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Got a Siemens 60-amp switch (LNFC222R) that's for a pottery kiln. One side of the switch will have a #6 Cu NMD90 wired to it and will go to the sub-panel, running through studs, just like the 14-2 wire in the picture. The other side of the switch will be wired to the kiln.

It's in a shed. There are currently no walls and the studs are exposed.

Question:

How do I mount the switch? Supposing I want to pass an inspection, do I need to cover the wall? If I mounted the switch over a wall covering, how would the #6 Cu wire pass through the box and into the wall? Does it need protection? There is a knock out in the back of the box, but supposing I put up drywall and mount the box on top of it, I can't run the wire through the drywall because it's a combustible.

If I mount the switch between the studs, fine. Easy peasy. But say I want to finish the shed and put up drywall or cement board. I could cut a hole that the switch fits through, but the box doesn't seem to be designed to be inset (so to speak) into the wall, given the way the cover opens.

Pictures show where we want to put it.

Thanks for the help.

Danny enter image description here enter image description here

Danny
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  • Yeah, enclosed safety switches like that aren't designed to be flush-mounted at all. And are you saying that the wire's a combustible, or that the drywall is?! – ThreePhaseEel Mar 26 '20 at 04:12
  • @ThreePhaseEel yes, I'm saying drywall is combustible. Am I wrong? Can you run wires through drywall? Maybe with a jacket? I have no idea what the 'rules' are.. – Danny Mar 26 '20 at 05:10
  • I have to admit I've never thought of disposing of drywall by tossing it in the wood stove... – Harper - Reinstate Monica Mar 26 '20 at 05:48
  • It's common to put up a square of plywood and then mount the switch to breaker panel to that board, but I'm not sure if that's what you're asking... – JPhi1618 Mar 26 '20 at 14:09
  • @Danny -- also, have you considered taking that switch back and getting one that's in an enclosure designed for indoor use? (the one you have is in a NEMA 3R, outdoor rated box, which limits your flexibility unless you wish to field punch knockouts) – ThreePhaseEel Mar 26 '20 at 23:00
  • No I hadn't considered that, and I was also unaware of that. What do you mean by 'field punch'? Thanks! – Danny Mar 26 '20 at 23:34
  • @ThreePhaseEel we followed the manufacturer's recommendation to put a 60 A circuit on a kiln that's rated 48.5 peak amperage. We did that to avoid 'nuisance tripping'. We didn't realize the kiln comes with a 50 A plug. Using a switch / junction box is the solution because a 60 A plug / receptacle is more expensive and complicated. – Danny Mar 26 '20 at 23:59
  • @ThreePhaseEel I'm looking around on line and can't find a junction box or switch that's appropriate or specified for indoor application. I'm guessing this is why I'm banging my head against the wall in so far as particulars of the wiring installation, i.e. how to run the wires inside the wall when the knock outs on the switch are outside.. – Danny Mar 27 '20 at 00:01
  • @Danny -- try looking in Siemens' General Duty switch line if you want a better selection of enclosure types; note that for non-fusible switches, they only make 3-pole versions, as you're expected to just use the outer two poles in a two-pole application – ThreePhaseEel Mar 27 '20 at 01:26
  • @ThreePhaseEel so a Siemens GNF322 would do the trick? Kinda hurts - they're triple the price of the LNFC222R. Any idea if I can get away with using the latter, even though it's outdoor rated? Like I said, there is a knock out in the back of it, so I can run the NMD90 #6 Cu to the sub-panel. Still have no idea how to run the kiln wire to the box... – Danny Mar 27 '20 at 04:49
  • @Danny -- it's possible to make your own knockouts in electrical boxes (usually metal ones) using a *knockout punch set* (in fact, some larger boxes don't come with knockout points from the factory, expecting the installer to make their own). And yes, you can get away with the latter, it's just a bit more awkward to do so – ThreePhaseEel Mar 28 '20 at 00:10
  • @ThreePhaseEel Right on. Anything to know about the kiln wire running up the box? As long as it's secured? – Danny Mar 28 '20 at 01:00
  • @Danny personally, the idea of a local disconnect for the kiln is a good one, but I'd use a receptacle anyway. NEMA 14-60 isn't *that* terribly rare/expensive of a plug/receptacle type (although it's not quite the *right* one for this application) – ThreePhaseEel Mar 28 '20 at 01:23
  • Why would you use a receptacle? Do non fused switches have potential to fail? – Danny Mar 28 '20 at 01:33
  • @Danny -- more to provide a clean transition from the kiln's cord to the shop wiring (and so you don't have to take stuff apart if the kiln needs to travel) – ThreePhaseEel Mar 28 '20 at 01:41
  • Gotcha. Thanks for all the help. Good to know all this stuff. – Danny Mar 28 '20 at 04:41

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Those switches are designed for surface mount, the operator or handle needs to be open. In the US that Romex will need to be covered below 8’ not just the kiln but the existing wire to the light switch. Code allows for 1/2” sheetrock or plywood to protect the cables in the walls. I would use plywood to mount the switch especially if you will be regularly cycling the switch.

The knockout in the back of the box can be used but you will want at least a 3/4” clamp I usually use 1” clamps with #6 4 wire cables because 3/4” is really tight and some brands do not fit 3/4”. The clamp secures the wires and protects the insulation from the sharp edges of the knockout hole.

Ed Beal
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  • Great! I'll mount with plywood and use the knock in the back of the box for the Romex cable. There's only one knock out in the rear plate of the box. How should I run the cable coming from the kiln? Gotta use the knock out on the side or bottom of the box. Seems like you're saying the kiln cable needs to pass into the wall and back out? – Danny Mar 26 '20 at 19:10
  • To be clear, the plywood will have to go from the floor to at least 8ft (or the top of the wall) to make that compliant. The conductors from the kiln would need to be in conduit, flex conduit is allowable, but you can't just run wires alone. Alternatively if you had just bought a 60A receptacle and a matching plug for the end of some portable cord for the kiln, you would not have needed the disconnect switch. That is still an option though. Look for what's commonly called a "welding connector". – JRaef Mar 26 '20 at 23:00
  • Yes, I understand the plywood has to cover the whole wall for it to be spec. What do you mean 'run the wires alone'? 60 A plug / receptacle is way more expensive. Not sure why you mentioned a welding connector. Wire from kiln has to get to the switch somehow, whether that's outside the wall or inside the wall. I assume it should run along the floor and to the wall. – Danny Mar 26 '20 at 23:33
  • From there, I'm not sure if the kiln cord should run inside the wall, up to the switch, then pass through the wall again to the outside where there's a knock out available on the switch, or if it should just run the kiln cord along the outside of the wall to the switch. – Danny Mar 26 '20 at 23:33