Hi, I was wondering If there was a limit to how long a trailing socket cable can be?, as I cant find one long enough so wouold have to fit a new cable to one of the trailing sockets I have.

thanks in advance

Gordon

The limit depends on the cable being used. For a 'standard' 1.5mm c.s.a. cable you can use it for up to 3kW load at around 50m length. USe a 'thicker' cable (say 2.5mm c.s.a) and the length increases considerably.

Bear in mind that, to use the cable lengths at these ratings they CANNOT be coiled onto a drum during use as they act as 'heaters' and can melt the cable

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What one has to ensure is if there is a short circuit the protective device will open. This includes both line to neutral and line to earth. The latter can be covered by using a RCD.

So what we look at is the loop impedance. A 13A fuse can have a loop impedance as high as 2.42 ohms and a 3A fuse would be 16.4 ohms. Since the socket (assuming normal ring main) is allowed 1.44 ohms for a 13A extension lead you can have 0.98 ohms so round figures 1 ohm.

1.5mm cable is around 0.029 ohms per meter so simple maths 33.7 meters maximum. With 2.5mm at 0.018 ohms per meter this goes to 54.4 meters. In real terms one would not want to go to limit as also there would be a volt drop problem.

Using smaller fuses one could go longer but the problem is to ensure it is never replaced for a bigger one so the fuse size needs to be well marked. Also of course where radial supplies are used the the socket supplied from a 16A MCB could be rated 2.875 ohms take that from the 13A fuse of 2.42 and you end up with a minus figure. Hence why so many are against Part P which is making people use extension leads rather than a proper extension.