Do I Need an RCD?

RCDs protect humans against electrocution in a way that fuses and circuit breakers do not. For more information about the differences and applications, read our guide.

If you have a new circuit installed, or a circuit is substantially modified, you may be required to have an RCD fitted under the Building Regulations (Part P) or BS7671 wiring regulations. This is a legal requirement.

In domestic properties, situations requiring mandatory RCD protection include:

• Properties supplied by a TT earthing arrangement (one with a local earth terminal, as opposed to an earth being provided by the distributor). This typically includes rural locations fed by overhead cables. In this case, a 100mA RCD should be used for all circuits other than those below, which require a 30mA RCD.
• Socket outlets for general use, where a device can be routinely plugged in or disconnected.
• Any location with a bath or shower.
• Circuits supplying equipment for use outdoors - for example, outside sockets, or sockets in a garage used to supply a jetwasher or lawnmower.
• Cables installed in walls or partitions where the installation depth is less than 50mm, or where the wall contains metal parts other than nails/screws.

RCDs can be fitted to specific circuits, such as power showers, if you have an older fuseboard which does not support RCDs. Alternatively, you may consider replacing a fuseboard with a more modern consumer unit which incorporates full RCD protection.

This is not an exhaustive list. If you are unsure, contact us for expert advice.