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What is an RCD?

An RCD (Residual Current Device) is a device designed to provide protection against electrocution or electrical fires, by cutting off the flow of electricity when it detects a fault.

The device detects “leakage” of electric current from a circuit or appliance which can occur when there is a fault within the electrical installation.

How to identify an RCD

RCD test button

RCDs are usually mounted within the consumer unit, however in older installations they may sometimes be mounted adjacent. There are various different types of RCD but the easiest way to recognise them is by the “T” or “Test” button on the front.

Crabtree RCCB.jpeg
Crabtree RCBO
Eaton RCD
Hager RCBO
Hager RCD
MEM Shield RCD

Examples of Residual Current Devices (RCDs) 

How to carry out a functional test on an RCD

It is very important to check your RCDs at regular intervals to confirm that the devices operates correctly. BS7671 IET Wiring Regulations recommend that a check be carried out at a minimum of every 6 months, however, some manufacturers recommend this is done more frequently.  

As demonstrated in the video below, it involves operating the test button which is normally marked “t” or “test”. This should cause the RCD to trip, disconnecting the supply to the protected circuits. 

It is not advisable to re-set the RCD under full load. Therefore, once you have confirmed the RCD has tripped, switch off the associated circuit breakers. Reset the RCD, and then proceed to reset the circuit breakers one at a time.

RCD testing notice

If the RCD does not switch off the supply when the test button is pressed you should seek expert advice immediately. 

When an electrician carries out work on any RCD protected circuit in your property, or when carrying out an Electrical Installation Condition Report, they should also complete a series of additional tests to confirm that the RCD trips within specified parameters and record these for future reference. 

Please feel free to contact us to find out more about how RCDs can protect you and your home.

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