help! with kidde smoke alarm wiring install

[BobTBuilder]

during initial installation, from consumer unit right through to the end of the circuit, is there any need for an earth wire at all? as i've got twin and earth that I can use from consumer unit to the first alarm, but i also have three core n/l/e each sheathed in the cable which i'm looking to use to interconnect the other two alarms, rather than use trip+earth (bulkier)
in this instance could i not utilise the sheathed earth as the connector?

 

[oasistechnical]

no you cannot!!!

you must use a three core + earth cable from the consumer unit (or lighting junction box) to each of the detectors.

link earths back to the board and connect them together with a terminal block, or crimp.

do not use the CPC as a conductor!!!

see BS5839 pt 6 for more information

john h
fire and security systems engineer

 

[DetlefSchmitz]

As above. The first cable from CU to first alarm can be twin and earth though.

 

[BobTBuilder]

so given that it states that the alarms are double insulated and do not require earthing, why include an earth wire in the cabling used at all? what is it protecting?

the set up is a 1 way non returning circuit with an interconnect running from 1st unit to 2nd then from 2nd to 3rd etc.

given that the earth serves no purpose, why not use a 3 core cable where all wires are insulated independantly within the cable?

what am i missing here? is there a different composition to the earth wire?

 

[DetlefSchmitz]

You are missing two points:

1. The cpc is required for circuit testing.

2. A wire marked as being an earth wire may not be used for any other purpose.

 

[BobTBuilder]

i accept what you say, but....

if the cpc is not being used at all within the creation of the circuit, ie. twin and earth to connecting block, but the earth never passes the connecting block, the same on each subsequent interconnection. the only continuing wires are live, neutral and connector.

given this, i fail to see what you could test the cpc for as it does not engage with any of the units, and the circuit terminates at the last unit. i assume that the cpc will terminate at the junction block to the last unit, or does the cpc alone return to the CU?? ...or am still missing something here....

 

[Lectrician]

To comply with the regulations you must not use an earth conductor for any other purpose than an earth. You must also provide an earthing facility at all points weather this is used or not.

 

[bernardgreen]

i accept what you say, but....

you dont want to follow advice from people who know the way to install the system

given this, i fail to see what you could test the cpc for as it does not engage with any of the units,

If you can't see the way the cpc is used in testing then your knowledge is in-adequate to install any electrical circuit....

Without the CPC acting as a reference it is not possible to locate some faults.

TAKE ADVICE

 

[DetlefSchmitz]

Without going into the whole business of testing, which would involve a college course worth of answers which I don't have time for...

What you are still missing is that these points are regulations in BS7671. So have to be obeyed. Wiring up these alarms without Building Control approval is probably illegal anyway. That's not my concern - but at least you can do it within the Wiring Regulations. Firstly for other people's safety, and secondly to avoid problems if you get caught out.

Basically you asked whether you could do it a certain way - and the answer is no.

 

[sparkwright]

As mentioned, you use twin and earth from mains to first detector, then you 3 core and earth from here to all other detectors.

You cannot use the earth wire as anything else, it could be dangerous if anyone spliced into that cable thinking it was earth wire.

All the earth wires in the circuit must be connected throughout it's entire run. They must also be sleeved with green and yellow sleeving.

Just get the correct cable.

 

[BobTBuilder]

thanks all, i'm not doing the wiring myself, i'd probably electrocute myself! i have someone qualified coming in to do it, its just that i couldnt get hold of him today and had cracked open the packaging and was looking over the instructions.... which with my limited knowledge was probably a mistake, i just can't stand not being able to get my head around something

 

[Lectrician]

BobTBuilder - Stick to bricks and blocks, not heats and smokes.

 

[BobTBuilder]

cant seem to find any white triple and earth, but found a supplier selling grey labelled up as smoke....this ok?

 

[ban-all-sheds]

Why do you want white?

 

[BobTBuilder]

seen a white cable labelled up low smoke and fume harmonised, whilst most grey cables have no such description at all...