smoke alarms on different circuits?

[kevindgas]

so the situation is a domestic house with upstairs smoke on upstairs light circuit, downstairs smoke on downstairs light circuit
the linkwires are just loose in each, no isolation from lights on either.
both light circuits are on same bus bar no rcd protection just a 100A double pole switch
customer needs it signed off for BuildingControl

can't find any info in any of the books on how to deal with this?

if i link the 2 alarms by a wire on the activation wires will this cause a problem of voltage crossing between the circuits if one is turned off?
if i don't link them then surely that isn't acceptable either?

thanks for any sensible suggestions on this one!

 

[Taylortwocities]

The only time I've seen a working smoke system with two sparate supplies has been with Radiolink bases.

Think you might need to call the manufacturer. I rather think it'll be a problem. If nothing else, a later upgrade to a multi-RCD/RCBO CU may cause the RCD/s to trip.

BTW, how did they run the link wire, just a single conductor?

 

[kevindgas]

no link wire that is part of the question

 

[Alarm]

Cannot be sure on the specific regs for you in this instance.

But if both live and the interconnect is in series all will activate. One line off and only the top or bottom will activate. As you probably know, as long as the interlink is connected.
You should not get a cross voltage.

You could fit a radio base to each separate circuit and then let them connect wireless. One base per circuit.

www.aico.co.uk

 

[kevindgas]

thanks alarm, so the link wire isn't connected directly to the LNE then? wasn't sure hence the question, haven't come across this before!

 

[Taylortwocities]

I still think you need to check with the manufaturer. The interconnect wire cannot operate on its own. I cannot find any docs that refer to how this is achieved.

There has to be voltage/signalling on this conductor and that will (probably) operate with the neutral link as the reference (0v). This will cause issues if the interconnect current is >30mA as RCDs are present (think of future CU upgrades).

As I mentioned before (and reinforced by Alarm) Radiobases may be the solution that meets the manufacturer's. Probably cheaper, at this stage, than chasing in a new run of 3C&E cable.

 

[PrenticeBoyofDerry]

If you are going down the route of interlinking them, I assume you will need to route cable between the smokes? So if that is the case, I would disconnect one of the supply cables to one of the smokes and run 3 core/earth between them, so they are powered by one circuit only. This will avoid, isolation problems and in the event of RCD protection being introduced, trip issues.
You have stated that there are interlink cables but loose, have you checked that this cable is one of the same via continuity? Just because you have seen this cable does not mean they are both one of the same.

 

[Lectrician]

Radio bases would be the quickest way to put your mind at rest.

The interlink core is not mains voltage, it is ELV. Remember, during a power failure the interlink has to still work! If you look at the recommended colour code for smokes, the brown is live, the grey sleeved blue is neutral and the black with no sleeving is the interlink (black being a ELV colour). Most manufacturers show this.

I believe the ELV signalling uses a reference to the neutral too, but that any current is beond negligable. This is why if you reverse the polarity between interlinks you can frazzle the smokes.

I would say it would work fine in this manner, although it is not installed as per the install instructions I would guess.

 

[kevindgas]

prentice when i say loose i mean just the connector cable I:E just 6" of cable at each alarm!
yes i agree that the safest way is to run a new supply between them and power off one circuit. but i need a reason to fail it that holds water!
as they say you can make things idiot proof but a better class of idiot then appears!!

 

[Taylortwocities]

Just fail it as it does not comply with BS 5839: Pt.6: 2004
or the manufacturer's instructions => BS7671

Not sure of the nature of the building works but if architect plans it should have defined interlinked alarms.

Whoever wired it up obviously did not test them. If he signed to say they complied then his @rse should be on the line.

 

[kevindgas]

exactly what i thought, found out that the custs brother did the work!! now i have to find the cheapest/easiest route to putting it right!!

think the only solution will be a new 4 core cable between them and scrap one of the supplies plus of course an isolator somewhere in the system.

 

[Taylortwocities]

You dont want an isoator in the system.

Normally they are directly wired to a regularly used lighting circuit. An isolator can be turned off and nobody will notice. Until the fire investigators come around

 

[vibrobullit407]

Why 4 core? you only need to run line, neutral and interconnect between the smoke alarms. As mentioned above might be easier to supply RF bases due to damage caused running in the 3 core cable.

 

[Taylortwocities]

Think he means 3core and earth.