Kitchen cupboard downlights - couple of questions


Postby chrisparis » Sat Feb 25, 2012 1:34 pm

Hello All

I have bought some downlights to go under my kitchen cupboards.

They are two sets of three lights, each set has its own transformer and a plug.

I want to wire the two sets into a fcu Does anyone see a problem with that? Would a 13amp fused fcu do for that. The instructions say the transformer ought to be protected by a 5amp fuse, but then it shows that the plug has a 3 amp fuse in it ! What is going on there?

I want to hard wire both the sets into one switched and fused fcu.
chrisparis
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Postby ericmark » Mon Feb 27, 2012 4:21 am

Due to Part P saying a kitchen is a special area fixing the lights technically needs you to first inform the LABC and pay their fee. Which will cost more than getting an electrician who is a scheme member to do the job for you.

However if you did want to DIY and pay the LABC then yes you could use a FCU. Although in the UK we can get 1, 2, 3, 5, 7, 10, and 13 amp fuses for our plugs the fuse in the plug is only to protect the cable not the appliance as the same appliance could be used in rest of Europe where they don't have fused plugs. So any appliance protection should be in the appliance its self. As a result we have two preferred sizes of fuse the 3A and 13A which are far more available than the other sizes.

Our ceiling roses are rated at 5 or 6 amp and so in the main most lighting circuits will have either a 5A fuse or 6A MCB. The humble bulb holder is rated at 2A but there is suppose to be a fuse built into the bulb so this is permitted.

This will explain why you see both 3A and 5A being referred to.

Anything which is installed rather than just plugged in and used can have instructions as to what protection is required. So a hob manufacturer can require you to fuse down for example fitting a 3A fuse in the supply to a gas hob igniter.

So as to fuse size the inverter (transformer) may have an in-rush when switched on which may mean a larger fuse then calculated may be required. But if for example you had 6 x 50W lamps then 300/230 = 1.3A so the 3A fuse should be ample. If it blows then no real problem going up to 5A as in-rush could blow a 3A fuse but unlikely. It is likely that what you call a transformer is in fact an inverter and will not have that much of an in-rush to charge the capacitors so in real terms there is unlikely to be a problem running both units from one 3A fuse.

Remember if not already protected you will to comply with BS7671:2008 need RCD protection for any new outlet. So if you are going down the LABC route you may need to use a RCD FCU to comply with the regulations in order for the LABC to issue the completion certificate. Some how though I can't see you paying the LABC their £100 plus fee?
ericmark
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