How many RCD Sockets can I fit?

[dogberry]

I hope you guys can give me some advice.

I have an attached garage with three double sockets. These are powered from a garage CU on a Radial circuit. There is no built in RCD in the CU.

As I use the garage for plugging in lawnmowers, drills, sanders and other bits I thought it best to fit RCD sockets. I was just reading the instructions that came with them and it states.

"If a second RCD is fitted in the same circuit it may not be possible to predict which will trip in the event of a fault."

Is this still safe? I assume it means that if the last socket in the line is being used and a fault occurs then any one of the three socket might trip but the power will still be cut to where the problem is. Is this correct or should I fit a RCD spur between the CU and the first socket instead?

Many thanks

 

[SparkyMarky]

If you get a fault then only the socket which your appliance is plugged into will trip. RCD sockets don't cut the power to the whole circuit, only to the appliance actually plugged into the socket.

What your instructions mean is that if you wired the socket into a RCD protected circuit (RCD in the main consumer unit at or a smaller CU local to the garage for example) it possible that the circuit RCD could trip before the socket RCD if you get a fault. There are ways of ensuring the correct discrimination in the event of a fault (time delay RCDs for example) to meet current wiring regs but in your case as you haven't got a RCD protecting the circuit it's not a problem anyway.

 

[dogberry]

Many thanks SparkyMarky.