I bought my wife a smallish Kiln and it requires a 20 amp circuit.

Right next to where we want to use this Kiln is our hot water tank which is on a dedicated 30 amp circuit coming out of the main breaker box.

I want to run a 12 AWG wire out of the disconnect box for the hot water heater down the wall about 3 feet then connect a 20 amp GFCI outlet to plug this Kiln into.

1) Is this ok to do?

2) If yes, should I also install a single 20 amp breaker between the disconnect box and the outlet?

3) If yes to the single 20 amp breaker, is there a specific small single breaker box I can use?

  • That's what I was afraid I would be told. :( Thanks for the super quick reply! – Dave Feb 1 '19 at 16:29
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    You got your answer, but just to clear something up - the breaker is sized to protect the wire connected to it. Don't think of it matching the appliance, think of it as matching the size of the wire you're using. So, in your scenario, 12AWG wire would need to be protected by a 20A breaker. A 30A would not protect the smaller 12awg wire. – JPhi1618 Feb 1 '19 at 16:39
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    Is this "smallish" kiln 240 V or 120 V? – Jim Stewart Feb 1 '19 at 23:33
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    Is there a reason you can't run a new circuit from the breaker box? – ThreePhaseEel Feb 1 '19 at 23:54

No. Your water heater is on a 30A circuit because that's (presumably--unless it's extraordinarily small) what it requires. There's no overhead in the circuit for additional load, especially one of that size.

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  • My water heater is on a 30A circuit because they don't make 23-amp breakers. I suspect most houses are like that: there's a bit of available capacity because of rounding to the next larger standard size. Still not enough for a 20A kiln. – Mark Feb 2 '19 at 1:24

Well, if you're willing to install a small breaker box, then install a small subpanel - that's what those are. You need a 4-space main-lug subpanel.

The feed currently to the water heater goes to the main lugs.

A 30A breaker goes to the water heater.

A 20A breaker goes to the #12 going to the kiln.

This will trip the main panel if water heater cycles on while kiln is operating. If you want to interlock it so both loads can't be on at once, get a Siemens panel and this interlock intended for generators.

Big problem though. This panel won't have any neutral wire and it's a matter of time before some clown crams a 120V circuit in there. This will "apparently work" but be dangerous if you're using the built-in neutral bar as the ground bar. So I recommend you don't -- keep it as a neutral bar, just make it an empty one. Remove the ground screw from the neutral bar since it's a subpanel, then install an accessory ground bar and connect the grounds there. Leave the neutral bar disconnected. Bonus points if you find a panel that comes with an accesory ground bar, otherwise, they're like $6.

Breakers and ground bars must match the panel. For all practical purposes that means the same brand and series called for on the panel label, unless you are a genius on applying "classified" breakers, which are those specifically designed for competitor panels and are UL-listed to prove it.

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