Tutorials

RCDs: what they are, where they are required and why they trip

An RCD cuts power before current runs through a person. Where the Latvian code requires one, which type to pick and what to do when it trips.

Sep 17, 2026 · NextTek

Short answer: an RCD (noplūdes automāts in Latvian) compares the current going out on the phase with the current coming back on the neutral. If the difference exceeds its setting, say 30 mA, it cuts the circuit in a fraction of a second. That difference is current escaping through a damp wall, a faulty device or a person.

How it differs from a normal breaker

A normal breaker trips when the current is too high for the wire: overload or short circuit. It does not react to 30 mA flowing through a person. An RCD, in turn, does not protect against overload. So a panel needs both, or one combined device called an RCBO.

Where the building code requires it

Since the 2025 amendments, LBN 261-15 requires:

an RCD of 30 mA or less for general-use sockets up to 32 A used by people without electrical training (point 28.1);
the same for outdoor sockets up to 32 A;
the same for lighting circuits in household installations;
for a detached house, a 300–500 mA RCD in the main incoming panel or an equivalent solution (point 28.2).

The code covers design and installation, so new wiring and rebuilds. It does not force you to redo an existing flat. But if a renovation replaces the panel or adds new circuits, the new part already has to comply.

Which type to pick

Point 28.3 says to choose the type by the connected equipment. In plain terms:

AC sees only pure alternating current. Often not enough for modern electronics.
A also sees pulsating direct current. The usual choice for sockets and lighting.
F is for devices with a frequency converter, such as a washing machine or heat pump.
B also sees smooth direct current. Some EV chargers and solar inverters require it if they have no protection of their own.

The device manual has the final word. If a charger or inverter manual says “type B”, a type A RCD may fail to trip there.

Why the RCD trips

Unplug devices one at a time

Switch everything off the circuit and reset the RCD. Then plug devices back one by one. The usual culprits are a water heater with an old element, a washing machine, a dishwasher and an extension lead on the balcony.

Look for moisture

An outdoor socket after rain, a bathroom fan, a basement light. If it trips only after rain, the fault is usually moisture, not the RCD.

Do not hold the lever up

If the RCD trips again straight away, the circuit has a leak. Do not hold the lever up or tape it. That is exactly what it protects you from.

Check for a shared neutral

In old wiring the neutrals of two circuits are sometimes joined. Then the RCD trips when a light goes on in another room. An electrician finds it by measuring, not guessing.

Press the T button

An RCD has a T or Test button. It creates an artificial leak, and the RCD must trip. Manufacturers recommend pressing it regularly, often every six months; the manual says exactly. If it does not trip after T, replace it.

What it costs and what to do

The device itself is not expensive. The work depends on the panel: whether there is room, whether the circuit neutrals are separated and whether the old panel is safe at all. An exact price is possible after seeing the panel or a good photo.

A NextTek electrician looks at the panel, fits an RCD of the right type and finds out why it trips. More on the electrician page. If the wiring is old, start with a wiring inspection.

Sources: LBN 261-15 (points 28.1–28.3, amended by Cabinet Regulation No. 355 of 17 June 2025). Checked in October 2026.

Common questions

What is an RCD?

A device that compares the current on the phase and the neutral. If part of it escapes elsewhere, for example through a person or a damp wall, it cuts the circuit in a fraction of a second.

Is an RCD mandatory?

For new wiring and rebuilds, yes: LBN 261-15 requires 30 mA or less for sockets and lighting. Existing wiring is not forced to change, but adding one is worth it.

How is an RCD different from a normal breaker?

A normal breaker protects the wire from overload and short circuit. An RCD protects a person from leakage current. Neither replaces the other, so you need both or a combined device.

Why does the RCD trip?

Usually the fault is a device or moisture: a water heater, a washing machine, an outdoor socket after rain. Unplug devices one at a time. If an empty circuit still trips, it needs an electrician's measurement.

Which type: AC, A, F or B?

Usually A for sockets and lighting. F for a washing machine or heat pump with a frequency converter. For an EV charger or inverter, whatever the manual says, often B.

How many mA does a house need?

30 mA or less for sockets and lighting. In a detached house's main incoming panel, the code asks for a 300–500 mA RCD or an equivalent, which also guards against fire.

How often should I press the T button?

As often as the manufacturer's manual says, often every six months. If the RCD does not trip when you press it, it no longer protects you and must be replaced.

Can I fit an RCD myself?

It is work inside a live 230 V panel, and the code leaves installation to a certified specialist. If you do not know phase from neutral or how to separate them per circuit, call an electrician.

Want this in your home?

Tell us what you have now. We will answer with a next step, not a catalogue.