Installing A Pottery Kiln

johnliu_gwNovember 10, 2011

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. I'll put a smoke detector in the garage, and possibly a fan to vent fumes.

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. We'll run the kiln at night. 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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normel

The kiln will run for more than 3 hours, so the wiring and breaker need to be sized at 1.25 times the rating on the name plate. If you have the extension, you will need 6ga Cu and a 50A breaker. No need for a GFCI.

    Bookmark   November 10, 2011 at 2:09PM
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johnliu_gw

Thank you. I'll do that.

    Bookmark   November 10, 2011 at 6:49PM
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petey_racer

Do NOT GFI this circuit if you value your marriage.

    Bookmark   November 10, 2011 at 8:39PM
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johnliu_gw

How come? Will it tend to shut off the kiln in mid-fire or something?

    Bookmark   November 10, 2011 at 10:55PM
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brickeyee

"Will it tend to shut off the kiln in mid-fire or something?"

It can and GFCI protection is not required on 240 V circuits.

    Bookmark   November 11, 2011 at 10:23AM
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lbpod

Your electric bill, after the installation of the kiln,
will cause you to ponder the necessity of the kiln.
(just guessin)

    Bookmark   November 11, 2011 at 2:48PM
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johnliu_gw

Should cost about $9 per firing, I think. About $0.11/kwh here.

    Bookmark   November 11, 2011 at 6:13PM
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johnliu_gw

Should cost about $9 per firing, I think. About $0.11/kwh here.

    Bookmark   November 11, 2011 at 7:36PM
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alphonse

"...and possibly a fan to vent fumes."

I'd consider this a must unless you leave the garage door open.
Bisque firing isn't too bad but glazes seem toxic, even if they aren't.

    Bookmark   November 12, 2011 at 5:04AM
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johnliu_gw

Circuit done. Thanks! I did mess up initially by using 1/2" conduit, had to re-do it with 3/4". #6 conductors, 50A breaker.

Two things left to do.

#1 is a vent. There is a downdraft vent specifically made for the kiln, connects to the bottom and pulls out contaminated air before it ever gets into the room, but it costs $500. So, unless I can devise a homemade version of that, I'll put a vent in the garage wall and call it good.

#2 is some sort of heat shielding on the nearest wall. The kiln will be on a mobile base, so that it can be pulled away from the wall when firing and then pushed against the wall to be out of the way. But suppose it gets turned on without being pulled away from the wall? I'm thinking of mounting a steel sheet on stand-offs, with 6" clearance from the wall. I need to go see what people do for this situation.

    Bookmark   November 13, 2011 at 9:47AM
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brickeyee

"I'm thinking of mounting a steel sheet on stand-offs, with 6" clearance from the wall."

A layer (or two) of cement board (tile baker) would be better.

It does not conduct heat well at all, unlike metal and metal standoffs.

If you use metal two layers with an air space between them are required to create a decent barrier.

    Bookmark   November 13, 2011 at 10:04AM
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