I have a number of smoke alarms to fit. It seem to be that most people are wiring them in 3C&E. Fortuitously it seems I have a convenient source of power near each one, so one really only needs to run a cable for the interconnect. Just wonder what cable people prefer to use in this case?
Smoke alarm interconnect
- Thread starter ekmdgrf
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3 core and earth.
Or radio bases if you're lazy.
Mains smoke alarms have to come of their own circuit/mcb if you want to meet the current regs, 3 core + earth is used as RFLighting mentioned.
Also having them on different circuits can be dangerous and may cause trouble with RCD's as you will have shared the live interconnect between different circuits what will then return to neutral through one of the other circuits neutral, what will trip the RCD's if the circuit of the other smoke alarm is on a diffrent RCD and the interconnect becomes live in a alarm condition.
Also you pose the risk of some one thinking a circuit is safely isolated, when the interconnect and thus the return path through neutral could become live from a another smoke alarm on a active circuit. (effectively, causing a possible borrowed live.) This is amusing you get current flowing from the interconnect terminal to neutral without the permanent live being live.
3 Core + Earth wiring
Brown = Live
Grey (Sleeved blue) = Neutral
Black (Sleeved brown) = Interconnect/Link
Also having them on different circuits can be dangerous and may cause trouble with RCD's as you will have shared the live interconnect between different circuits what will then return to neutral through one of the other circuits neutral, what will trip the RCD's if the circuit of the other smoke alarm is on a diffrent RCD and the interconnect becomes live in a alarm condition.
Also you pose the risk of some one thinking a circuit is safely isolated, when the interconnect and thus the return path through neutral could become live from a another smoke alarm on a active circuit. (effectively, causing a possible borrowed live.) This is amusing you get current flowing from the interconnect terminal to neutral without the permanent live being live.
3 Core + Earth wiring
Brown = Live
Grey (Sleeved blue) = Neutral
Black (Sleeved brown) = Interconnect/Link
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Eveares, what voltage do you think the interconnect uses?
While I agree they should be on the same circuit if wired together using a hard wired interlink, with radio bases, you can mix supplies (the whole intention of the radio base).
The interlink is ELV. This is how it interlinked in a power failure. Pointless if it couldn't. This in mind, the interlink should not be sleeved brown, but left black, as this is an ELV colour.
While I agree they should be on the same circuit if wired together using a hard wired interlink, with radio bases, you can mix supplies (the whole intention of the radio base).
The interlink is ELV. This is how it interlinked in a power failure. Pointless if it couldn't. This in mind, the interlink should not be sleeved brown, but left black, as this is an ELV colour.
Is it any more a sin to have alarms powered from different sources with an interlink than it is to have two PCs on different circuits interlinked with an Ethernet cable or two mains powered telephones interlinked with telephone wire?
How does that work when the alarms are running on batteries only due to mains failure?
The actual voltage on the interlink is irrelevant (and may vary between manufacturers).
The interlink wire is not isolated from the mains voltage; it should be regarded as being part of the mains voltage wiring, and run and insulated accordingly.
PCs linked by Ethernet will isolate the Ethernet wire from the PC by 'magnetics' (transformers) in the network socket or on the network interface card; mains powered phones will isolate the phone line side from the mains power side (there would be serious trouble if mains voltage ended up on a phone line).
If you want to interlink smoke alarms using 'extra low voltage' then most manufacturers have relay link basis which provide isolated volt-free contacts for the purpose.
The interlink wire is not isolated from the mains voltage; it should be regarded as being part of the mains voltage wiring, and run and insulated accordingly.
PCs linked by Ethernet will isolate the Ethernet wire from the PC by 'magnetics' (transformers) in the network socket or on the network interface card; mains powered phones will isolate the phone line side from the mains power side (there would be serious trouble if mains voltage ended up on a phone line).
If you want to interlink smoke alarms using 'extra low voltage' then most manufacturers have relay link basis which provide isolated volt-free contacts for the purpose.
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What reg is that please?
I cant see a situation where alarms would be powered from diferent circuits yet have a common interlink wire. Surely if one has gone to the trouble of running in a separate interlink wire to each smoke they may as well have run a 3c&e to each fitting, meaning that there would be no need to power each detector from a different or local circuit?!!
Inverter?
Each luminary, which is conveniently located near where the detector goes has a nearby JB, which provides for power. It's a little less hassle running a single interlink cable than 3C&E and also avoids running two 3C&E cables in to each detector (it's a little cosy in there). It's also a real pita drilling many 3C&E sizes holes in the beams.
So in short, it seems like less agro for this job, so trying to figure out of it's permissible?
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