smoke detectors on lighting circuit. -Switched?

[1Justin]

I've been reading forum posts on domestic smoke alarms and also the Approved Doc B and the regs. I'm still confused one one or two points.
..So it seems it IS OK to run them off a existing RCD. This seems to be the most common way nowadays to do it - with it's own circuit/MCB.

But Approved doc B 1.19 says that detectors can also be powered from a lighting cct.
http://www.planningportal.gov.uk/uploads/br/BR_PDF_ADB1_2006.pdf









But then Doc B also says it should have independent means of isolating the power. How could this be so if it's off a lighting circuit? Does this imply it should have a lighting switch so Mrs Smith can just turn it off? - Seems a bit dim to me. Do people really put in an on/off switch?if they power it from the lighting circuit?

 

[malcolmsanford]

The key word is not switch but "isolating".

It is generally accepted that by the action of removing the head from the base your disconnecting the power, which you are has the power is left at the base not the head anymore, from the lighting circuit.

Also a lot of guys come off the lighting circuit at the CU, especially if there are no spare ways available, into a key switch sited next to the CU and then on into the smokes. that way they definitely comply, and if you use solid smokes that can not be detached from a base.

 

[i=p/u]

i wouldnt say it comes down to switch and back up but you could maybe have a fussed connection unit somewhere....

i have a house in sight for upgrading soon(yes im some sales man lol) and the smokes arnt a ment to be on rcd so does mean i require a 3 way split board with 2 rcd sides ....

b

 

[1Justin]

Hi Malcom,

I like your interpretation. On that basis it's OK to just fit the detectors into the lighting radial (RCD protected), -provided it lies in the right place of course. And isolation would be via removing the detector block connector in the ceiling.

Anyone fitting a new circuit/MCB for the detectors is possibly doing more than strictly necessary.

Perhaps I just read too much into it then.

Rgds

 

[i=p/u]

rcd protected hmmm

 

[DaveyD]

Agree with Malcom. Aico are isolated by just pulling off the base. I checked a while back with their tech dept and they said that was correct and was designed for isolation to meet regs.

I have put on seperate circuit and lighting circuit - both meet regs. I prefer lighting so that the end user cant just switch off if there is a problem and subsequently forget them

 

[malcolmsanford]

rcd protected hmmm

I let the fuse spur slip by .........but what does that mean?

 

[1Justin]

Thanks.. And after more Google fumblings.

..My understanding now is lighting circuit + RCD is OK, provided it's not taken from a side of CU which also protects sockets circuits.
If sockets are split to both CU sides, then separate RCBo is required for smoke detectors.
?

 

[BACON]

Don't forget the link wire from unit to unit

 

[malcolmsanford]

Don't forget the link wire from unit to unit

They may be RF and not require a link cable. Think most guys here now fit that type, saves a lot on install costs

 

[DaveyD]

Thanks.. And after more Google fumblings.

..My understanding now is lighting circuit + RCD is OK, provided it's not taken from a side of CU which also protects sockets circuits.
If sockets are split to both CU sides, then separate RCBo is required for smoke detectors.
?

Interesting - what regulation covers that?

 

[davelerave]

i was on the EI website recently and they state that the rf link is more reliable than the wired link-i never looked at it that way myself previously

if they're on a lighting mcb i always run a separate radial for alarms(for wired interconnect) and bunch them with the lights at mcb

 

[1Justin]

Interesting - what regulation covers that?

Hi Davey
I think that particular point isn't explicitly spelt out in regs, but I found this very clear interpretation:
17th Edition Consumer Unit Guide Hager

Tell me what you think.
Rgds