I understand that an RCD device helps to provide protection against electric shocks when completing a circuit between Live and Earth wires, where the Neutral and Earth wires are separated before being wired into the consumer-unit/distribution-panel.

My understanding is that the RCD device works by detecting a difference between the current in the Live wire and the return current in the Neutral wire. When a tolerance is exceeded the RCD device opens the circuit, to prevent further current flow.

Does an RCD device provide any protection if the electric shock occurs between the Live and Neutral wires, given the current will still be returning on the Neutral path?


2 Answers 2


If all of the shock current flows between live and neutral then there is nothing the RCD can do. It does not know that the load it is presented with is a human body rather than a peice of electrical equipment.

However it is worth noting that the most dangerous shocks are those that pass through the core of your body. Unless you do something really stupid like grabbiing the live with one hand and the neutral with the other, live to neutral shocks are most likely to be limited to an extremity, whereas live to earth shocks have a much greater chance of passing through the core of your body.


No, it does not.

It only detects "missing" current that must be going elsewhere (to ground.)

You can plug a 0.1W night-light or a 1500W hairdryer into a RCD outlet - as long as no current comes up "missing", it will happily power it.

Note that a RCD outlet can also open if the "hot" comes from something else (like a previously-wired lightbulb) and that device causes an imbalance (finger in light socket.) In this case, you'll still get shocked, and the (new) outlet will switch off (not very helpful!) If you have RCD's in the fusebox, then it would protect the whole house, and the power would "go out." (Note that in many homes, the fusebox has two sections - so perhaps only "half" the power in the house goes out.)

I once replaced traditional outlets with GFCI for a washer and dryer, and they would trip at odd hours. An old fridge nearby was found to be the culprit and it was on the same circuit as the GFCI's. It had a small internal leakage current to the chassis which varied by state of the automatic defroster.


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