Sockets on radial - extra rcd needed?

[altnipper]

Hi, I have some stables with quite a long run to a socket, I want to add a line of other sockets off the main wire before the socket. The wire is 2.5mm2, 20amp circuit with rcd at the board.

My questions are these:

It is in a shed with power tools - I like safety so i was going to add another RCD in close to the 4 sockets as a failsafe. Is it worth it, if i put an RCD at the green socket (ie this is a double socket with rcd protection) does this then cover the sockets downstream from it or would they all need to be separate RCD sockets? I presume they would.

To get over this I thought of putting an inline RCD at the yellow cross - I think this wouldn't work tough as if the circuit is pulling more than 13amps then it would trip - I wouldn't find any inline ones that are more than 13amps (I probably wouldn't use that at one time anyway but it would be annoying if tripping)

Final question - I know there is not an infinite amount of wire you can use in a radial circuit - the length is about 27 meters to the current socket which works fine. Is the total length the sum of the wiring or the most distant socket?

Thanks in advance.

 

[Ragnar_AT]

The maximum length is the wiring to the most distant socket.

Do you want the second RCD in case the one at the CU fails? You can do that but it’s usually considered unnecessary. If you insist you could have a standard RCD in a small enclosure like a garage CU.

 

[altnipper]

Thanks for the reply - the CU that feeds this is in one of the stables already at the other end. So essentially it would be just repeating what is already there I think - so yes I suppose a small CU in the room that has the extra sockets - I was just thinking there might be something simpler. I guess the RCD's in the sockets are but they are quite expensive.

 

[Taylortwocities]

The maximum length is the wiring to the most distant socket.

The distance is the measurement from the SOURCE (the incoming mains) to the last socket. The volt drop is the issue and is a function of maximum current, distance, and cable area.

There is absolutely no point having a second RCD. There will be no telling which one will trip, it could be both.

 

[EFLImpudence]

It is in a shed with power tools - I like safety so i was going to add another RCD in close to the 4 sockets as a failsafe. Is it worth it, if i put an RCD at the green socket (ie this is a double socket with rcd protection) does this then cover the sockets downstream from it or would they all need to be separate RCD sockets? I presume they would.

It would only cover what was plugged in to the socket.

To get over this I thought of putting an inline RCD at the yellow cross - I think this wouldn't work tough as if the circuit is pulling more than 13amps then it would trip - I wouldn't find any inline ones that are more than 13amps (I probably wouldn't use that at one time anyway but it would be annoying if tripping)

If you just want fail-safe then you might as well have two RCDs in the consumer unit.

Final question - I know there is not an infinite amount of wire you can use in a radial circuit

Well - there sort of is within reason. You can have many branches.

- the length is about 27 meters to the current socket which works fine. Is the total length the sum of the wiring or the most distant socket?

For electrical considerations it is the length of the current path to the end of each branch.

 

[altnipper]

Ok great thanks