Mains smoke and heat detectors

[eveares]

I'm a bit late in this conversation, but...

Also, CO detectors if interlinked with smoke detection will require an alarm controller to indicate cause of alarm (smoke/CO).

But how about a combined mains smoke and CO detector, one that has two different sounds for each type of alarm?

52.3 is nonsense. It is not possible to comply with regulations which are nonsense. 52.3 has to be ignored.

I like your thinking...

Well 3A mcbs are not a common device

3A or 6A MCB regardless, both 1mm² and 1.5mm² are usually suitable in most domestic situations.

You could, of course, use flexible cable in which case it is allowed to use a smaller csa unless you consider 'sheathed or unsheathed flexible cable' is also a 'sheathed or unsheathed cable' in which case you can't.

I think on that one we can agree that "sheathed or unsheathed cable" is talking about non flexible cables. Either way I agree that it is very silly and utter nonsense that you can use 1.0mm² Flex but not 1.0mm twin and earth!


Also what happens if you had a lighting circuit with smoke alarms wired in 1.0mm² T&E and then you later removed all the lights from the circuit. Also has anyone considered the possibility of that if you add smoke alarms to a lighting circuit, that it may technically become a "power circuit" and thus 1.5mm² is required if you use T&E?

 

[PBC_1966]

52.3 is nonsense. It is not possible to comply with regulations which are nonsense. 52.3 has to be ignored.

It is perfectly possible to comply. What is "nonsense" about it?

This restriction is a completely new one on me which I'd not heard of before reading this thread, but based on the table which has been quoted, plus the additional statements that BS7671 doesn't specifically define what is mean by "lighting circuit" or "power circuit," how is one supposed to interpret what is actually meant by those terms?

To me, in the absence of some specific definition for a specific purpose, "power circuit" means any circuit intended to deliver power to some sort of load. That would include lighting, which means that "lighting circuit" is just a subset of "power circuit." Obviously to read that table and say that a lighting circuit needs only 1.0 sq. mm cable but then say, "Ah, but it's a power circuit too, so it needs to be 1.5 sq. mm" would be nonsensical in the extreme, as if that was the intent they would have just listed 1.5 sq. mm as the minimum for everything (signaling, telecoms etc. excepted) and wouldn't be trying to make some sort of distinction between "lighting" and "power" circuits.

The only logical deduction to make is that they meant "power circuit" to mean something which delivers power but which is not a "lighting circuit." So what does "lighting circuit" mean? I think we'd all agree that if the circuit supplies nothing but lights it must be a lighting circuit, and if it supplies no lights it can't be a lighting circuit. But what about all those in-between cases already mentioned?

Does it have to supply only lights to be lighting circuit, or does it become a lighting circuit if, along with other loads, it supplies any light?

But even if we limit it to the obvious cases of only lights or no lights, it's surely nonsense to say that you can supply a kilowatt of lighting on a circuit wired in 1.0 sq. mm T&E, but that if you wanted a dedicated circuit for a couple of hundred watts' worth of fans and smoke detectors it has to be 1.5 sq. mm?

 

[EFLImpudence]

Unless, of course, you use flexible cable under the "any other application" clause when the required minimum csa is half that.

 

[PBC_1966]

Unless, of course, you use flexible cable under the "any other application" clause when the required minimum csa is half that.

Which makes perfect sense, of course.......

 

[JohnW2]

Unless, of course, you use flexible cable under the "any other application" clause when the required minimum csa is half that.

Quite - as has been said, the whole thing is sheer nonsense!

Kind Regards, John

 

[ban-all-sheds]

It is perfectly possible to comply. What is "nonsense" about it?

Can you tell me how I can distinguish between a power circuit and a non-power circuit?

 

[ban-all-sheds]

The only logical deduction to make is that they meant "power circuit" to mean something which delivers power but which is not a "lighting circuit." So what does "lighting circuit" mean? I think we'd all agree that if the circuit supplies nothing but lights it must be a lighting circuit, and if it supplies no lights it can't be a lighting circuit. But what about all those in-between cases already mentioned?

What about circuits which are both?

All my lighting circuits deliver power - I find that that is the best way to ensure that the lights light up.

 

[PBC_1966]

Of course - As I said earlier:

]one could ask how it's possible to get lights to work without supplying them with power......

 

[Risteard]

Does it have to supply only lights to be lighting circuit, or does it become a lighting circuit if, along with other loads, it supplies any light?

I would say any circuit substantially for lighting would be a lighting circuit, and therefore there is no problem supplying extractor fans or smoke detectors etc. from a lighting circuit (and therefore using 1mm^2 cable).

However, in the absense of a definition, this is merely my opinion.

 

[PBC_1966]

I would say any circuit substantially for lighting would be a lighting circuit

Given the absence of any other definition that seems as reasonable an interpretation as any. But it would mean that if you had a circuit with, say, 10 lighting points and just a couple of fans and smoke detectors, you could wire the whole lot in 1.0 sq. mm. But if the same MCB supplied a dozen fans, a couple of smoke detectors, and only one light (or indeed none at all) the whole lot would need to be done in 1.5 sq. mm, even though the total load could well be substantially less than in the former case. It makes no technical sense whatsoever.

 

[eveares]

Unless, of course, you use flexible cable under the "any other application" clause when the required minimum csa is half that.

And that has to be the biggest blunder of it all, I am sure BAS would agree.

 

[foxhole]

THANKS, started to read the many replies but beginning to give up the will to live.
So can I install them off the existing lighting circuit [6amp] with 1.5 twin and earth?

 

[RF Lighting]

1.0mm² twin and earth or three core and earth as required would be the ideal cable to use.

 

[stillp]

Unless, of course, you use flexible cable under the "any other application" clause when the required minimum csa is half that.

And that has to be the biggest blunder of it all, I am sure BAS would agree.

Not really. The minimum CSA is not only for reasons of current-carrying capacity, but also for mechanical strength. I think the table is a selection from IEC 60364-5-52, but I'll try to check later.

 

[stillp]

It is perfectly possible to comply. What is "nonsense" about it?

Can you tell me how I can distinguish between a power circuit and a non-power circuit?

By using your competence to design circuits and performing a judgement.