wire choice

[Fumbler]

I have just purchased 100m of 2.5 twin and earth cable for some power points, but was didnt want the added expense of buying 1.5mm for my outside Flour lights. I know i cant drop down to 1.5mm for mains power, but is it okay to upsize to 2.5mm for lighting?

thanks

Fumbler

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[Bob Willson]

Hi fumbler

I am not qualified to answer your question, but I was recently told by an electrician that it is always OK to go to a larger size, but never to a smaller size.

[malb]

Not sure of the context that Bob was given his information by a sparky, but I strongly suspect that it was from the perspective of running a new circuit rather than extending an existing one.
While a larger cable has a greater capacity than the existing 1.5mm2, ultimately what the circuit can safely service will be limited by the weakest part (the 1.5mm2), and someone extending again and tapping into the 2.5mm2 in the future may not be aware that the circuit originates in or steps down to 1.5mm2, with considerably lower current handling capacity. Ideally the breaker/fuse protecting the original circuit is correctly sized for the smaller cable and would provide protection, but it is not unknown to for DIY'ers past, current or future to upgrade the breaker or fit a heavier fuse wire, leaving the origonal 1.5mm2 segment very open to overloading and potentially fire. Also the original poster did not indicate how many external fluoro's he wished to add, so there is potential for these alone to take a circuit already near it's limits over them.
Just my thoughts.

[BobL]

I instead of hardwiring my lights I got my sparky to install unswitched 3 pin sockets (including an earth wire) in the celing near where the lights were located. Each pair of sockets is connected back to a standard light switch by a door and the three pairs run off the same breaker. That way I can mix and match lighting without getting the sparky back - I don't know how legit that is - he did seemed a little reticent to do it but he did sign off on the install.

[Bob Willson]

Not sure of the context that Bob was given his information by a sparky, but I strongly suspect that it was from the perspective of running a new circuit rather than extending an existing one..

Hi Malb

No, it wasn't from that context, but rather that I had put some lights on the end of an existing circuit and used a smaller gauge wire than the one that was currently installed. I did this because I was only installing some 30 watt LED lights. I was told that this was a definite no-go.

[Matt_M]

There is nothing wrong with running 2.5mm for lighting, other then the extra expense of using larger cable.

I have run 2.5mm through my house for both power and lighting.

What you cannot do is add 2.5mm to an existing 10A 1.5mm circuit and then change the circuit breaker to 16A or 20A.

You can run 4mm or 6mm if you want. As long as voltage drop and fault loop impedance are covered, then you are ok.

[soundman]

The minimum size cable that is permitted is detemined by the value of the circuit breaker.
Lighting circuits are generally connected to 10 amp circuit breakers and use 1.5mm2 cable.

No it is not OK to run lighter cable on the end of the run because it will only be lightly loaded.....the fault currents will be the same and if 1.5mm2 cable is what is correct for the circuit breaker lighter cable should not be used....ever.

As for power it is commonly supplied by either 15 or 20 amp breakers, and the minimum size cable is 2.5mm2.

Complications do arise, with long runs due to voltage drop.( the main consideration in the past) and because of the recent ( not that recent) requirements of the "fault loop impedance" clauses in the standard.....clauses half the working electricians don't understand.

cheers