The 80% rule in one line
The National Electrical Code calls a load that runs at full current for three hours or more a continuous load, and sizes the circuit for it at 125% of that current. That is the same as saying the load may use only 80% of the breaker’s rating. A kiln firing runs for hours, so kiln makers and electricians treat it as continuous.
| Breaker | Continuous limit (80%) | Largest kiln draw |
|---|---|---|
| 15 A | 12 A | 12 A |
| 20 A | 16 A | 16 A |
| 30 A | 24 A | 24 A |
| 40 A | 32 A | 32 A |
| 50 A | 40 A | 40 A |
120 V “plug-in” kilns
Plug-in does not mean any outlet. A 120 V kiln that draws 15 A needs 15 × 1.25 = 18.75 A of circuit, which means a 20 A circuit, not the 15 A circuit behind most household outlets. Many small kilns are specified for a dedicated circuit with nothing else plugged in, and the plug on the cord tells you which receptacle the maker expects.
240 V kilns
Larger kilns run on 240 V (or 208 V in some buildings) and need a dedicated circuit sized for their amps. A kiln that draws 48 A needs 48 × 1.25 = 60 A of circuit, which is beyond this checker’s 50 A option. Wire gauge also depends on distance from the panel, so the electrician sizes the whole run, not just the breaker.
208 V and 240 V are not interchangeable. A kiln built for 240 V on a 208 V supply heats more slowly, so many models come in both versions: order the one that matches your building.
What to tell your electrician
- Kiln model, voltage, amps and phase (homes are almost always single-phase)
- The receptacle or hard-wiring the manual specifies
- Where the kiln will sit and how far that is from the panel
- Clearances the manual asks for around the kiln