smoke detection/rcbo yes or no

[electrosparks]

HI SPARKYS
JUST A QUICK BIT OF ADVICE REQUIRED.
HAVE RECENTLY BEEN TO PRICE A DB CHANGE OF THE DUAL SPLIT LOAD VARIETY.and noticed the instal has a dedicated smoke detection circuit .Now i have also noticed that this circuit is buried in plaster (through a safe zone) and in fact all circuits are buried in plaster as the feeds drop down the wall from ceiling to db level. In no way could I claim that cables are 50 mm back from surface or would be in earthed steel containment
Now due to the circumstances I feel obliged to put smoke detectors on rcd protective device but realize safety services are not required to have additional protection.

Would it be better to put smokes on a rcbo as cables are not 50mm back
Or would it be right to leave circuit without additional protection.

Just for the record I fully believe in the use of 30ma rcd/rcbo and have done for the last 25 years or so as as I believe electrical safety takes precedent over nuisance. I also realize that sometimes incorrect selection of rcds can cause problems to some equipment including fridges and computers etc, and grouping circuits protected by rcds can have a negative impact with some equipment .
So if I put circuit on rcbo and in the future an earth fault was to occur the device was to trip indicating earth fault wouldn't that be better than if left unprotected and the same fault was to occur the protective device may not trip and potentially dangerous leakage currents may be present but smoke detectors still function, whats the point a safety service that can kill you.
I think in this case circuit should be rcbo protected but I have been wrong before.
Anyway sparks what is right db config or if any one wants to get it off their chest what should it be?:shocked:

 

[telectrix]

if you want the smokes RCD protected, trhen you must use a RCBO so that a fault in another circuit can't take the smokes out. at the end of the day, it's your call.

 

[Geordie Spark]

if you want the smokes RCD protected, trhen you must use a RCBO so that a fault in another circuit can't take the smokes out. at the end of the day, it's your call.

Thank God for that ...... it looks like I've finally done something right !!!

 

[MDJ]

I would avoid at all costs installing a smoke on a RCD, however if the method of installation means it needs to be protected via this method then 100% agree with tel.

 

[driverman]

Many sparky's say put smokes on a RCD / RCBO lighting circuit.....reason being client will take action if said light circuit not working thus ensuring supply to smokes. The other school of thought is, if on a dedicated RCBO and it operates for whatever reason, Client may not be aware that supply to smokes has been interrupted. Having said that, mine at home are on a dedicated RCBO.

 

[brucelee]

RCBO dedicated circuit or a regulary used lighting circuit protected by RCD either way is acceptable

 

[tazz]

This is were both regs come together, all wiring must meet IEE, so if an RBO or RCD is required, then it needs fitting....The BS5839 fire alarm euipment must indicate the loss of power. Personally I would fit an mcb on the non rcd side.

 

[Stroppy]

If the alarms have a built-in non-removable battery they will beep when power is lost, satisfying the 'indicate the loss of power' requirement, otherwise power them from a circuit with frequently used lights on.

 

[Outspoken]

RCD/RCBO on a life safety system...Pathetic. Next we will all need to wear Hi Vis jackets to walk on the public street FFS.

 

[telectrix]

i quite agree but reg. 522.6.101,102 and 103 say otherwise.

 

[Outspoken]

i quite agree but reg. 522.6.101,102 and 103 say otherwise.

Not having a Regs book to hand at the moment I cannot look up the exact wording, but I would point out the the 17th Ed states the following in respect of the use of RCDs;

Basic Protection: These may only be used as additional protection and must have an operating current of 30mA or less and an operating time of 40mS or less at 5xIΔn

Fault protection: Used where the loop impedance requirements cannot be met for for protecting socket outlets supplying portable equipment used out doors.

Now a dedicated circuit for a smoke detector does not fall under either of those because by placing the circuit on a suitably rated MCB you would meet the needs of the regulations in terms of protection against fault conditions.

Now under 522.6.101 and 102 we have the requirement that cables buried less than 50mm into a wall without mech protection (lets ignore the comments about competent people) are required to be protected by an RCD, however as the smoke detector will be likely on a ceiling unless the cable is significantly in a wall likely to be drilled into then I do not see any need to install an RCD/RCBO on the circuit. Proper design/planning should actually eliminate the need for the RCD

 

[Darkwood]

It all comes down to class and category the building and residence situation falls under ... now the cable will need rcd protection but as for the separate rcbo it in most domestic situations is not necessary although as with others I will agree it is good design, a lot of people forget the detectors will have battery back-up and will be good for many months without mains power hence you can link a mains powered detector onto the local lighting circuit as any tripping of the circuit will be reset promptly if house is occupied and it doesn't effect the ability of the detector to operate.

 

[Darkwood]

Not having a Regs book to hand at the moment I cannot look up the exact wording, but I would point out the the 17th Ed states the following in respect of the use of RCDs;

Basic Protection: These may only be used as additional protection and must have an operating current of 30mA or less and an operating time of 40mS or less at 5xIΔn

Fault protection: Used where the loop impedance requirements cannot be met for for protecting socket outlets supplying portable equipment used out doors.

Now a dedicated circuit for a smoke detector does not fall under either of those because by placing the circuit on a suitably rated MCB you would meet the needs of the regulations in terms of protection against fault conditions.

Now under 522.6.101 and 102 we have the requirement that cables buried less than 50mm into a wall without mech protection (lets ignore the comments about competent people) are required to be protected by an RCD, however as the smoke detector will be likely on a ceiling unless the cable is significantly in a wall likely to be drilled into then I do not see any need to install an RCD/RCBO on the circuit. Proper design/planning should actually eliminate the need for the RCD

You will need to run the linking cables from floor to floor and in doing so in domestic usually will fall in a wall etc <50mm thus requiring rcd protection.

 

[Outspoken]

You will need to run the linking cables from floor to floor and in doing so in domestic usually will fall in a wall etc <50mm thus requiring rcd protection.

When I can I will look this up properly as I am at work at the moment. I do not do domestic work and haven't for years as I hate it with a passion, but I'll bet that there is a compliant work around.

 

[tazz]

With better technology in batteries are charging circuits, the BS suggested, in 2002 that most modern fire systems where capable of meeting standby conditions, exceeding 24hrs for L cat and 72 hours for P cat. And the days of coming straight off the bus bars were obsolete. Their aim was not to make the installed system the caurse of a potential risk. So it is now preferable to now come from a essential db (if fitted) or a non essential db via a dedicated mcb using enhanced cable. All modern fire alarm panels and part 6 detection must give and audio and visual indication of power loss.