Is this beyond the scope of your average DIY'er? Reason for asking is
that I will be channel lining my kitchen ceiling, so should be easy to
run any neccessary wiring as I go along. Or is this a job for a proper
sparky? Downlighters are 240v, probably 35W or 50W lamps. Should be no
heat issues as plenty of space. Any advice appreciated.

"Mitch" wrote
| Is this beyond the scope of your average DIY'er? Reason for asking
| is that I will be channel lining my kitchen ceiling, so should be
| easy to run any neccessary wiring as I go along. Or is this a job
| for a proper sparky? Downlighters are 240v, probably 35W or 50W
| lamps. Should be no heat issues as plenty of space. Any advice
| appreciated.

If this is a ceiling rose you should replace it with a proper junction box.

With regards to cable/circuit ratings, under the regulations *each*
downlighter will be assumed to be 100W minimum (or actual loading if
greater) and you should check that you will not be overloading the existing
circuit.

The general consensus is that low voltage lights are better than the mains
halogens, and if you put 2 x 200W transformers in (with 4 lights on each)
the assessed load would be kinder. Also you can switch them separately.

Owain

In uk.d-i-y, Owain wrote:

With regards to cable/circuit ratings, under the regulations *each*
downlighter will be assumed to be 100W minimum (or actual loading if
greater) and you should check that you will not be overloading the existing
circuit.

I'm pretty sure this is not the case: the intent of the Regs would
surely be to say "anywhere a mumpty might put in an ordinary bulb, you
have to allow for mumpty favouring 100W bulbs", which is fair enough.
But if you have a lighting point whch takes non-ordinary-bulbs, you
surely assess the load based on - at very worst - the biggest-load
bulb available for that fitting; so, 20W for diddy-capsule halogens,
50W for bigger-size reflector ones, 11W for PL11D flourescents, and
so on. No? Likewise if the transformer you fit limits the load (so
that even if mumpty replaces 20W bulbs with 50W ones there won't
be a sustained overload, as the transformer will shut down or have its
fuses blow), it's reasonable to rate the load according to the
maximum the transformer will draw, not some mythical 100W-per-ligthing-point...

But what do I know? I've never made the time to read the Regs themselves,
as they seem to be statements of abstract principle leavened with
detailed engineering calculations to allow a tight balance between
safety and economy across a huge variety of installations. For d-i-y
work, the On-Site guide is as Official as I've ever wanted to get,
supplemented by the "working domestic electrician" books like the
venerable Stumbles.

Stefek

In uk.d-i-y, wrote:

I'm pretty sure this is not the case: the intent of the Regs would
surely be to say "anywhere a mumpty might put in an ordinary bulb, you
have to allow for mumpty favouring 100W bulbs", which is fair enough.

Ah, the sweet sweet taste of a foot in the mouth... having posted, I
realise that the OP said "downlighter", and it was my own imagination
that imagines the qualifier "12V halogen". So the little rant about
sizing-by-max-available-bulb was gloriously irrelevant; and in any
case Owain's suggestion that 12V fittings with multiple switches
(2 strings of 4, or 3+3+2) is in any case a Good One.

Apolopogies - Stefek

Stefek Zaba wrote
| With regards to cable/circuit ratings, under the regulations *each*
| downlighter will be assumed to be 100W minimum (or actual loading
| if greater) and you should check that you will not be overloading
| the existing circuit.
| I'm pretty sure this is not the case: the intent of the Regs would
| surely be to say "anywhere a mumpty might put in an ordinary bulb, you
| have to allow for mumpty favouring 100W bulbs", which is fair enough.
| But if you have a lighting point whch takes non-ordinary-bulbs, you
| surely assess the load based on - at very worst - the biggest-load
| bulb available for that fitting; so, 20W for diddy-capsule halogens,
| 50W for bigger-size reflector ones, 11W for PL11D flourescents, and
| so on. No?

I think not (for mains fittings), because there is always the possibility
that someone replaces the low-energy Part L compliant fitting with a
standard bayonet battenholder and sticks in a 150W GLS lamp.

| Likewise if the transformer you fit limits the load (so
| that even if mumpty replaces 20W bulbs with 50W ones there won't
| be a sustained overload, as the transformer will shut down or have
| its fuses blow), it's reasonable to rate the load according to the
| maximum the transformer will draw, not some mythical 100W-per-
| ligthing-point...

In a transformer case I agree and would regard the transformer as being the
'point' rather than the number of lamps it supplies, as the transformer
signifies the end of the mains wiring. So a transformer feeding 6 x 50W
lamps is considered to be a 300W point load rather than 600W across multiple
points.

You can stop sucking your verucca now :-)

Owain