smoke alarms 17th contradiction

[fog]

Hi posted before
got loads of replies but still puzzzled on what we can do about feeding smoke alarms?

have put in some regs quotes from the excellent Amberleaf (please keep up the good work) and the confusing regs as usual.

"
Fire detection circuits must be supplied independently of other circuits and not protected by an Rcd protecting multiple circuits. 560.7.1
Fire detection cables, not including metal screened fire resistant cables, must be adequately segregated from cables supplying other circuits. 560.7.7
Except for TT systems, the circuit supplying a smoke alarm should not be protected by an RCD. For TT systems the smoke alarm must be supplied from the fixed equipment section of the ccu, not through a 30mA RCD. "

If we are to protect all circuits 30mA RCD if less than 50mm in depth of walls etc, how do we connect a smoke alarm in ccu bearing in mind the above, do we rcbo or mcb on a high integrity board any help on this confusion would be appreciated??

 

[pennywise]

If you don't want the smokes on an RCD put them in earthed metallic conduit just for the detector circuit down to the board or I just put them on the unprotected ways in the CU and have it on a RCBO.

 

[fog]

Thanks for reply
have been putting the smokes on unprotected rcbo , but what mA rating should this be?
more views are welcome

 

[pennywise]

30mA.It says in the bits you quoted that the only situation you cannot use a 30mA RCD is on a TT supply in which case you would use the metallic conduit method.

 

[Sintra]

30mA.It says in the bits you quoted that the only situation you cannot use a 30mA RCD is on a TT supply in which case you would use the metallic conduit method.

You can still put smoke alarm circuit on seperate 30mA RCBO on a TT if the routing of the cable requires it. If not put on seperate 100mA RCD. Or indeed use metallic conduit still with seperate 100mA RCD.

 

[frenchy]

Can you not just run the circuit in lsx or fp cable?

 

[pennywise]

Yep you could use Earthshield cable, I want to start using it pricey though.

 

[David.]

so how come alot of people put them on lighting circuits??

must have seen these types of threads a 1000 times but never gets resolved im still unsure on what is best practice tbh

 

[Des 56]

Fire detection circuits must be supplied independently of other circuits and not protected by an Rcd protecting multiple circuits. 560.7.1

Since when




On site guide page 66 quote
Where all circuits are protected by Rcds there is advantage in supplying fire detectors from regularly used lighting circuits

If the detector has battery back up (cat L) then it can be fed from a local lighting circuit
As long as that is accepted and implemented then there are no issues


I think the confusion arises because the regs are more orientated to fire alarm systems in buildings


If you insist on seperate supply (why I can't understand)
Most supplies for a domestic smoke alarm can be run in without the buried deeper than clause and the Smokes can go on an mcb if you wish ( Tn systems)
With a TT system where 30 m/amp RCd is required an Rcbo for the smoke circuit can be used

Just wire off the lighting and we can stop complicating the never ending issue with domestic smoke alarms and end the uncertainty that the emphasis on fire alarms in buildings causes wiring of smokes in dwellings

 

[Tester Steve]

Fire detection circuits must be supplied independently of other circuits and not protected by an Rcd protecting multiple circuits. 560.7.1

Since when


On site guide page 66 quote
Where all circuits are protected by Rcds there is advantage in supplying fire detectors from regularly used lighting circuits

Agree with Des. In domestic work, I feed the smokes from the ground floor lighting circuit via a keyswitch near the CU for isolation. Why this gets asked so many times beats me, seems simple!!

Steve.

 

[David.]

In domestic work, I feed the smokes from the ground floor lighting circuit via a keyswitch near the CU for isolation.

Steve.

this is a good idea and i like it. Could i ask though, if the smoke alarms are the detachable ones where the base plate is fixed and wired, then the "front" slides on, would you still need the isolation??

thanks in advance

 

[Spudnik]

this is a good idea and i like it. Could i ask though, if the smoke alarms are the detachable ones where the base plate is fixed and wired, then the "front" slides on, would you still need the isolation??

thanks in advance

Thats exactly as i see it.

Even the ones with the flyleads, can still be unplugged giving isolation.

Plus the fact that i cant think of ANY domestic smoke detector that has serviceable parts in them anyway.

