Load & Breaker
Enter the load (W or VA), voltage and number of phases and I compute the current, the minimum breaker by the 80% continuous-load rule and the recommended standard rating (IEC/NEC).
The breaker must sit above the load current with headroom.
Series ratings
| Rating | Max continuous load (80%) | Status |
|---|
How it is computed · current, 80% and rating
1. If the load comes in W I
turn it into apparent power by dividing by the power factor:
VA = W / PF. If it already comes in VA, it
goes straight through.
2. Load current. Single phase:
I = VA / V. Three phase (V = line-to-line):
I = VA / (√3 · V).
3. The 80% rule for a continuous load
(runs ≥ 3 h): the breaker must not carry more than 80% of its
rating, so breaker ≥ I / 0.8. For a non-continuous load
breaker ≥ I is enough.
4. I pick the next standard
rating above that minimum, from the IEC 60898 or NEC 240.6
series. Also check the conductor can carry that current.
Runs locally in your browser · no sign-up · nothing leaves your browser. Design reference; verify against your local code and the conductor.