space :o(

Since the unit has a heater, fan and light, six wires plus grounds from the switch to the unit are called for - 2 times 12/3 makes for a lot of big wires ending in the small connection box in the unit. Again :o(
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Old 07-17-2010, 08:05 PM   #6
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Wire size to new bath heat/fan/light combo


You only need three hots a neutral and a ground. 4 wires not six.
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Old 07-17-2010, 08:17 PM   #7
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Wire size to new bath heat/fan/light combo


Hmmmmmmm....

Six connections plus two grounds at the unit:

night light - one black, heat - one red, two joined whites, second white to red striped white, fan - second red and finally the light - second black.

All of this supposed to fit into a box the size of a small cell phone.
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Old 07-17-2010, 08:20 PM   #8
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Wire size to new bath heat/fan/light combo


You should have a bigger box. If you are going to use the nightlight (I never do) you need 4 switches. It would be wise to use a countdown timer for the exhaust fan and a digital timer for the heat.
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Old 07-17-2010, 08:25 PM   #9
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Wire size to new bath heat/fan/light combo


Proby,
Switch is a combo, with a three position light switch to control the nightlight/light, and two single pole for the heat and fan - all in a single dacora size package. Box is a double gang, with a reducer to take the single size switch. Didn't want to mess with a timer on either the heat or fan. Like the simplicity of a single size switch to do it all. This is going into a seldom used guest bathroom.
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Old 07-17-2010, 08:27 PM   #10
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Wire size to new bath heat/fan/light combo


Quote:
=dsoelter;471096]Pigtails, six of them, are hardwired into the switch, which is "hardglued" together.
well not that is a dilemma.




Quote:
Since the unit has a heater, fan and light, six wires plus grounds from the switch to the unit are called for - 2 times 12/3 makes for a lot of big wires ending in the small connection box in the unit. Again :o
I do see your problem. Still doesn't allow you to downsize the wire. The switch is (or should be) listed to be able to have those wire sizes. I do understand your thought about they use smaller wires, why can't I. You can't because code says you can't.

Sounds like you need a different box. Either deeper or wider, or both. Sorry.
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Old 07-17-2010, 09:19 PM   #11
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Wire size to new bath heat/fan/light combo


I run ENT or smurf tube with individual conductors up to the unit from the switch box. This way i can take up my 3 hots, 1 neutral and 1 ground. I also don't use 2 1/2" boxes.
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Old 07-17-2010, 09:42 PM   #12
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Wire size to new bath heat/fan/light combo


Is it similar to this Broan unit

http://www.broan.com/ImageLibrary/br...s/99043764.pdf
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Old 07-17-2010, 10:01 PM   #13
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Wire size to new bath heat/fan/light combo


Yes, that's the one, Nutone version. Using with a Broan switch 77DV or DW, four function.

Nightlight was a plus, since it can light a dark bathroom for guests who stumble out of bed in search of the bath in the middle of the night.
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Old 07-17-2010, 10:45 PM   #14
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Wire size to new bath heat/fan/light combo


The branch circuit conductors must be #12. There is nothing wrong with the size of the factory pigtails on the combo switch. The circuit must be protected by a 20 amp breaker so that calls for #12 wire.

If you use Jims suggestion you can reduce the conductors at the ceiling unit by one neutral (white) and one ground so you will have 6 wires entering the fan unit instead of 8 all #12. Meaning you will only run one neutral #12 to the ceiling unit, one #12 ground and 4 #12 hots.

You can also do it the way the diagram shows but you cannot use 14/3 because the branch circuit must be 20 amps.

I might be mistaken but another way would be a 15 amp multiwire branch circuit using 14/3 to the switch box and two 14/3's to the bathroom unit. I don't think there would be an issue in doing that. Just a slight change at the switch ... the two pigtails from the switch that connect to the incoming hot in the factory diagram would each connect to one of the 2 hots of the multiwire 14/3 from the panel..
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Last edited by Stubbie; 07-17-2010 at 10:48 PM.
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Old 07-17-2010, 10:55 PM   #15
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Wire size to new bath heat/fan/light combo


Most of the fans with heaters in them require 20A.

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