Length of Spur!

[pen_fold]

I Have been reading the posts on spurs and general info on them on other websites, they say that a spur that is too long can be dangerous!! But cannot find out how long is too long! One of the posts on here suggests using 4mm cable instead of 2.5mm if the spur is going to be very long, is this correct?????

I am planning on running a spur as my earlier post says, from an existing (suitable) socket under the wood flooring to a FCU. In all it will probably be about a 3m run, is this too long? If not, should I use 2.5mm or as the other post suggested 4mm cable????

Thanks

 

[dingbat]

The longer a conductor, the greater the resistance. There are two main potential (geddit? ) problems with this: One is volt drop, which is not normally an issue in a bog-standard house. The other is the value of the impedance of the circuit - if the impedance is too high the circuit protective device may not operate correctly to disconnect the fault.

You should, of course, have the necessary test equipment to verify that what you intend to do is safe, but if this spur is inside a normal-sized house I very much doubt that your 3m will be significant. (If it was, it would raise questions about the design of the circuit you are spurring from!)

 

[pen_fold]

Thanks, for that!

So would it be safer to keep with the 2.5mm cabling for the spur as normal or upsize it to 4mm as I read in a reply to someone else's post????

 

[dingbat]

As long as it's a normal spur supplying one twin socket then use 2.5. You shouldn't really mix cable sizes on any circuit without good reason and suitable precautions.