Circuit Breaker Size Calculator
The breaker protects the wire, not the appliance.
Work out Circuit Breaker Size. The breaker protects the wire, not the appliance. States the assumption instead of hiding it.
Recommended breaker
16 A
13.04 A load · sized at 13.04 A · IEC (Europe, UK, most of the world)
The breaker protects the wire, not the appliance. That is the sentence to keep hold of: the conductor must be rated at least to the breaker, because the breaker is what limits the current the cable will ever be asked to carry. Continuous loads — anything running three hours or more at a stretch — are sized at 125% of the actual current. Breakers are rated at an ambient temperature they rarely see inside a loaded panel, and sizing to the bare load is how nuisance trips and heat damage both start. The standard series matters and the two are not interchangeable. There is no 15 A device in an IEC panel and no 16 A in a NEC one, which is why the standard is asked for rather than assumed. This is a starting point for a conversation with an electrician, not a substitute for one.
How the Circuit Breaker Size Calculator works
Breaker size for a load, against the IEC or NEC standard series — the two are not interchangeable. Continuous loads are sized at 125%, and the minimum conductor rating is reported alongside, because that is what the breaker actually protects.
Also known as: what size breaker do i need · amps for a 3kw load · continuous load 125 percent · breaker keeps tripping what size
Frequently asked questions
What size breaker do I need?
One rated above the design current, taken from the standard series for your region. The design current is the actual load, raised by 25% if the load runs for three hours or more at a stretch.
Why does a continuous load need 125%?
Because breakers are rated at an ambient temperature they rarely see inside a loaded panel. The margin comes from NEC 210.20(A) and its equivalents, and sizing to the bare load is how nuisance trips and heat damage both start.
Does the breaker protect the appliance?
No — it protects the cable. The conductor must be rated at least to the breaker rating, because the breaker is what limits the current the cable will ever be asked to carry. Appliance protection is a separate device.
Why do IEC and NEC sizes differ?
They are different standards with different preferred numbers. There is no 15 A device in a European panel and no 16 A in a North American one, which is why this asks rather than assuming.
Can I just fit a bigger breaker if it keeps tripping?
No, and it is the single most dangerous thing a non-electrician does. A tripping breaker is reporting a real condition, and fitting a larger one removes the protection from a cable that was never rated for the current.
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