Smoke alarm wiring question

[bmoon]

Assuming that the cable to the alarm is appropriate (similar to that in the lighting circuit), you would not need a fused connection unit to connect it to the lighting circuit. Just a double-pole switch (easily found) would be adequate.

Yes the cable is the same as used in other circuits. Would a 13amp switch suffice?

It's obviously your decision but, as I said before a switch in the loft is hardly worth having. If something goes wrong with the alarms and trips the lighting breaker (at nightime, of course!), I can't imagine it would be much fun trying to get into the loft to operate the switch so that you could get your lights back on! As Iggifer and I have said, a switch high up on a wall is not very intrusive, and ought to be easily connected to things in the loft.

I can fully understand the reasoning behind this, but I guess I have to persuade myself to make the decision.

Thanks to all you guys for your help and advice. I will carry out the work this weekend and update you on it.

 

[JohnW2]

Assuming that the cable to the alarm is appropriate (similar to that in the lighting circuit), you would not need a fused connection unit to connect it to the lighting circuit. Just a double-pole switch (easily found) would be adequate.

Yes the cable is the same as used in other circuits. Would a 13amp switch suffice?

I don't think you'll find a 13A switch. Those sold for lighting circuits are usually 10A (sometimes 6A) but are not double pole. The most common double pole switches are 20A, but there are probably 10A ones as well - either would do.

I can fully understand the reasoning behind this, but I guess I have to persuade myself to make the decision.

Yep, that's about it!

Kind Regards, John

 

[Iggifer]

could even combine

http://www.neweysonline.co.uk/mk-el...-module/1050079302/ProductInformation.raction

http://www.neweysonline.co.uk/mk-el...le-gang/1000006883/ProductInformation.raction

http://www.neweysonline.co.uk/mk-el...ockouts/1000006893/ProductInformation.raction

http://www.neweysonline.co.uk/mk-el...way-20a/1000007010/ProductInformation.raction

Didn't even realise they did architrave grid plates. Like it.

 

[JohnW2]

could even combine
http://www.neweysonline.co.uk/mk-el...-module/1050079302/ProductInformation.raction
http://www.neweysonline.co.uk/mk-el...le-gang/1000006883/ProductInformation.raction
http://www.neweysonline.co.uk/mk-el...ockouts/1000006893/ProductInformation.raction
http://www.neweysonline.co.uk/mk-el...way-20a/1000007010/ProductInformation.raction
Didn't even realise they did architrave grid plates. Like it.

Yes, they are cute. He could do that (particularly if he liked the aesthetics), but it's an incredibly expensive way of getting a 20A DP switch! I also think that, particularly for a DIYer, wiring a grid switch in an architrave box might not be regarded as all that easy.

Kind Regards, John

 

[bmoon]

could even combine
http://www.neweysonline.co.uk/mk-el...-module/1050079302/ProductInformation.raction
http://www.neweysonline.co.uk/mk-el...le-gang/1000006883/ProductInformation.raction
http://www.neweysonline.co.uk/mk-el...ockouts/1000006893/ProductInformation.raction
http://www.neweysonline.co.uk/mk-el...way-20a/1000007010/ProductInformation.raction
Didn't even realise they did architrave grid plates. Like it.

Yes, they are cute. He could do that (particularly if he liked the aesthetics), but it's an incredibly expensive way of getting a 20A DP switch! I also think that, particularly for a DIYer, wiring a grid switch in an architrave box might not be regarded as all that easy.

Kind Regards, John

Thanks Iggifer I can imagine it will look very nice on the wall.
On the other hand, I don't dislike aesthetics but I am more of a simplist . So better for me to do things in a simple way with minimal chance of going wrong.

 

[PrenticeBoyofDerry]

You don't actually require a switch or isolator to comply to 1.19. You only need a means to isolate the detector/alarm.
This could be as simple as being able to remove the alarm by sliding of the base.

 

[JohnW2]

You don't actually require a switch or isolator to comply to 1.19. You only need a means to isolate the detector/alarm. This could be as simple as being able to remove the alarm by sliding of the base.

Now you tell us Maybe you should have mentioned that when you first mentioned 1.19 of the AD!

However, what 1.19 says is "There should be a means of isolating power to the smoke alarms without isolating the lighting." Are you sure that 'sliding off the base' would qualify as that. Are they perhaps thinking of a situation in which, say, the alarm bursts into flames, or becomes mechanically damaged exposing live parts, so that isolation of power to the alarms is required?

In any event, are all alarms such that they can be safely 'slid off the base' whilst powered? A proper isolator/switch sounds like a better idea to me!

Kind Regards, John

 

[PrenticeBoyofDerry]

Maybe you should have mentioned that when you first mentioned 1.19 of the AD!

I don't recall mentioning an isolation switch was required, but forgive me if I was not more elaborate.

I agree that an isolation switch, would be a more logical/practical use, if the situation was that the unit had burst in to flames.
But as far as compliance to 1.19 is concerned, a number of manufacturers use a fixed base for the electrical connections, and the smoke or heat alarm can be readily removed by use of a tool operated release tab, etc. and this is deemed an acceptable means of isolation.

