Electric Kiln Amps, Breaker & Wire Size Calculator (Voltage Drop, Receptacle, Running Cost)

How it works

I = P ÷ V (single-phase) or P ÷ (√3 × V) (three-phase) · continuous load: breaker and conductor ampacity ≥ 1.25 × I · voltage drop ≈ 2 × I × R × L (single) or √3 × I × R × L (three-phase); keep ≤ 3% · P ∝ V² · cost/h = kW × duty × price

An electric kiln is a large resistive heater that runs for many hours, so electrical codes treat it as a continuous load: the breaker and the wire must be rated at least 125% of the kiln's current, and the circuit must be dedicated. Long cable runs drop voltage, which cuts element power with the square of the voltage and slows firings, so the wire may need to be larger than the ampacity alone suggests. This calculator gives the numbers you and your electrician will check — amps, breaker, wire gauge, drop and receptacle — plus the running cost per firing from the element duty cycle.

Worked example

An 11.5 kW kiln on 240 V single-phase draws 47.9 A. As a continuous load it needs a two-pole breaker of at least 59.9 A → 60 A, and 6 AWG copper (13.3 mm², 65 A at 75 °C); over a 15 m run the drop is about 1.9 V (0.8%), so no upsizing. At 48 A it is above the 6-50 plug's comfortable range and is usually hard-wired to a 60 A circuit. At 65% element duty and $0.16/kWh it uses about 7.5 kWh an hour — about $1.20/h, so a 12-hour glaze firing costs around $14.35.

Frequently asked questions