Bath fan wiring question

[dgman]

I am wiring a bathroom fan to a 20 amp circuit.  The incoming wires are 12 gauge but the fan wires are much smaller (14 or 16 guage)  .  Is there are problem with the smaller wires being connectedfd to the 12 guage wire on the 20 amp circuit?

Thanks

[Roly]

I am wiring a bathroom fan to a 20 amp circuit.  The incoming wires are 12 gauge but the fan wires are much smaller (14 or 16 guage)  .  Is there are problem with the smaller wires being connectedfd to the 12 guage wire on the 20 amp circuit?

Thanks

No.   Think of plugging in a table lamp or clock, those are 16 or 18 ga. .     All of your lighting fixtures will be way smaller than 14 or 12 gauge house.    Make sure the connections are secure by pulling on the wires after they are connected, sometimes going between the 12 and 16 ga. is problematic. Roly

[Don_M]

Practically speaking there should not be a problem. The only issue would be if the fixture would normally draw more current then the circuit was designed for (not likely with a bathroom light; even if it had a vent fan). I believe there is an NEC limitation on the length of 18AWG fixture wire that can be connected to a 12AWG branch circuit. but it is many, many feet (something like 50 feet). Basically the NEC assumes the fixture wire is designed to carry the load of the fixture itself. It doesn't really care if the fixture “burns up” – the Code is more concerned that the branch circuit is properly sized with the proper over-current protection.

[TDKPE]

What Roly said. The leads are part of a listed (UL, CSA) assembly, and as such, they were tested to handle a short circuit or ground fault long enough to trip the breaker and clear the fault. And carry the design full-load current of the unit continuously, of course. Like a table lamp can.

[photobug]

What Roly said.  The leads are part of a listed (UL, CSA) assembly, and as such, they were tested to handle a short circuit or ground fault long enough to trip the breaker and clear the fault.  And carry the design full-load current of the unit continuously, of course.  Like a table lamp can.

Interesting take on the upped capacity of the smaller wires.

No scientific or factual basis but I always assumed the wires were all contained in a metal box/container.  So when the 20 gauge wires were attached to the 12 gauge wires, if there was a fault the fire would stay contained within the fixture.  But then there would be a contained fire instead of a blown circuit.

[TDKPE]

Interesting take on the upped capacity of the smaller wires.

No scientific or factual basis but I always assumed the wires were all contained in a metal box/container.  So when the 20 gauge wires were attached to the 12 gauge wires, if there was a fault the fire would stay contained within the fixture.  But then there would be a contained fire instead of a blown circuit.

18 gauge copper with 90C insulation is good to 14A continuous (per the NEC), though that's not allowed in fixed building wiring, which starts at 14 gauge (which in turn is actually good to 25A continuous with 90C insulation*).  But it is allowed in listed utilization equipment.  And it can carry enough current in short lengths (hundreds of amperes for half a cycle or so) to trip even a 20A breaker in a direct short or ground fault.  It'll probably torch the wire, like it can blow a small divot out of a screw driver, but it should trip the breaker in the process.

And whether it does or doesn't, it's good that it's in a box or conduit.   


*but is held to 15A max by an obelisk note at the bottom of the table.  Derating, though, is based on the tabulated ampacity based on insulation, which is 90C for NM (Romex).

[LeeThoms]

Haven't you consulted a professional to get this done easily.

[Robert Adams]

I am wiring a bathroom fan to a 20 amp circuit.  The incoming wires are 12 gauge but the fan wires are much smaller (14 or 16 guage)  .  Is there are problem with the smaller wires being connectedfd to the 12 guage wire on the 20 amp circuit?

Thanks

No, no problem at all that's normal. You could run a circuit with 8 ga wire and all is good. It's when the demand of the installed fixture needs more than the circuit can handle it's an issue.

   The wires in your house are sized for their length and their amp capacity. So longer runs will have bigger wires than would be needed for a very short run. Simplified answer but gets the point across. Like having a 6 lane freeway and only using one lane of it.