 

[Lectrician]

The BS5839 P6 used to say (not 100% sure if this is still correct) that smoke detectors fed from a dedicated circuit need not have battery backup, but if fed from a local lighting circuit they must have battery backup.

I always thought this to be backward thinking.

I lighting circuit failing will be addressed as a matter of urgency, and power restored to the alarms. I dedicated circuit failing would not be noted so quickly, and unlikely to be addressed with haste. Battery backup would surely be more preferred on the dedicated circuit rather than the lighting circuit.

In any case, these days, battery backed types are as cheap (and more available) than non battery backed types.

If you really did want to install an isolator (and personally I wouldn't), you could go for a secret-key switch, and if using a grid module to provide this (rather than say a legrand plate), you could even include a neon indicator and use a two way key switch. With the key switch OFF, the neon would be on. This was the spec on several jobs we did a while ago for em lighting test switches.

 

[bmoon]

Now it's started...

I also thought about using the sliding base as a means of isolation. But on the other hand, what if the alarm is ok but the connection INSIDE the base is faulty and causing the breaker to trip? Removing the alarm unit from the base won't isolate the circuit/problem anyway in that case.

So I will go and do it in the proper way. I now have two really basic questions:
1. Where on the lighting circuit should I get the power? Can I just drop a cable from the loft to one of the light switches to get live and neutral there?
2. What type of cable I should use?

This is the current cable used for the alarms/lighting ect:
View media item 62083
This is what I have in hand:
View media item 62084
The earth is connected to the base of the alarms but not used, so I am assuming I can use a two-core cable. But if not I will buy the correct/current type.

BTW I've found a better place for the switch though - in the cupboard (so the visible wall will not be more messy than it is now). There is already a switch in there for the emergency boiler I think, so it should be ok to add another one?

Thanks!

 

[Lectrician]

No. You cannot use two core cable. Every point in an electrical installation requires an earth, even if not used and connected to a terminal block in the back of the accessory. If you don't take an earth to it, the earth to the next smoke/heat won't be earthed.

A switch is unlikely to have a neutral.

A cable between two pendents is likely to have a perm live and a neutral. Take it to the closest pendent that has more than one set of cables.

Look at this, this is more than likely how your lights are wired.

 

[bmoon]

No. You cannot use two core cable. Every point in an electrical installation requires an earth, even if not used and connected to a terminal block in the back of the accessory. If you don't take an earth to it, the earth to the next smoke/heat won't be earthed.

A switch is unlikely to have a neutral.

A cable between two pendents is likely to have a perm live and a neutral. Take it to the closest pendent that has more than one set of cables.

Well, I am enjoying this learning process.

So this is how I would do it. Is it correct?
View media item 62088

 

[JohnW2]

Maybe you should have mentioned that when you first mentioned 1.19 of the AD!

I don't recall mentioning an isolation switch was required, but forgive me if I was not more elaborate.

No, you didn't mention an isolation switch explicitly, but when you wrote:

It is a much ignored building regulation that smoke alarms should have a means of isolation that will not effect the lighting circuit. Look at 1.19 (Page 14)

...I would strongly suspect that most people will (like me!) have thought of nothing other than an isolation switch!

I agree that an isolation switch, would be a more logical/practical use, if the situation was that the unit had burst in to flames. But as far as compliance to 1.19 is concerned, a number of manufacturers use a fixed base for the electrical connections, and the smoke or heat alarm can be readily removed by use of a tool operated release tab, etc. and this is deemed an acceptable means of isolation.

I suppose that, since 1.19 requires a means of isolation of power 'to the alarms' it depends upon what it means by 'the alarm' - does it include the base or not?

I must say that I'm inclined to agree with Lectrician that, whatever regulations of guidelines may say, the whole concept of having a means of easily 'switching off' smoke alarms (maybe unintentionally) is a bit worrying. His suggestion of a key-operated isolator would certainly help, but even that is not foolproof. Whatever is the thinking behind this 1.19, it certainly seems to work against the interests of fire safety. I confess that if I felt compelled to have some sort of 'means of isolation', I might settle for single-pole isolation and install an unswitched FCU with a 13A fuse in it.

Kind Regards, John

 

[bmoon]

I must say that I'm inclined to agree with Lectrician that, whatever regulations of guidelines may say, the whole concept of having a means of easily 'switching off' smoke alarms (maybe unintentionally) is a bit worrying.

Would the backup battery be of a bit help here? When the circuit is switched off or broken, the alarm would either continue to work on the battery, or beep when the battery is drained. Also the little green light on the alarm may help a bit I suppose.

 

[JohnW2]

Would the backup battery be of a bit help here? When the circuit is switched off or broken, the alarm would either continue to work on the battery, or beep when the battery is drained. Also the little green light on the alarm may help a bit I suppose.

Yes, of course, that's the whole point of having a back-up battery - but I would personally still prefer not to have an 'easy means' of switching off the mains power to the alarms.

Kind Regards, John