RCD replacement

An RCD protects several circuits at once against leakage current but has no overload protection of its own. That is handled by the individual circuit breakers, the modern replacements for fuses. If the RCD trips, all circuits behind it go off at once, leaving, for example, a whole floor without power.

A combined circuit breaker (RCD+MCB) combines both in one module, per circuit: protection against shock and protection of the wiring together. If something goes wrong in the bathroom, only that circuit goes off and the rest of your home stays on. They cost a little more per unit, but offer more convenience and certainty. We give honest advice on what makes sense in your consumer unit.

The 30 mA refers to the leakage current difference at which the RCD trips: 30 milliamps. This is deliberately low, because a current through your body can become dangerous at that level. By switching off within milliseconds, the RCD keeps the duration and strength of any shock below the threshold that your heart and muscles can withstand.

This is called personal protection: the RCD is not there to protect your appliances, but to protect you and the people in your home. That is why every circuit that people can come into contact with must be protected by a 30 mA RCD. An older 300 mA RCD only protects against fire, not against a shock, and is therefore not adequate as personal protection.

For standard household circuits, a type A RCD is the norm. It detects both normal AC leakage and the pulsating DC leakage that modern electronics can cause. For virtually everything in the home, type A is the right choice.

Type B is a heavier version that also detects pure DC leakage and is considerably more expensive. Type B was often mentioned for EV chargers, but many modern chargers already have built-in DC detection, which means an ordinary type A RCD is usually sufficient. We check the specification of your charger and advise on what is genuinely needed, so you do not pay unnecessarily for type B.