cable size

paddy1 · 11 Jan 2005

I have recently bought cable, a new ceiling rose and a switch to install a light into my roof space. When I went to install this and loop it into the last light on the upstairs lighting circuit I realised that the cable is 2.5mm and not 1.5mm. Would it be ok to go ahead and use this or will it be a hazard or cause the 5Amp fuse in this lighting circuit to blow?

Thanks.

dingbat · 11 Jan 2005

You shouldn't really mix cable sizes on a circuit, but going up a size is not a hazard. (the cable itself is not responsible for the load) You might have to swear a lot when you're trying to terminate that size cable in a ceiling rose, though... especially the one you're taking your supply from.

If you can, swap it for the correct size. It's easier, neater and it will save any confusion in the future.

mapj1 · 11 Jan 2005

Its fine, apart from the extra stiffness and trouble, as noted.
It is just possible that your installer needed 2.5mm to meet the voltage droop requirement, but only if you have a very large rambling property. Its far more likely this was all that was in the van at the time and the last light on the chain was wired on a friday.
If, given the cable size, there is not enough room in the rose, you can use a junction box, but mount it firmly to the rafters in a place where it is not going to be damaged because it wasn't seen, and where it can be inspected later if need be with minimum hassles. (if the loft is to be boarded, it might be better on a vertical prop post, depends on your roof.)
I'd leave the existing cables well alone if there is nothing wrong with them.
regards,
M.

paddy1 · 11 Jan 2005

When i attached the new rose and the new switch in the loop using the 2.5mm cable and put the mains back on, everything was fine until i switched on the new light in the roof space, at this stage the fuse in the cosumer unit for this circuit blew.
Is this because of my wiring rather than using the 2.5 mm cable instead of 1 or 1.5.
There are only 5 lights currently on this circuit and this would be number 6 so I couldnt imagine the circuit being overloaded.

Thanks

mapj1 · 11 Jan 2005

Don't worry,
It is absolutely nothing to do with the thickness of the cable. How you have connected to it however, quite possibly - have you put the new switch in parallel with the light instead of in series? see the "for reference section" and double check (if you have an assistant, get them to double check - like proof-reading its far easier to see the rrors of others).
Or is the new light itself miswired?
-if the fuse goes bang when you operate the switch, its because a dead short is being presented instead of the proper lamp load.
regards,
M

paddy1 · 11 Jan 2005

Not sure what you mean by in parallel or in series.
I have a cable going direct from the one way switch with one wire feeding into the two block terminal beside the brown wire from the pendant on the ceilin rose and the other wire going to the centre spot of the three block terminal in the middle of the ceiling rose.

plugwash · 11 Jan 2005

and to which blocks does the mains come in?

if all else fails draw a diagram of what you have done and upload it somewhere.

paddy1 · 11 Jan 2005

the feed in from the previous rose has the black wire going to the 2nd position in the first terminal block which has the blue neutral wire from the pendant. The red feed from the previous rose is going to the first position in the middle terminal block.

how does that sound?

Lectrician · 11 Jan 2005

Sounds like your new switch or new rose is wired incorrectly - describe that

plugwash · 11 Jan 2005

it sounds right.

i think at this stage the best bet if for you to draw a diagram. If that looks right then we start to look at possibilities other than miswiring.

paddy1 · 12 Jan 2005

everything was wired correctly - and silly me thinking that i couldn't possibly make a mistake wiring a switch - must have been asleep when i did it - Had the load and the neutral going to the L1 and L2 position on the switch and nothing going to the Load. Doh... too busy thinking it was something more serious than bothering to look at the most simple thing.

Thanks for all your help.

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cable size

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