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—Wiring and circuits

Circuit breakers, explained

A circuit breaker is there to protect the cable in the wall. When it trips, it is telling you the cable was at risk.

Each circuit in a distribution board is protected by a breaker sized for the cable and the circuit. If too much current flows for too long — an overload — the breaker switches off before the cable overheats. If a sudden large current flows — a short circuit — it switches off almost instantly.

Wiring guides explain how circuits are put together and changed, so a quotation or a recommendation is easier to follow.

Breakers have ratings that match the cables they protect. Replacing a tripping breaker with a larger one may stop the tripping, but it removes the protection and lets the cable overheat. The right response to frequent tripping is to find out why, and change the circuit or the load if necessary.

01In short

The points that matter most

  • They protect cables

    Breakers are sized to the cable, not the appliance.

  • Overload and short circuit

    Two different events, both causing trips.

  • Never upsize to stop trips

    It removes protection.

02Detail

When breakers trip

  • Overload

    Too many appliances on one circuit.

  • Short circuit

    A fault creating a sudden large current.

  • Ageing devices

    Occasionally a breaker itself becomes faulty.

  • Breaker curves

    Breakers are made with different trip characteristics; some motors and transformers need a type that tolerates their start-up surge.

03Checklist

If a breaker trips

  • Reset once

    After unplugging likely loads.

  • Leave it off if it trips again

    And have it checked.

  • Note what was running

    To help diagnosis.

04Questions

Questions people ask

Can breakers wear out?
They can become faulty over time; testing shows.
Why is my breaker warm?
Heavy load or loose connections; have it checked.
What do the numbers mean?
They indicate the current rating and trip characteristics.
Why do breakers trip when the AC starts?
Start-up current can be high; a correctly sized circuit and breaker type usually cope, and repeated trips need checking.

05Related

Related guides

This guide sits under electrical wiring. All topics are on the guides page.

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Breaker tripping often?

Tell us which circuit and what was running. We will check the circuit and load.

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