Downlighters into Plywood??


Postby chrisjones » Sun Jul 20, 2008 12:42 pm

Hi

My builder has built some "light boards" (3 in total) for our hall as we live in a coverted house so cannot install downlghts into the ceiling directly. There are 6-8 Mini Halogen Downlights (from B&Q) per board but I have just noticed that they are not Fire Rated although, they are Low Voltage (20 Watt). He's also only left about 2"-3" clearance between the fitting and the ceiling.

As such, do I need to worry or do I need to look to change the downlights for Fire Rated ones...or should I foget the boards altogther!?!? I have read that Fire Rated are ok for wood but have also read the opposite (!) so am really looking for what the regs actually stipulate!

Any advice would be greatly apprciated!

Thanks in advance.
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Postby ericmark » Mon Jul 21, 2008 8:38 am

I will assume in order to be multi lingual we have an array of signs used to tell us about our lamps Table 55.2 in BS 7671:2008 lists these. The one with an F in a triangle with apex to bottom means “Luminaire suitable for direct mounting on normally flammable surfaces” the same with cross through it means “Luminaire suitable for direct mounting on non-combustible surfaces only” and an F in a triangle with apex to bottom with line across top means “Luminaire suitable for mounting in/on normally flammable surfaces where a thermal insulating material may cover the luminaire NOTE: The marking of the symbol, corresponding to IP numbers is optional”. Luminaires marked “with a D in the triangle” are designed to provide limited surface temperature.
422.3.1 Except for equipment for which an appropriate product standard specifies requirements, a luminaire shall be kept at an adequate distance from Combustible materials. Unless otherwise recommended by the manufacturer, a small spotlight or projector shall he installed at the following minimum distance from combustible materials:
(i) Rating up to 100 W 0.5 m
(ii) Over 100 and up to 300 W 0.8 m
(iii) Over 300 and up to 500 W 1.0 m
NOTE: A luminaire with a lamp that could eject flammable materials in case of failure should be constructed with a safety protective shield for the lamp in accordance with the manufacturer's instructions.

For the above regulation I think it refers to what it is pointed at but it does not say that and some lamps with special reflecting surfaces called Diachronic allow heat to pass through reflector and only reflect the light.

I have a 20 watt 2D down lighter in one of the bed rooms quite cool a little too bright about 9 inches diameter and has been mounted in wood for years but other bedroom has GU10 bulbs and one is 11 watt cold cathode which is not really bright enough on its own although I can reach up and move it’s direction without burning myself and the other 50 watt tungsten which is only as bright as the 2D lamp and is very hot and I have burn myself on it. So to give a general answer is impossible.

GU10 lamps and also the 12 volt versions seem to work well when in pods but sunk in the ceiling they seem to require well over the wattage of standard pedant lamps I fitted 10 x 10 watt lamps in one house the owner insisted and it looked more like a planetarium. Yet same wattage in pendent lamp was ample with single 100 watt bulb. The larger 2D type do seem to work well but need the ceiling height which does not tend to be there on most domestic premises. Seems nothing can really beat the pendent lamp which reflects most the light off the white ceiling giving general light without too much shadow unless you use florescent tube lighting.

I think you will gather as an electrician I don’t like down lighters and with tungsten bulbs being slowly being withdrawn from service I would never recommend tungsten halogen down lighters.

All best Eric
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Postby TOPSPARK » Sun Jul 27, 2008 10:40 pm

Hi chris
the distance between the plywood boards and the existing ceiling is nowhere near enough for the heat given off to dissipate.ericmark has given you the technical information. I will give you some plain info always use fire rated downlighters and form the top of the fitting that is in the void have at least a 200mm gap for the heat to dissipate and go through the false ceiling.The diy lights from B&Q look good but are all open and offer no protcetion if false ceiling is insulated. always goto a reputable wholesalers and seek their advice and view their products or if unsure consult a qualified electrician
all the best
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