Am I using 12/3 cable from a switch to an outlet correctly?

[Leadbenny]

I'm installing a hardwired towel warmer and I thought I would include an outlet on the same cable because the towel warmer needs a junction box anyway. Can I run a 12/3 with both black/red hot, black attached to the switch, to the outlet connected to red, and continue the black to the towel warmer with all neutrals and grounds connected? It's 20 amp protected by a GFCI outlet upstream. See diagram for clarity:

EDIT: the circuit is connected to a GFCI outlet upstream of the switch

 

[wwhitney]

The way you've drawn the diagram is correct. I would think it would be more typical to use red for the "switched hot" and black for the "constant hot", to match the colors in a typical 12/2 feed. But it doesn't matter.

Note that the outlet box and the switch box will each need to have a volume of at least 8 * 2.25 = 18 in^3.

Cheers, Wayne

 

[Sponsor]

 

[Leadbenny]

Thanks for info.

Oof on the box size. I don't think I can even get a 3 1/2 inch deep box where I am.... I'm only finding 3"..... Also, going off the calculations here my outlet box has 10 "wires" (2 black, 2 white, 1 ground, 1 red, 2 for device, 2 for clamps). I'm prepared to get a 3 inch box, but I don't think I can really do anything else beyond that.....

 

[Afjes]

I would do a bit more research first before you install a regular receptacle. You may have to rethink this but consider the towel warmer is metal, if for any reason the body becomes electrified you now have this energized large piece of metal in a small room with a lot of water and dampness which will accumulate on the towel warmer. I would highly consider putting a gFCI prior to the towel warmer to protect persons from electrocution.

Are you sure the towel warmer does not include with its installation instructions to use GFCI protection. Since you will be usin a MWBC you may want to consider using a 2 pole GFCI breaker if you can.

 

[wwhitney]

2 for clamps

I'm of the opinion that the clamp allowance only applies to a box like the one below, which is a standard metal box (standard volume per the NEC table) that has internal metal clamps. The molded plastic boxes with clamps cast into them, the listed volume already includes the effect of the clamp.

RACO 4 in. W x 1-1/2 in. D 2-Gang Welded Square Box with Three 1/2 in. KO's and 1 TKO, NMSC Clamps, FS Bracket, Flush, 1-Pack 223 - The Home Depot

Manufactured from durable pre-galvanized steel. Designed to house and protect electrical wiring, switches, and receptacles. UL Listed and acceptable for use in 2-hour fire rated walls. Device mounting

www.homedepot.com

Edit: I see now you're in Canada, so I'm not familiar with whether the rules for the CEC are different.

Cheers, Wayne

 

[Leadbenny]

I would do a bit more research first before you install a regular receptacle. You may have to rethink this but consider the towel warmer is metal, if for any reason the body becomes electrified you now have this energized large piece of metal in a small room with a lot of water and dampness which will accumulate on the towel warmer. I would highly consider putting a gFCI prior to the towel warmer to protect persons from electrocution.

Are you sure the towel warmer does not include with its installation instructions to use GFCI protection. Since you will be usin a MWBC you may want to consider using a 2 pole GFCI breaker if you can.

Thanks for your concern. Yes the instructions to say to have a gfci protected circuit. The circuit will be GFCI protected upstream via a 20 amp gfci outlet before entering the switch box.

 

[Leadbenny]

I'm of the opinion that the clamp allowance only applies to a box like the one below, which is a standard metal box (standard volume per the NEC table) that has internal metal clamps. The molded plastic boxes with clamps cast into them, the listed volume already includes the effect of the clamp.

RACO 4 in. W x 1-1/2 in. D 2-Gang Welded Square Box with Three 1/2 in. KO's and 1 TKO, NMSC Clamps, FS Bracket, Flush, 1-Pack 223 - The Home Depot

Manufactured from durable pre-galvanized steel. Designed to house and protect electrical wiring, switches, and receptacles. UL Listed and acceptable for use in 2-hour fire rated walls. Device mounting

www.homedepot.com

Edit: I see now you're in Canada, so I'm not familiar with whether the rules for the CEC are different.

Cheers, Wayne

The internal clamps sit basically flush within the box.....I'm not totally sure how they're factored in calculations in Canada, but I'm going with a 3" box.

 

[Fitter30]

Why switch the outlet? Still run a shaver not hair drier. Towel bar will take more than a few minutes to heat up a towel. Make sure gfi is rated for 20 amps.
2000watts/ 120/volts = 17 amps

 

[Afjes]

Fitter30
The outlet (receptacle) is not being switched. It has a constant hot from the MWBC power in which is in this diagram the red wire.
Power in feeds the switch and the receptacle at the same time.

 

[wwhitney]

Since you will be usin a MWBC you may want to consider using a 2 pole GFCI breaker if you can.

The OP doesn't show an MWBC, it's just a supply with both constant power and switched power, in phase with each other.

Cheers, Wayne

 

[Afjes]

The OP doesn't show an MWBC, it's just a supply with both constant power and switched power, in phase with each other.

Right you are!!

My eyes never went down to supply line to see x/2. my mind just said x/3