Using a multiwire branch circuit to power a 240 V outdoor sauna and its lighting's 120 V power supply

[dbwest]

I am installing a barrel sauna in my backyard. Its 8 kW heater takes 240 V and is to be hardwired. The sauna also comes with an LED strip and an associated power supply, which takes 120 V and draws 0.35 A. The power supply has a male plug at the end of a flexible cord, but the sauna installation manual suggests that the power supply could be hardwired (the wires are 20 AWG). I have an installation in mind, but my electrical apprentice brain worries that there could be code violations.

I would like to install a two-pole 40 A breaker in my basement panel, from which I would pull two #8s to a disconnect on the side of my house. I would pull #10 ground to the disco. I would pull two #8s from the disco to the sauna, as well as the #10 ground and a #12 white from the panel. At the sauna, I would tap into one of the #8s with a #12 conductor leading to a 1 A in-line fuse, which would splice to the line side of the power supply's cord. I would splice the load side of the power supply cord to the #12 white. This arrangement affords me a few things: 1) only one multiwire branch circuit makes its way to the the sauna, so I wouldn't have to ground the structure per 250.32(A) exception; 2) I can take advantage of 240.5(A)/240.10 in that the flexible cord can get protected by a supplementary OCPD. I'm also bearing in mind 210.19(A)(4) exception #2, I think.

I was worried about the implications of 400.12(1) with respect to the flexible cord being hardwired, but the sauna's installation manual gives it as a suggestion, so I figured it is OK. My main concern now is GFCI protection. The heater explicitly says that it is not to be GFCI protected, but I wonder if the power supply in my proposed circuit would require GFCI protection given that the box from which the cord emerges would be outside. I would like to mount a box on the back of the sauna from which sealtite would emerge to carry the 240 V to the heater; the power supply's cord would also emerge from this box via a weatherproof cord grip.

 

[winnie]

1) The minimum size for circuit conductors is the required EGC size. So at a minimum your neutral would be a #10.

2) While this isn't a swimming pool or a hot tub, my experience in a barrel sauna suggests that there is lots of moisture and minimal clothing involved. In my own home for my own safety I would apply the same grounding and bonding rules applied to a hot tub.

3) Beware of any appliance manufacturer who prohibits the use of GFCI protection. This means that they have an unsolved current leakage issue. Do you really want to be wet and barefoot next to a heater that trips a GFCI?

(In the case of some types of heating element this might only be during the first use (or the first seasonal use) when moisture is being baked out.)

Jon

 

[retirede]

1) The minimum size for circuit conductors is the required EGC size. So at a minimum your neutral would be a #10.

2) While this isn't a swimming pool or a hot tub, my experience in a barrel sauna suggests that there is lots of moisture and minimal clothing involved. In my own home for my own safety I would apply the same grounding and bonding rules applied to a hot tub.

3) Beware of any appliance manufacturer who prohibits the use of GFCI protection. This means that they have an unsolved current leakage issue. Do you really want to be wet and barefoot next to a heater that trips a GFCI?

(In the case of some types of heating element this might only be during the first use (or the first seasonal use) when moisture is being baked out.)

Jon

A sauna is not necessarily wet. Some are capable of steam generation, but not all. Many infrared saunas are strictly dry.

 

[LarryFine]

Welcome to the forum.

I actually prefer having the convenience and control of having a sub-panel near the sauna.

I envision running a 50- or 60-amp non-GFCI'ed feeder, a six-space panel, an electrode, etc.

Put the GFCI protection there, a receptacle or two, and room for additions like area lighting.

 

[suemarkp]

If you can run a new cable to the sauna, you can just as easily run two. Bring both circuits up to a pole, one 40A double pole and one 15A single pole with a gfci receptacle or blank face gfci. Or run a feeder and put a small panel out there with two circuits and the ground electrode system.

Even though you understand how this should work and have a fuse for the small 120V tap, Im not so sure it is a legal tap and being a dwelling some future owner may not understand what is there. Keep it simple and normal. Running a separate 120V gfci circuit will allow other things to be plugged in to that circuit, like a radio or phone charger, or lawn mower, or ...