Cable size for halogen lamps

[Mr Fizzion]

Why do the instructions on wiring a box of mains halogen lamps state that the minimum cable size is 1.0 sq mm, when the lamps are only a total of 250 watts (5 x 50w)?

Since the current will be around 1 amp, I would have thought I could use 0.5 sq mm cable?

Mr F.

[Christian McArdle]

1.0mm is the minimum generally available for fixed wiring installation.

Also, halogen lighting can have a massive inrush current, so a bit of extra metal can help.

Christian.

[Mr Fizzion]

Hmm, I can get this in 0.75mm:

don't seem to sell twin cable (without earth) in any larger guage.

Any other good cable suppliers?

Mr F.

[Christian McArdle]

should come with a suitable flex ready attached. Which is it?

Christian.

[Mr Fizzion]

It's a pack of 5 halogen downlighters to be permanently installed in the ceiling void. They will be replacing a single standard tungsten filament lamp. There is no cabling in the pack.

Mr F.

[Christian McArdle]

Then you must use a minimum 1.0mm PVC cabling. The link you posted was for flex, which must not be used in this application, particularly as the fitting manufacturer explicitly stated 1mm cable as a minimum.

Try:

't forget to buy coloured sleeving when connecting to a non-colour harmonised installation. You do need to wire up the earths, even if the fittings don't actually use them. Just bend back and insulate the unwanted earth at the fittings, whilst ensuring they're all connected properly where they join the existing installation. Any replacement fittings may well require the earth.

Christian.

[Mr Fizzion]

OK, thanks for all the advice.

Is it necessary right now to buy sleeving for connecting to non-harmonised installations? I saw a list of dates somewhere for when these things become mandatory and I also saw some warning stickers you could affix at the boundary of "old to new" installations warning about the colour changes.

Also are fireproof covers mandatory for downlights installed in a plasterboard ceiling?

TIA

Mr F.

[conductivity]

You also have to consider volt drop - dependant upon the length o cable. This can affect the current rating of the cable. You also need t consider the mechanical strenght of the cable for safety reasons. thank

-- conductivity

[Christian McArdle]

Yes, if the new cable is in the new colours.

It depends what is above. If the space is insulated, then, yes you need the fire covers. The side effect of these is that the lamps may overheat, leading to premature failure.

Christian.

[Christian McArdle]

Volt drop on mains halogens will be negligible in a domestic situation. It's a different matter for LV.

Christian.

[Mr Fizzion]

Yes, less than 0.1 volt per amp per metre of 0.5 sq mm copper conductor. 5 amps, which is typical of an LV transformer set up will give you 1/2 a volt per metre with the same wire. That's a bit too much! :-)

Mr F.