pat testing questions

First thing to realise is that RCDs and related  devices like RCBOs have two current ratings, a maximum load current which may be 32A, or 16 or 13A for a plug-in one, and a maximum fault current, which is much lower, 30milli-Amps or less for safety of life applications, like sockets. This much lower current represents the largest fault current, normally to earth, but could be to anywhere that is not a legitimate load, as inside the RCD it is measured as the difference of the live current going out and the neutral current returning - so an RCD does not need an earth connection itself to detect a live to earth fault. 

The idea is that if you are in your bare feet on the lawn and anything more than 30mA flows out of say your defective hedge trimmer cable or whatever, and goes up your arm to and down too ground via your feet, the RCD will trip, cutting the supply before fibrillation of your heart really gets going. It does not stop it being !!!##!!!  painful though, and you may be hurt if the muscular convulsions  make you fall over something hard or sharp but the chances of survival are greatly improved.


So for a socket supplying equipment that may be hand held, an RCD with a 30mA trip  current, or less,  is the expected answer.

When I asked above if you understood fuses and breakers this is sort of what I meant.

Other RCD ratings exist for special applications, but they are not for safety  of life.

First thing to realise is that RCDs and related  devices like RCBOs have two current ratings, a maximum load current which may be 32A, or 16 or 13A for a plug-in one, and a maximum fault current, which is much lower, 30milli-Amps or less for safety of life applications, like sockets. This much lower current represents the largest fault current, normally to earth, but could be to anywhere that is not a legitimate load, as inside the RCD it is measured as the difference of the live current going out and the neutral current returning - so an RCD does not need an earth connection itself to detect a live to earth fault. 

The idea is that if you are in your bare feet on the lawn and anything more than 30mA flows out of say your defective hedge trimmer cable or whatever, and goes up your arm to and down too ground via your feet, the RCD will trip, cutting the supply before fibrillation of your heart really gets going. It does not stop it being !!!##!!!  painful though, and you may be hurt if the muscular convulsions  make you fall over something hard or sharp but the chances of survival are greatly improved.


So for a socket supplying equipment that may be hand held, an RCD with a 30mA trip  current, or less,  is the expected answer.

When I asked above if you understood fuses and breakers this is sort of what I meant.

Other RCD ratings exist for special applications, but they are not for safety  of life.