I personally would only put local isolation on a fire system.

 

[trebor]

Hi posted before
got loads of replies but still puzzzled on what we can do about feeding smoke alarms?

have put in some regs quotes from the excellent Amberleaf (please keep up the good work) and the confusing regs as usual.

"
Fire detection circuits must be supplied independently of other circuits and not protected by an Rcd protecting multiple circuits. 560.7.1
Fire detection cables, not including metal screened fire resistant cables, must be adequately segregated from cables supplying other circuits. 560.7.7
Except for TT systems, the circuit supplying a smoke alarm should not be protected by an RCD. For TT systems the smoke alarm must be supplied from the fixed equipment section of the ccu, not through a 30mA RCD. "

If we are to protect all circuits 30mA RCD if less than 50mm in depth of walls etc, how do we connect a smoke alarm in ccu bearing in mind the above, do we rcbo or mcb on a high integrity board any help on this confusion would be appreciated??

I think there may be some confusion here between safety services Chapter 560 BS7671 and normal self contained smoke alarms, chapter 560 is cocerned with full fire alarm system circuits which are supplied via a safety circuit with back up such as gennys, ups etc

If your question is referring to interlinked detectors with internal back up battery then the building regs give the following guidance:

The power supply for a smoke alarm system should be derived from the mains electricity supply. The circuit may be a
1) single indepent cb supply
2) a regularly used lighting circuit

The advantage of 2 is that the circuit is unlikely to disconnected for any prolonged period as the failure of the associated lighting circuit will be obvious, there shouild however be a means of isolationg the smoke alarm s without isolating the lighting eg a key switch adjacent to the ccu

With this method if the lighting circuit is on an rcd or rcbo for any reason the loss of supply to the smoke alarms will be noted

Source NICEIC/ ECA Electrical Installers Guide to The Building Regulations

 

[mattyb129]

Hi posted before
got loads of replies but still puzzzled on what we can do about feeding smoke alarms?

have put in some regs quotes from the excellent Amberleaf (please keep up the good work) and the confusing regs as usual.

"
Fire detection circuits must be supplied independently of other circuits and not protected by an Rcd protecting multiple circuits. 560.7.1
Fire detection cables, not including metal screened fire resistant cables, must be adequately segregated from cables supplying other circuits. 560.7.7
Except for TT systems, the circuit supplying a smoke alarm should not be protected by an RCD. For TT systems the smoke alarm must be supplied from the fixed equipment section of the ccu, not through a 30mA RCD. "

If we are to protect all circuits 30mA RCD if less than 50mm in depth of walls etc, how do we connect a smoke alarm in ccu bearing in mind the above, do we rcbo or mcb on a high integrity board any help on this confusion would be appreciated??

make every breaker on adomestic board i presume you are talking about a rcbo except for the smoke alarm circut problem solved

so how come alot of people put them on lighting circuits??

must have seen these types of threads a 1000 times but never gets resolved im still unsure on what is best practice tbh

some people just cant be bothered to run a 3 core to the upstairs one and take it of the lighting circut as most new builds are pigs to rewire anyway i find it a lot wen i do testing

 

[Des 56]

We have put our own views so,to anyone who may still be confused
These are the statements from the safety council that should give clear understanding of the situation with regard domestic smoke alarm circuits
Question
Does the 17th Edition permit connection of smoke alarms to an adjacent lighting circuit taking into account Regulation 560.7.1, which states that circuits of safety services shall be independent of other circuits?


Yes. The particular requirements of BS 5839-6 take precedence over the general requirements of BS 7671.

There are no particular requirements or limitations in BS 5839-6 concerning the use of RCDs with Grade D fire detection and alarm systems.

Supply question
The options
1) an independent circuit at the dwelling’s main distribution board, in which case no other electrical equipment should be connected to the circuit (other than a dedicated monitoring device installed to indicate failure of the mains supply to the smoke and/or heat alarms), or
ii) a separately electrically protected, regularly used local lighting circuit.

We recommend option ii) on the grounds that disconnection of the supply to the fire detection and alarm system will be more readily noticed. In our opinion ‘separately electrically protected’ does not preclude sharing an RCD with several other circuits where this is permitted by BS 7671