Smoke Alarms

oldbutwise · Jul 21, 2011

when fitting a new dual rcd split board the smoke detectors are off the lighting circuit. Does this require a seperate rcbo or can i put the circuit onthe same rcd as one socket circuit ???? :Mr-T:

alanl · Jul 21, 2011

Could you say that a little clearer please?
It seems like you have one side RCD protected, the other not?
Or are both sides RCD protected?
Or do you want to put it on a socket outlet circuit?

tony mc · Jul 21, 2011

Put them in with the lights.

I take it you mean that the split is down sockets & up lights on the same RCD .

They will have battery backup if the cct trips or the RCD and you will know something is wrong as the lights will be off aswell!!!

tanglewood · Jul 21, 2011

Hi, when you say 'off the lighting circuit', do you mean the smoke alarm circuit has been doubled up off the same MCB at the consumer unit? or do you mean the first detector on the circuit is fed from a local light fitting, and then interlinked between the units with 3 core & E ? If it has been doubled up at the consumer unit then you need to seperate it from the lighting circuit (segregation of circuits) and fit a seperate 6a MCB. It is also a recommendation to install the MCB on a NON RCD covered circuit so as not to lose power due to a fault. So your split load dual RCD consumer unit should be arranged as follows :- Main switch, MCB (smoke alarm circuit) RCD (power and lighting etc ), RCD (power and lighting etc ) Remember to label the circuit at the consumer unit as a dedicated circuit for smoke alarms only. Hope this helps.

oldbutwise · Jul 22, 2011

Thanks for all the help. Sorry for makin it so complicated but its a split board with main switch and two rcd units.
Read somewhere that BS 5839 (i think thats the one) doesnt like smoke alarms on the same rcd as socket circuits.
Cant put in mcb cause wired in t/earth and not 50mm deep so have to put rcbo GETTIN EXPENSIVE NOO!!!!!

:drummer::drummer::drummer::drummer:

alanl · Jul 22, 2011

There is no need to put it on a dedicated circuit, 7671 gives the option of having it on a regularly used lighting circuit (clearly, so long as there is adequate capacity on the circuit).
The advantage to this is that if the smoke alarm goes faulty, it is more likely to be fixed correctly, as people generally do not want to turn off a circuit breaker to lights, but they would do it, and forget about a dedicated smoke alarm circuit that is faulty.
In the real world, there are very few RCD trips, so nuisance trips by another circuit should not be a problem - if they are, then it is usually appliances causing the fault, and people would be quickly persuaded to do something about the errant appliance if it did keep tripping and causing them time to reset the system.
Alan.

tanglewood · Jul 22, 2011

hi alan, completely agree with you, I was just trying to make sense of what was going on from the description given, as a qualified electrician I was trying to give advice from experience. It seems like he was replacing an existing board with a 17th edition dual RCD board which in itself can be problamatic (shared neutrals etc) In the real world of us sparkys I try to make segregation of circuits as easy as possible. I agree with you about the 7671 reg but was just trying to give informed advice from information given. kind regards.