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.

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)?

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.

On Mon, 15 Aug 2005 11:32:33 +0100, "Christian McArdle"
wrote:

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)?

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.


Hmm, I can get this in 0.75mm:
http://www.screwfix.com/app/sfd/cat/...05998&id=14444

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

Any other good cable suppliers?

Mr F.

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

Hmm, I can get this in 0.75mm:
http://www.screwfix.com/app/sfd/cat/...05998&id=14444

That's flex and should not be used in fixed wiring. A portable appliance
should come with a suitable flex ready attached. Which is it?

Christian.

On Mon, 15 Aug 2005 13:40:55 +0100, "Christian McArdle"
wrote:

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

Hmm, I can get this in 0.75mm:
http://www.screwfix.com/app/sfd/cat/...05998&id=14444

That's flex and should not be used in fixed wiring. A portable appliance
should come with a suitable flex ready attached. Which is it?


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.

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.

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:

http://www.screwfix.com/app/sfd/cat/...14670&id=74536

Don'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.

On Mon, 15 Aug 2005 15:08:04 +0100, "Christian McArdle"
wrote:

Don'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.


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.

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

Is it necessary right now to buy sleeving for connecting to
non-harmonised installations?

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

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

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.

You also have to consider volt drop - dependant upon the length of
cable.

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

Christian.

On Mon, 15 Aug 2005 18:02:40 +0100, "Christian McArdle"
wrote:

You also have to consider volt drop - dependant upon the length of
cable.

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

Christian.

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.