Electrical Question
 

Electrical question. Wifey wants her pottery kiln set up. I plan to do it in the garage, where I previously installed a 100A subpanel with a 60A main breaker, powered by a 60A breaker on my main panel and a ground cable to ground rods. The kiln will have the appropriate clearances to combustible surfaces.

Here is a picture of the information plate. The plug is a NEMA 6-50 with two flat (hot?) prongs and a round (ground?) prong.

As I interpret this, I simply need to install a 40A 240V circuit breaker in my subpanel, and the appropriate wall receptacle, wired to the hot terminals of the breaker and the ground bar in the subpanel, via conduit. The receptacle will be dedicated to this use. I will try to find a GFCI breaker. Am I missing anything?

The plate says

"2 way 240v AC
1 phase 21.7 amps
5200 watts
With . . . extension ring
32.5 amps 7800 watts"

I think we have the extension ring, but will check.

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It sounds OK to me. It is a 32.5 A 240V resistive heating load. You need a 40A double pole breaker - you only need a GFCI if it is a wet environment. Wet clay maybe?

Disclaimer: I am not an electrician & you should confirm with your local authority.

Ian

Yes. You don't need a GFCI receptacle (unless it is code) and I doublt you could find one.

You can use a twist lock receptacle or a 'dryer' style.

It is not a wet garage. I used GFCI receptacles for all the 120 V outlets anyway, since I figured they could someday be used to run some portable thing that might get wet. The 240 V, 20 A circuit that runs my table saw is not GFCI, as I'm never going to pull that thing outdoors to use. For the kiln, it will always stay inside the garage. I know I cannot find a GFCI receptacle for this, but I could possibly find a GFCI breaker if need be.

I wouldn't bother with the GFCI. If the kiln has no timer or other device requiring 120v, then the 3 wires go as you stated, one hot on each phase through a double pull breaker and the ground wire to the ground buss.

However, the new panel should be tied to the main with an isolated ground.

Please read this for a complete explanation of how a sub panel is to be installed:
Definition of Subpanel Ground/Neutral Isolation [Archive] - The Garage Journal Board

220, 221, whatever it takes.

The easiest way to wire it is to skip the plug - unless you intend to move it around. Wire with 2 x #8 wire + ground (maybe a solid #10???) in the conduit to a 72171C junction box. From there to the kiln use a flexible shielded BX cable. Or just flex sheathing with more #8.

I would be tempted to just buy 8/3 BX (shielded range cable so it should be widely available) & just not use the neutral (white).

Ian

If he uses 10 gauge wire and a 40 amp breaker into a 6-50R he will be able to plug his welder into it.:)

I want the plug, so that we can move the kiln out if I need the space for another project. I have some leftover #6 conductors and #8 bare ground (I think) from wiring the sub panel, so I'll use that. I've been told that, as the kiln will operate for over 3 hours, I need to up-rate everything to 1.25X the spec on the plate, so a 50A breaker. I guess I won't be wanting to run my saw when the kiln is going . . .

I doubt that will be an issue.

You won't be running your saw ever again.

Do you not realize that she is taking over your space? Forever.

Well, she did spend three weekends cleaning and organizing my garage so that I'd have a nice place to make stuff for her, I think that deserves some credit. Now if she'd just iron my shirts.

We've set up her pottery studio in the basement. Slab roller, wheel, handbuilding table, storage, etc. We were going to put the kiln down there, but for safety, venting, and electrical reasons I decided to put it in the garage.

A project for later is to build me a darkroom in the basement.

I agree, no plug. Hard wire to a J-box.

That's an interesting project. Darkroom gear should be *really* cheap right now, except for chemicals. I bought a batch of film chemicals a few months ago and was astounded that the prices have basically doubled over the last few years.

Dan

Done. Thanks all. Actually I did it twice. In between, I realized that the wire fill was too much for the conduit size initially used.

Now I need to pick up a mobile base for her kiln. Also I think I'll mount a sheet steel panel too the wall nearest the kiln, with a 6" airspace between panel and wall. The manufacturer's specs say 18" between kiln and a combustible wall, I think I'll feel better with 18" between kiln and non-combustible panel, then 6" to the wall.

If you do skip the plug (doesn't sound like it, but...) you'll still want some kind of disconnect at the kiln.

If you get to the point where you're ready for the darkroom, I have an enlarger that I'd part with cheap.

Thank you. I have a Beseler 23C in storage. I'd like to find a Beseler 45 enlarger.

The main issue with the darkroom will be the sink and plumbing. I have never done plumbing, beyond tightening a P trap. The laundry sink is 6 feet away, so easy enough to route supply and drain lines. I would need to learn how to braze (?) copper pipe. Cutting and gluing PVC drain line I can manage :-)

The sink will have to be custom, to fit in the space. I could make it from wood then fiberglass or otherwise coat it. Or I could get one made from stainless steel.

Thanks Zeke/milt. Yes, the subpanel ground is not bonded, is connected to the main panel's ground, and is also connected to two 8' ground rods outside the garage.

Sweating copper pipe is a piece of cake. There's fittings out now that already have solder inside them that are a snap to use that I've used a couple times, they've held up for me. If you use the traditional dry fit, cut the pipe to length, prep the ends (buff them up with emory cloth and coat with flux), slip the fittings on, heat until it blows slightly green flame, place the tip of the soldering wire against the joint, it will melt and suck the solder in. When you see the first drip, you're done. Wipe the excess solder off carefully.

Try it a couple times on some scrap, you'd be surprised how easy it is to do. Just dont forget a piece is hot and grab it my mistake. BTDT.

It is not as easy as it once was. The removal of lead from the mix has made it more difficult.