Number of luminaires on a lighting circuit – new house

Dave Stevenson:

Zoomup:

Why do motor cars have dual breaking systems and a hand brake as well, the Americans call the latter an emergency brake.


Z.

Because there would be an immediate danger to life if the brake circuit failed - I would suggest that's hardly the same as a lighting circuit going out

"Circuits" plural! Time was we only had brakes on the back axle and rods or cables to work them. Nowadays, I think that they are fly-by-wire, which I find a little disconcerting.


I wouldn't fancy driving at night if the fuse went and I couldn't see a thing. ?


Same really at night when you cannot be bothered to switch on the landing light when answering the call of nature. People have been known to fall down the stairs as a result!

davezawadi (David Stone):

I know you are always very aware of fire Z, but this is ridiculous. You need to realise that LED power supplies are inherently fire resistant in several ways. The components used are very small, they are often the fastest fuses known to man, and cannot dissipate many watts without vapourising. To start a fire one needs significant power dissipation but this is close to impossible with these items, at perhaps 5W maximum, and if anything goes short circuit (which it almost certainly will) the current will trip the circuit OPD. 

 A 16 Amp M.C.B. needs many Amps  trip it off. Especially a C16 type on a short circuit. So, do L.E.D. luminaries have internal fuses or do they just rely upon their tiny electronic parts exploding to clear a fault? I don't really like the thought of that happening. I know that the old wound toroidal lighting transformers had an electrical fuse, and a thermal fuse embedded into the windings for safety.


Years ago, even electric clock points has a cartridge fuse, normally 1 Amp rated, for an electric clock that posed little fire risk or overload risk. Also Friedland bell transformers had internal fusing to supply just E.L.V. door bells. 


Z.

Zoomup:

davezawadi (David Stone):

I know you are always very aware of fire Z, but this is ridiculous. You need to realise that LED power supplies are inherently fire resistant in several ways. The components used are very small, they are often the fastest fuses known to man, and cannot dissipate many watts without vapourising. To start a fire one needs significant power dissipation but this is close to impossible with these items, at perhaps 5W maximum, and if anything goes short circuit (which it almost certainly will) the current will trip the circuit OPD. 

 A 16 Amp M.C.B. needs many Amps  trip it off. Especially a C16 type on a short circuit. So, do L.E.D. luminaries have internal fuses or do they just rely upon their tiny electronic parts exploding to clear a fault? I don't really like the thought of that happening. I know that the old wound toroidal lighting transformers had an electrical fuse, and a thermal fuse embedded into the windings for safety.


Years ago, even electric clock points has a cartridge fuse, normally 1 Amp rated, for an electric clock that posed little fire risk or overload risk. Also Friedland bell transformers had internal fusing to supply just E.L.V. door bells. 


Z.

Update. After just carrying out a kitchen table experiment I have found out that the G.U.10 L.E.D. lamps that I use do not burn. The lamps are encapsulated in a white "plastic" and have a clear lens.  I applied a cigarette lighter flame to the white plastic body and the plastic did not burn. No smoke was evident as well. It did become soft though as I found out when I burnt my finger tip when pushing on it. So the lamps may contain exploding components during an internal fault. I wonder how loud the bang will be? If the lamp was subjected to continued heat it may soften, melt and fall apart and bits fall out onto the floor.


Z.

Dave Stevenson:


I think that the requirement for fireproof downlighters or fire hoods is driven not so much by the risk of the luminaire catching fire, it is driven by the need to protect the integrity of the ceiling, or rather, the floor above it, where there is a "habitable space" above the room, i.e., to maintain the fire rating of the ceiling. Where there is no habitable space above, neither are mandated. The floor/ceiling construction in modern homes is scary! - Do a search for photos of engineered joists after a fire - you might get a shock - I did! 


I think in response to these modern construction methods, the Technical Handbook that support Scottish building regulations now require fire protection for "elements of structure", i.e., the floor joists. If, for example, the fire protection (plasterboard) is applied to the bottom joist flange, then any ceiling below them need not have a fire rating, hence fireproof downlighters or fire hoods are not required. Most new builds won't have that void space, mine does. (There may be a requirement for fire detection in the void space, but that is under discussion with Building Control at the moment) 

Wot, this sort of consideration?

The NHBC burns a hole in fire rated downlight certification with i joists - Bing video


Z.

Dave Stevenson:

I think that the requirement for fireproof downlighters or fire hoods is driven not so much by the risk of the luminaire catching fire, it is driven by the need to protect the integrity of the ceiling, or rather, the floor above it ...

I thought about that. It explains why some luminaires have intumescent seals around the flange, but not the hoods as such. IMHO, the reason for putting a hood over a luminaire is also about giving it space to warm up. I prefer the sort of luminaire which specifies that it may be covered directly by (loft) insulation, but even then in my own house, I would want to install some sort of batten to keep the insulation off the luminaire.


What is a little odd is that such luminaires still specify a minimum distance from joists. That is a real PITA when you have spent time working out the positions of luminaires only to find that a joist is in the way.

Chris Pearson:

I have lived here for 24 years and never had to reset an MCB.

Perhaps they are suffering from sticktion Chris.


Z.

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Chris Pearson:

I have lived here for 24 years and never had to reset an MCB.

Perhaps they are suffering from sticktion Chris.

No, I can turn them off and on for isolation; but if this thread is anything to go by, there may be nothing inside. ?