Smoke alarm wiring question

[bmoon]

Hi,

This is my first post, greetings to everyone.

We have two smoke alarms in our house, one EI150 without battery, the other EI156 with battery. Some months ago the EI156 started to beep so I just disconnected it. Now we think it is important to have working smoke alarms so we try to connect it back. But we just found that the there is no electricity on the wires to the connectors of the alarms at all.

I've done some basic checks using a multimeter and a voltage test screwdriver. The breaker box seems fine - there is power on the output wire from the breaker for smoke alarms. So it looks like the wire between the distribution box and the first alarm is damaged. Two years ago we had to replace a piece of drywall in our family bathroom and the wire might have been damaged then, though I did notice the wires in the wall and paid extra attention.

The wire goes from the distribution box to the loft first, so I think it will be impossible to pull through a new cable without tearing the walls and floors open. Therefore I am considering two options:
1. Connect the alarm wire to one of the lighting wires in the loft (such as the one for the loft light) using a junction box, so they share a same breaker.
2. Replace the alarms with some battery-powered ones.

In both cases the faulty wire will be disconnected from the distribution box.

Option-1 is obviously cheaper and simpler. But my question is, is it against any domestic wiring regs or building regs? Would it invalidate our home insurance? (of course without a working alarm our insurance is invalid anyway).

Thanks for your help!

 

[Iggifer]

Option 1 is preferable, although you should have mains+battery smokes, not just mains.

It's accepted to take the supply from a nearby lighting circuit on the thinking, you will notice if the cct isn't working and something will be done about it, unlike your current smokes setup.

 

[PrenticeBoyofDerry]

It is the norm to use a lighting circuit as a supply for smoke alarms but there should be a means of isolating the alarm circuit without power-loss to the lighting circuit (often forgotten about).
I would firstly though go through the correct test procedures on the existing circuit to find where problem lies.
Continuity tests between "line-CPC", "line-neutral" and "neutral-CPC", should help diagnose any broken/damaged conductors.
It may well be that you have a loose connection or insulation trapped at terminals within CU.

 

[burntwire]

Have you checked the blue/black neutral wire that is associated with this circuit is connected? it may of snapped/ come loose, your testing screwdriver will only tell you if the red/brown wire is live, maybe check also cpc(green/yellow) to live at fitting if this shows 230 as if neutral fault and you test neutral - live, it will show as no volts

 

[bmoon]

Many thanks to you guys for your replies. I am glad to hear that option1 is feasible. Meanwhile based on your replies I do sense there is a lot I can do before carrying out the plan.

Iggifer, one of the two alarms has backup battery, so I am thinking this should be sufficient.

PrenticeBoyofDerry and burntwire, yes I will do some more tests as you have suggested.

PrenticeBoyofDerry, could you please tell me a bit more about isolating the alarm circuit? I plan to simply use a 3-terminal junction box for the job, but it looks like I would be missing something important.

 

[Iggifer]

Iggifer, one of the two alarms has backup battery, so I am thinking this should be sufficient

Presumably they are not interlinked? Which one has the battery? I would hope upstairs, as if you had a fire downstairs (say originating at your CU) that killed the power to the house, would the one downstairs necessarily wake you up?

 

[bmoon]

Iggifer, one of the two alarms has backup battery, so I am thinking this should be sufficient

Presumably they are not interlinked? Which one has the battery? I would hope upstairs, as if you had a fire downstairs (say originating at your CU) that killed the power to the house, would the one downstairs necessarily wake you up?

Yes the one with battery is upstairs. I guess they are interlinked (both have a 'interconnection' pin on the connector and the pins appear to be connected).

 

[PrenticeBoyofDerry]

PrenticeBoyofDerry, could you please tell me a bit more about isolating the alarm circuit? I plan to simply use a 3-terminal junction box for the job, but it looks like I would be missing something important.

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)
http://www.planningportal.gov.uk/uploads/br/BR_PDF_AD_B1_2013.pdf

 

[EFLImpudence]

Look at 1.19 (Page 14)

Is that an actual regulation or another example of poor guidance?

It does seem inconsistent with another part of the paragraph.

 

[bmoon]

After some more testing of the faulty circuit, I am now certain the 'live' wire is broken between the CU and the alarm, but 'neutral' is ok. The cpc is connected to the base of the alarm but not used so it should not matter. I've disconnected the broken wire from the breaker in the CU.

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)
http://www.planningportal.gov.uk/uploads/br/BR_PDF_AD_B1_2013.pdf[/QUOTE]
I did a bit of search on this, and found that there seems to be some debating about it, such as here:
http://www.ecoc.co.uk/forums/forum/...= 39935&STARTPAGE=1&FTVAR_FORUMVIEWTMP=Linear

Anyway, lets not start another debate about this here. Whether it's a strict requirement or just an recommendation, if it can be done by a novice like me, I will do it.

Now, what would be the best way of doing this? Some people said a fused spur would do, or maybe a switch in the line? Either way it will be installed in the loft so the alarm circuit can only be switched off there.

Thanks!

 

[JohnW2]

Look at 1.19 (Page 14)

Is that an actual regulation or another example of poor guidance?It does seem inconsistent with another part of the paragraph.

Part B of the Building Regs is almost as brief and vague as is Part P, and merely requires "appropriate provision for the early warning of fire". However, I don't know whether there are any other applicable sources of regulations (c.f. our BS7671), or whether what we're seeing in the Approved Document is just the creation of the author.

Kind Regards, John

 

[JohnW2]

Anyway, lets not start another debate about this here. Whether it's a strict requirement or just an recommendation, if it can be done by a novice like me, I will do it. Now, what would be the best way of doing this? Some people said a fused spur would do, or maybe a switch in the line? Either way it will be installed in the loft so the alarm circuit can only be switched off there.

A switch (preferably a 'double pole' one) would suffice, but if it's in the loft, it would hardly satisfy the spirit of the idea (be it a regulation or not). Would it not be possible to drop cable(s) down from the loft and have the switch high up on an upstairs wall?

Kind Regards, John

 

[bmoon]

A switch (preferably a 'double pole' one) would suffice, but if it's in the loft, it would hardly satisfy the spirit of the idea (be it a regulation or not). Would it not be possible to drop cable(s) down from the loft and have the switch high up on an upstairs wall?

Many thanks John. I see the point of double pole. But I guess it will be a switched & fused spur, rather than a junction box then a double pole switch?

To be honest I am a bit reluctant to put the switch on the wall, for the additional amount of work and also for the looking of the wall - there are already a few switches on the most feasible wall, adding another would make it like a switch board I'm afraid.

 

[Iggifer]

most (good) switched fused spurs are DP anyway, I know MK's are

High up on the wall wouldn't look too bad, it would also be easier to fit higher up

 

[JohnW2]

Many thanks John. I see the point of double pole. But I guess it will be a switched & fused spur, rather than a junction box then a double pole switch?

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.

To be honest I am a bit reluctant to put the switch on the wall, for the additional amount of work and also for the looking of the wall - there are already a few switches on the most feasible wall, adding another would make it like a switch board I'm afraid.

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.

Kind Regards, John