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Electrical Wiring

bathroom fan light wiring size

15 years ago

I have a dedicated 20 amp line 12/2 to power a bath GFCI recip and a fan/light combo. Wiring the fan/light after the GFCI, can I run 14/3 to the fan light or switch? I have a piece of 12/3 to make one of the runs but am otherwise out of 12/3. So can the line back to the switch be 14/3? Or can I run two pieces of 12/2 back to the light switch? Please help me not buy more cable and be legal too.

Featured Answer

Ron Natalie

15 years ago

The NEC allows the other outlets (light, fan) to share the 20A receptacle circuit as long as that circuit serves only outlets in that one bathroom.

Multiple bathrooms can be served from the same circuit if only receptacles are on the circuit.

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Comments (9)

lonesparky95
15 years ago
You're not allowed to use #14 AWG anywhere on a 20-amp ckt, not even for pigtails.

As for the rest, I can't imagine why you'd want the fan/light combo on the load side of a GFCI. Nothing to be be gained but nuisance. I'd pigtail that connection on the line side of rcp.
billhart
15 years ago
It is probably easier for an amateur to pack everything in the box if they use the LOAD side instead of adding pigtails in the box.
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(1) is the source of power, as you surmised and determined empirically. One of the cables goes to another room and the switch does not affect it. The black from that cable is paired with the black of the cable from the power source and a pigtail from that junction goes to the switch to power it. The other two blacks are one for the fan and one for the light. Since there is just one circuit, the whites can be left spliced together. The blacks for the light and fan each need to be controlled by separate switches. A 2-gang box must be installed instead of the single gang you now have. The existing single gang must be really crowded. It probably exceeds box fill specifications.
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You're free to run the fan from a general lighting circuit. Barring one of the units that has a heater integral to it, it ought not to cause a load issue. Once you've tapped into the other lighting circuit, you can either use a switch leg or just run a feed down to the switch box (in addition to running to the fan). The only issue you need to check is if the fan instructions requires a GFCI (normally only if they're installed within the shower area). If so, you'll need to find a way to protect it appropriately.
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What you have is one cable bringing in power and the other cable goes to the switch (a switch loop). By wiring the black from the switch to the black from the power (and the same for the whites), you created a dead short from hot to neutral when you turned the switch ON. This was NOT the the way you originally found it. You probably welded the contacts in the switch together when you turned it on, necessitating its replacement. Turn off the bathroom breaker to be able to reset the main. The way it should be wired, for both lights and the fan to be operated by the switch is: Black from the power cable connected to the white from the switch leg. Black from the switch leg connected to the blacks from the lights and fan. Whites from the lights and fan connected to the white from the power cable. All green and bare copper ground wires connected to each other.
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Comments (6)
I couldn't pull up your wiring diagram.I replaced my bathroom exaust fan some years back.I had a GFCI that fed a double-single pole switch which powered my fan and a 5 bank of vanity lights.The new exaust fan had 1-60watt light and a 25-watt night light.To run it I had to add another double-single pole switch.In order to wire it to the switch I had to wire a WHITE(NEUTRAL)as a HOT BLACK WIRE. It's very rare to have to do this but in my situation the CODE allowed it.That means connecting a black(hot) to a (nuetral) white.The original fan was fed from a GFCI.So in order to connect my 2 double-single pole switch's I had to use a WHITE (NEUTRAL) AS A HOT WIRE.I also marked it with a marker and coiled some electrical tape around it to have no doubt that was a live hot wire.I would suggest you contact an electrician if you don't understand the wiring diagram or are unsure how to make the connections.Its always worth the extra money to keep your family safe.When in doubt call an electrician.
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av8r
15 years ago
Or to use the extra set of slots on the line side and not pig tails....
tombijak
15 years ago
Fan/lights "over the bath/shower" are allowed per mfgrs. UL listing which always requires the circuit to be GFI protected. I typically install a separate lighting circuit for this type application w/ GFI breaker in the panel. I guess the NEC allows the lights in the bath to be on same circuit as the required 20AMP GFI receptacle, but you'd have to check if the fan/light allows for 20AMP overload protection or the more likely 15AMP.
tombijak
15 years ago
Agreed that the NEC allows light/fan in same bathroom to share the 20A receptacle circuit, but you have to also confirm that the particular light/fan you're installing is OK w/ the higher 20Amp overload protection.
lonewolf20
15 years ago
looking at old threads trying to gain knowledge. I have on observation to make.It would seem most questions are asked by do it yourselfers that have a basic knowledge at best and yet the answers seem to be between electricians who should allready know the answer.can we please try to simplify the answers? now my question about the pry answer. what doees the mean/ if ok with 20amp overload pretection?
davidandkasie
15 years ago
now my question about the pry answer. what doees the mean/ if ok with 20amp overload pretection?

it means if the manufacturer of the light says to protect it with a maximum 15A OCPD, then you cannot put it on a 20A circuit.

as far as simplifying answers, they have been dumbed down drastically already. if you cannot understand a particular response, ask for clarification. if you still cannot understand, then it is best to let a pro handle the job. fooling with electricity is not for everyone, no shame in that.
lonewolf20
15 years ago
another dumb diy question, if code calls for 20a service why would a manu. make a 15 amp fan, light?

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