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The Importance of RCD Protection

Updated: Jan 21, 2019

Ever had a tradesman come to your property and mentioned an RCD?


What's an RCD? Why do I need one? Do I actually need one?


Well the answer to that is... It's hard to explain, to protect you and yes!


A 2 Pole Single Phase RCD

So Lets Explain

A Residual Current Device (RCD) is a life saving device. It detects an imbalance within the circuit(s) it's protecting. Should a fault or an electric shock occur, it operates, disconnecting the electricity supply within milliseconds.


Ever heard only half an Amp can kill you?


Well an RCD providing 'Additional Protection' Trips below 0.03 of an Amp.


50 Volts is what we call 'Safe Touch Voltage'. Meaning anything below 50 Volts won't hurt you. So if we apply some quick math...



Ohms Law,


V (Voltage) = I (Current) x R (Resistance)


Rearrange that to I = V / R


50 / 1667 = 0.029


30 milliamps




All circuit should now be RCD protected, especially Sockets and accessories in 'Special Locations' such as a Bathroom or Outside.


BS7671:2018 18th Edition States:


411.3.3 - In AC systems, additional protection by means of RCD with a rated residual operating current not exceeding 30 mA shall be provided for:


1.) socket-outlets with a rated current not exceeding 32A, and

2.) mobile equipment with a rated current not exceeding 32A for use outdoors.


411.3.4 - Within domestic (household) premises, additional protection by an RCD with a rated residual operating current not exceeding 30 mA shall be provided for AC final circuits supplying luminaries


Different Types Of RCDs

RCDs come in many forms. These include (but not limited to) 2 Pole RCDS, RCBOs, Plug in RCDS, RCD Sockets and Spurs and many more. To choose the right one can be complicated, so it's always best to contact a qualified Electrician.


How Do I Check If I Have One?

To check if you have fixed RCD protection, go to your consumer unit (Fuse Board), if there is a device with a push button marked ‘T’ or ‘Test’ then you have one. If an RCD is fitted, there should also be a label on or near the consumer unit stating so.


Anyway, without boring you too much

Do you need an RCD?


The answer... YES!


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