> First, is there a limit to the total amperage of circuits in relation
> to the main service amperage?
There's probably a code restriction on the max, but nothing you've
said makes me think that you're past it. I have a 60A subpanel
in my garage, and there's a 50A circuit to run the (someday) TIG
along with a whole slew of double/single 20A. The main is what matters;
it needs to be sized so you don't melt wire when you turn on too
many things are once. The box bus should be sized for a fully
stuffed panel.
> Second, since I don't have a double slot available, I think I would
> either need to add a sub-panel (and move at least one existing
> circuit over there along with the new one for the kiln), or replace
> the main panel with a bigger one. Are those my options, without
> shedding an existing circuit?
Get a pair of half-width breakers. Depending on the age of your panel,
this may be hard or easy. Basically you take two of your existing breakers
and replace them with a unit that only takes up one slot. Perfectly
legal, but it can be difficult/expensive to find the right unit
(you might have to go to a specialist if your panel is more than
10 years old). The only downside to this is that the balance across
phases has changed - usually not a big deal if most of your load
is intermittent.
Voila. You have two slots. Continue.
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