What Is RCD Protection and Which Circuits Need It?

Faulty electrical equipment and sockets cause 350,000 injuries in UK homes every year. Most of these could be prevented with RCD protection.

In this article, we’ll cover what RCD protection is, what it can and can’t protect, and which circuits need it.

What Is RCD Protection?

An RCD (a residential current device) is an electrical safety device that detects dangerous imbalances in electrical currents and disconnects them automatically. The speed at which this is done matters because it can cause a fault current before it is able to start a fire or cause serious harm to anyone. An RCD is usually mandatory to have in any commercial premises as per BS 7671 Wiring Regulations.

To understand why having RCD protection is important, it helps to understand how electricity is supposed to flow. When you turn on an appliance, electricity will flow to it through the live wire and back out through a neutral wire. In a system that’s working and is safe, the amount of electricity going in should be exactly the same as what’s coming out. If less is coming out than what went in, it means there is a leak somewhere. An RCD should notice even a tiny drop in the returning electricity and shut the power off.

An RCD is monitoring this all the time. When it detects a residual current above its rated threshold, it will trip the circuit in a fraction of a second, which is usually fast enough to prevent a lethal electric shock in most cases.

What Does an RCD Protect Against?

There are 3 types of hazards that an RCD is designed to protect against.

Electric shock from direct contact

If someone touches a live conductor (could be drilling into a cable or touching a faulty appliance) the current will seek a path to earth and that can be through the body. The RCD protection will detect that and disconnect the supply

Electric shock from indirect contact

Indirect contact can happen if you touch an exposed conductive part that has become live because of a fault. For example, if your washing machine breaks and the drum is live, touching it could mean you receive a shock. An RCD should kick in in these scenarios, too.

Electrical fire and earth faults

An RCD should stop hidden electrical dangers before they cause secret fires, hidden leaks or gradual heating that can build up.

Hidden leaks can leak pretty much silently out of damaged wires, and this small leak that’s invisible can then slowly build up heat. This heat can build up and become hot enough to start a fire inside your walls or ceilings, where you cannot see it until it’s too late.

What Does an RCD Not Protect Against?

Having RCD protection is very important, but it doesn’t protect against everything.

• live-to-neutral faults: if both fail simultaneously, an RCD might not detect the imbalance and won’t automatically trip.
• Overcurrent protection: You need an MCB (miniature circuit breaker) or a fuse for this.
• Protection against voltages on the neutral conductor in certain supply configurations.

What Circuits Need RCD Protection?

The rules around this are set out by the UK’s official electrical standards. The main legislation is called BS7671, which was updated in 2022.

Circuits that need RCD protection include:

• Sockets
• Bathrooms
• Kitchens
• Garages
• EV charging points

Circuits where it’s strongly recommended:

• Light circuits indoors
• Cookers and hobs
• Smoke and carbon monoxide alarms

Commercial RCD Requirements

The rules regarding RCD protection differ for commercial premises. A business can sometimes not be legally required to have an RCD, but only on specific pieces of equipment, if the power turning off unexpectedly would cause a major hazard. The premises must have a sign-off by a qualified commercial electrician and a risk assessment written up.

RCD Protection in Rented Properties

For landlords in England, the law requires that all electrical installations be inspected and tested at intervals of no more than 5 years by a qualified electrician. The Electrical Installation Condition Report (EICR) will identify any absence of required RCD protection as a coded defect.

So, for landlords, your EICR certificate should show:

• RCD protection on all socket circuits
• RCD protection on outdoor circuits
• Bathroom circuits compliant with BS7671
• If you have EV charging circuits, they need to be protected by a Type B RCD
• Concealed cables in walls at a shallow depth protected by 30mA RCD
• Evidence that RCDs have been tested and are functioning correctly

How to Test Your RCD

You should be testing your RCD every 6 months. Here’s how:

• Find your fuse board, which is usually in the hallway, under the stairs or in a utility room.
• Find RCD switches (they’re wider than standard MCBs and have a small button on the front that says the letter t or test.
• Reset the RCD by switching it to ON. If it won’t reset or trip, then you will need to get in touch with a qualified electrician.
• Keep a note of date tested.

RCD Protection FAQs

Do commercial lighting circuits need RCD protection?

Usually, yes, most commercial lighting circuits do need RCD protection or it’s strongly recommended to have it for safety reasons. The exact requirements will depend on the type of building, how the wiring is installed and specific electrical regulations, which a qualified electrician will be able to determine.

Can I add RCD protection to my fuse board?

In most cases yes you can. A qualified electrician can retrofit RCD protection by replacing existing MCBs and a residual current breaker. This will depend on the age, condition and configuration of the board, as sometimes a full replacement is safer.

Do RCDs need to be replaced?

There’s no legal requirement as to when it needs replacing, but if it’s failing tests, trips frequently or is over 20+ years old, it should be tested with calibrated equipment and replaced if needed.

Do I need an electrician to install an RCD, or can I do it myself?

This wouldn’t be a DIY job, as your fuse board is legally classified as work that needs to be signed off by a qualified electrician who is NICEIC-registered, as they will handle all the paperwork automatically.

What’s an MCB?

An MCB stands for a miniature circuit breaker, and it’s the row of small switches inside your fuse box. Each one protects a different circuit, which is usually one for lights, one for sockets, one for your cooker, etc. If too much electricity is flowing through a circuit, the MCB flips itself off to prevent the wiring from overheating and potentially causing a fire. The MCB is not what protects you from electric shock, as that’s what the RCD is for.