What is an RCD?

What is an RCD?

RCD is short for Residual Current Device, it's one of the most effective ways to protect yourself from an electrical accident. As we all know, electricity can cause catastrophic damage, in some cases it can be fatal.  By installing a Residual Current Device into your electrical system, you decrease the risk of an electric shock by a significant amount.

How does an RCD work?

As previously mentioned, RCD’s are designed to protect you against electric shocks. But how do they work? An RCD continuously monitors the electric current flowing through live and neutral wires. The device will be able to identify any faults. For instance, If the live and neutral current becomes unbalanced, the RCD will detect this and cut the power instantly.

Types of RCD’s

Fixed

Commonly found within a fuse box. Fixed RCD’s deliver the best protection against electrocution. Furthermore, fixed RCDs protect individual circuits and more complex setups which are part of multiple circuits.

Portable

Portable RCD’s can be relocated to wherever they are required. These RCDs are generally used when installation options are limited. For example, on a constructions site. Portable RCDs are plugged into a wall socket outlet, from which an electrical device can be plugged into it.

Socket Outlet RCD

A socket outlet RCD will replace a standard socket outlet in your home or business. These outlets provide a much safer option for working with electrical devices. In addition, Socket outlets are commonly found in outdoor extensions cables.

Choosing the Right Type: AC, A, or B?

RCDs are not one-size-fits-all. They are classified by the types of residual current they can detect. Choosing the wrong type can leave a commercial facility unprotected.

• Type AC: Historically the most common, designed to detect sinusoidal alternating residual currents. However, modern offices filled with electronic equipment can blind Type AC RCDs, rendering them useless.
• Type A: These detect alternating currents as well as pulsating direct currents. They are now the standard baseline requirement for most modern circuits supplying IT equipment, electronic ballasts, and office appliances.
• Type B: Crucial for industrial environments, electric vehicle (EV) charging points, and specific data centre infrastructure. They detect alternating, pulsating direct, and smooth direct residual currents.

What can trip an RCD?

RCDs are considered to be very reliable devices. In fact, studies have shown they prevent electric shocks in around 97% of all cases. However, as its not a 100% you should always be cautious when working with electrical appliances and RCD’s. Below are 2 of the best practices we wish to highlight.

Troubleshooting Guide for "Nuisance Tripping"

When an RCD trips, it is doing its job—either protecting against an active earth fault or reacting to cumulative leakage. If an entire section of your office suddenly loses power, use this systematic approach to identify the culprit:

Disconnect Everything: Unplug all appliances and office equipment from the sockets on the affected circuit. Simply turning them off at the switch is sometimes insufficient; physically pull the plugs out.

Reset the RCD: Go to the distribution board and switch the RCD back to the "On" position. If it trips again immediately with nothing plugged in, the fault is likely within the fixed wiring itself, requiring an engineer.

Reconnect One by One: If the RCD stays on, begin plugging your appliances back in, one at a time. Monitor the board.

Identify the Trigger: The specific appliance that causes the RCD to trip the moment it is plugged in or switched on is your faulty device. This is common with older kettles, refrigeration units, or faulty laptop chargers.

Testing an RCD device

All Residual Current Devices are designed with a built-in test button which enables the user to test the device before carrying out any work. We highly recommend all users to complete a test on each RCD once every three months. This regular testing will allow you to stay on top of potential issues. If the test button does not cut the power, you must contact an electrician to investigate this further.

Check your wiring

To prevent electrical accidents, any electrical installations including RCD’s must be checked every 5 or 10 years. Over time electrical writing can deteriorate causing circuits to easily malfunction. Therefore, its crucial for you to cover every base instead of solely relying on an RCD device.

The Importance of RCD Testing for Businesses

An unmaintained RCD is a ticking liability clock. For commercial properties, the Electricity at Work Regulations 1989 require that electrical systems are maintained to prevent danger.

Routine testing involves pressing the physical 'T' or 'Test' button on the unit every six months, alongside formal Electrical Installation Condition Reports (EICR) and PAT testing. Regular testing ensures that in the event of a fault, the device cuts the power within 40 milliseconds, protecting your staff from fatal shocks and protecting your business infrastructure from electrical fires.

RCDs and UK Wiring Regulations (BS 7671)

Under the IET Wiring Regulations 18th Edition (and its subsequent amendments), the requirements for RCD protection have become significantly stricter. It is no longer just about residential safety; commercial and data environments face rigorous compliance standards.

Socket Outlets: Regulation 411.3.3 mandates that all socket outlets with a rated current up to 32A must have RCD protection if they are used by ordinary persons. This applies directly to standard office desk power modules and commercial workspaces.

Mobile Equipment: Any mobile equipment rated up to 32A used outdoors must be protected by a 30mA RCD.

High-Density IT Environments: In modern server rooms and structured cabling environments, standard RCDs can suffer from "nuisance tripping" due to protective conductor currents (earth leakage) from computers and IT hardware. To comply with Section 531.3.2, circuits must be divided so that the predictable leakage current does not exceed 30% of the RCD's rated residual operating current.