# Why does it “trip”?

> Why a distribution box “trips”: 30 mA RCD and circuit breaker explained simply. Faulty appliance or overloaded circuit?

Source: https://www.darkside-energy.com/en/did-you-know/why-it-trips/ · Dark Side Energy · Updated: 2026-10-06

8 May 2017 · 1 min read · Updated 6 October 2026

- The 30 mA RCD cuts the power when an appliance leaks current: it protects people.
- The circuit breaker cuts the power in the event of an overload or a short circuit: it protects the installation.
- When it trips, the box has done its job: look for the faulty appliance or spread your appliances over several circuits.

I think the sentence I have heard most often in our trade is: “There's a problem with your box, it keeps tripping!”

Yes, for most clients, when “it trips”, it is the fault of the electrician or of their distribution box.

## Back to basics

A distribution box is fitted with two main protective devices:

- a **30 mA RCD**, which protects people against leakage current;
- one or more **circuit breakers**, which protect the circuits against a current higher than they can withstand.

So when an RCD has tripped, it means that one or more appliances plugged into the distribution box have a fault, often a current leakage problem. This fault, or these faults added together, exceed 30 mA, so the RCD cuts the power for safety.

The circuit breaker, for its part, trips as soon as the current flowing through it exceeds the current it is rated to let through (expressed in amperes). It also protects against short circuits (its breaking capacity is expressed in kiloamperes).

## To sum up

Either you have one or more faulty appliances, or you have plugged too many appliances into the same circuit.

> As for the box, it has either saved your life or saved your installation.

Check the power of your appliances before plugging them in.

[Run a power assessment](https://www.darkside-energy.com/en/power-assessment/)

[Cable size depends on current, but also on length!](https://www.darkside-energy.com/en/did-you-know/cable-size/)

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