Installing LV downlights

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I'm thinking of installing low voltage downlights in my L-shaped kitchen. I current have 3 pendants, one in each "zone" of the L. 2 zones are in the single storey extension, the third is directly below my bathroom. I was wondering what access is needed to install these:

- Do I need access from above, or is it possible to make the holes and thread the cabling through the cavity using a coat hangar or similar?
- Is it OK to connect the transformer up to the original wiring then stuff it in the old pendant hole and make good, or is "maintenance" access needed?
 
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Access can be from above or below, but if your extension has a flat roof, the only way will be from below.

It may be possible to get cables between the holes, or you may need to remove sections of the ceiling to drill through the joists or move whatever else is in the way. Note that you will need to clear insulation away from where the lights are fitted to avoid overheating, however if you remove all of the depth of insulation this will make that area of the ceiling very cold, and probably not comply with building regulations.

Normally you have one transformer for each light, and they are small enough to pass through the same holes that the lights fit into, so future maintenance is not an issue. Same applies to the junction boxes which will be required.

Lights with transformers operate at 12 volts, which is ELV.
LV ones are 230 volts, and don't have transformers.
 
FYI:
The IEC definitions of voltage bands are:
  • Extra Low Voltage: AC below 50V and DC below 120V
  • Low Voltage: 50 - 1000V AC or 120 - 1500V DC
  • Medium voltage: 1kV - 35kV
  • High voltage: 35kV - 230kV
  • Extra-high voltage: >230kV
This is not some pedantic technical point - if you start getting involved in doing your own electrical work, and start learning about regulations etc you'll come across references to "Low voltage", and it'll be no good you thinking that that means 12V...




Anyway.

If you just replace the 3 pendants with 3 downlighters the illumination will be terrible, because you'll be using lights which were not originally designed to light up rooms. They are often called spotlights, with good reason - they give out a narrow beam of light which is designed to highlight individual items or small areas. They were originally designed for retail display lighting, and are s***e at doing anything else.

If you install lots more to get around that problem then your electricity bill will be horrendous, and you'll still have brighter/dimmer areas where the beams overlap.

And in England or Wales it would be notifiable, which raises the problem of what do you do about the fact that you'd be in contravention of Part L.

With no access from above you'll also have another contravention of Part L because of the reduction in insulation, and as it's in a kitchen you may create a Part C contravention.

Depending on the depth of the roof, you may not have enough clearance for the lights, and if solid insulation has been installed you'll need to initially make large holes to get rid of enough, and then make good. On the ceiling around the lights you may then get condensation and, over time, dirty marks caused by convection currents.

Cable runs will be compromised by where the joists are and where they run, and again solid insulation may make installing extra cabling very difficult - removing and replacing the ceiling may be the only option. ELV currents are quite high so you'll need to watch the cable sizes carefully given de-rating factors caused by insulation and for voltage drop.

http://www.tlc-direct.co.uk/Book/4.3.1.htm

http://www.tlc-direct.co.uk/Technical/Lighting/VoltageDrop.html


Any screwed cable joints, e.g. junction boxes, transformer connections need to be accessible for maintenance and inspection, and transformers can be unreliable anyway.


So in short it could be a difficult job, it could cause you legal problems, it will be expensive to run, and the results will be s***e.
 
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....and...

Your existing pendants will be sited on joists or other supporting woodwork. You cannot put downlights in those positions.

In these situations, my experience has been that it is better to rip the ceiling down and do it properly.

Its cheaper to do that if you count the time taken to stitch cable across ceilings, trying to avoid joists, finding there are pipes etc in the way.

Also bear in mind that the cable should be clipped to the joists, not just draped above the plasterboard.
 
Thanks for the comprehensive and information replies. I did a similar job once before when installing a suspended ceiling, but hadn't thought of all the added difficulties of the new environment. For the record I wasn't planning a 1-to-1 swap with the existing pendants - I was intending to drive 4x downlights off a single transformer connected to the original supply.

Anyway, banallsheds' comments re. legality of said job have made me think again, though I must admit that I actually like the lighting effect that downlights give in a kitchen.
 
I must admit that I actually like the lighting effect that downlights give in a kitchen.
The fact that you need 4 x as many lights tells you nothing about their fundamental unsuitability for actually lighting up a room?
 
Also bear in mind that the cable should be clipped to the joists, not just draped above the plasterboard.

"SHOULD"

Does anyone ever do this these days?

I mean, I lift boards in my house and some of the original VIR wiring is still in place (though not in use), and it is clipped beautifully along joists. The more recent additions (done by a pro 20 years ago) are just draped everywhere. :rolleyes:
 
So if you run a cable from one side of the house to the other, your going to pull up every 5th or so board just to clip the cable? Me thinks not :)
 

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