Branch wire size for exhaust fan with lights and heat

[solarken]

Installing an exhaust fan on 20A ckt that requires 4 switches, for heat(14.1A), fan(.5A), light(.1A), and night light (negligible). Can I use the existing 12/3 for heat and fan, and run 14/3 for the 2 lights, all off the same 20A breaker, or do I need to use all #12?

 

[wwhitney]

That would violate 240.4(D) unless you install an additional 15A OCPD for the 14/3. For copper, use only #12 or larger on your 20A OCPD, unless in an application referenced in 240.4(G).

Cheers, Wayne

 

[LarryFine]

Installing an exhaust fan on 20A ckt that requires 4 switches, for heat(14.1A), fan(.5A), light(.1A), and night light (negligible). Can I use the existing 12/3 for heat and fan, and run 14/3 for the 2 lights, all off the same 20A breaker, or do I need to use all #12?

If it's all going to be on one 20a breaker, just run a single 12-2.

You don't need or want any more wires in the box than necessary.

 

[wwhitney]

If it's all going to be on one 20a breaker, just run a single 12-2.

That works if the unit has a single neutral connection, or if you are happy to tie the unit's multiple neutral connections together (no reason not to if it's all the same branch circuit, as far as I can see). Best practice is run the new 12/2 right on top of/next to the existing 12/3 everywhere, to approximate a single 12/5 cable. If there are any ferrous metal boxes involved, care must be taken; the simplest approach is bringing both cables through the same hole in the box.

This all assumes the unit does not require constant power, like most (all?) Panasonic units do.

Cheers, Wayne

 

[LarryFine]

I just realized that the OP means the wires between the switches and the fan/light/heater.

Yes, you need (at least) five wires. Yes, all of the wires must be #12, unless you add a 15a circuit.

 

[wwhitney]

Yes, you need five wires. Yes, all of the wires must be #12.

There are products on the market with automatic fan control that need more than five wires for the 4 functions. E.g. constant power (2 wires), contacts for manually turning on the fan (2 wires), and switched power for heat, light, and night light (3 more wires). [And possibly the heat has a separate neutral connection to allow you to power it from a separate circuit, so if you want to do that, you'd need 1 more wire. Not applicable to the OP.]

Cheers, Wayne

 

[solarken]

I just realized that the OP means the wires between the switches and the fan/light/heater. View attachment 2575399

Yes, you need (at least) five wires. Yes, all of the wires must be #12, unless you add a 15a circuit.

Thanks, that is what I was thinking, unfortunately.

 

[infinity]

I would run a single 1/2" FMC and pull in the wires needed.

 

[Little Bill]

I would run a single 1/2" FMC and pull in the wires needed.

Even with a plastic box?

 

[infinity]

Even with a plastic box?

Who said anything about a plastic box? But in answer to your question I would use metal box.

 

[Dennis Alwon]

I don't see why you couldn't use a plastic box as the flex would be grounded at the fan side assuming an equipment grounding conductor is run. Why not use LFNC?

 

[hillbilly1]

Smurf tube (ENT)

 

[Little Bill]

Who said anything about a plastic box? But in answer to your question I would use metal box.

The description of the fan and other equipment in the fan, especially the night light, just says residential, which is normally a plastic box.
Also, sounds like an install in an existing bath, not new construction.
No one mentioned the box, just what my thoughts are.