RCD
Residual Current Devices or RCDs are used for protecting circuits against faults causing current to flow to earth, and in some cases protecting users from electric shock.
For more information see http://en.wikipedia.org/wiki/Residual-current_device
Nuisance Trips
One problem with RCDs is nuisance trips. Nuisance trips are when an RCD cuts the power without good reason, ie when no safety risk is present.
There are a number of reasons why these trips occur, and the problem can not be entirely eliminated. Certain strategies are therefore wise to reduce both the occurrence and the consequences of nuisance trips. These are described in the Rewiring Tips article in the following sections:
RCDs and drills
DIYers sometimes put an RCD plug onto their mains drill in the belief that it will stop them being electrocuted if they drill into a cable. In fact it offers no such protection, and tends to encourage less care, resulting in greater danger.
An RCD on the drill plug does not detect any current flowing from wall cable to drill body to user. Nor can it switch this current off. It thus has no effect on such shock scenarios.
An RCD plug on a drill can increase risk more than it reduces it by providing a false sense of security.