Connecting Smokes - Hager Guidance

[Piratepete]

Hi Guys
Hager's Consumer Unit Guide to the 17th Edition makes the statements on page 11

According to BS 5839, circuits supplying fire or smoke alarms in
dwellings can be protected by an RCD provided that either:
i. The RCD serves only that circuit. For example with the use of an
RCBO
ii. The RCD should operate independently of any RCD feeding
socket outlets or portable equipment

As one who has always connected them to the upstairs lighting circuit, which is on the same RCD as the downstairs sockets, it's made me question what I'm doing. It's requirement ii. that has attracted my attention.
I don't have a copy of BS 5839.

Can anyone shed light on this, please?

Ta

Pete :skep:

 

[AndyL]

5839-6 recommends avoiding the use of RCDs for fire system circuits other than Grade D ( mains powered with back up)
Most domestic installations likely to be Grade D

 

[Piratepete]

Hi AndyL
I think you misunderstood my query. I do use grade D. This is what Hager says -
ii. The RCD should operate independently of any RCD feeding socket outlets or portable equipment
This would not allow you to use boards with dual RCDs where you split your socket circuits between the 2 RCDs.
Pete

 

[tazz]

The idea here was that most split boards 16th had lighting on non rcd side, so lighting and smoke complied in grade D when wired to a mcb only. Now with using RCBOs in 17th boards, the lighting and again smokes must be dedicated to that one RCBO and not a common RCD feeding other circuits.

 

[Piratepete]

The idea here was that most split boards 16th had lighting on non rcd side, so lighting and smoke complied in grade D when wired to a mcb only. Now with using RCBOs in 17th boards, the lighting and again smokes must be dedicated to that one RCBO and not a common RCD feeding other circuits.

Hi Tazz
Ahh!
So are you saying, as Hager does, that if I'm installing smokes in a domestic property, I should buy a high integrity board and connect the smokes and upstairs lights to their own RCBO leaving the rest of the circuits split across the 2 RCDs? (It's too expensive to put all circuits on RCBOs)

If so, I've missed a requirement of BS5839 since the 17th Ed came out, and so have many other electricians! I haven't come across any 17th Ed CUs where the smokes are on a RCBO. Most folks seem to buy the 'bargain of the day' mcb populated dual RCD board and connect the smokes+upstairs lights and downstairs sockets to the same RCD!

It hasn't been picked up on my NICEIC assessments either! I can see a retrofit coming up to my rewire jobs! Ouch!

Pete

 

[tazz]

If your using a dual board one section is feed from a isolator, the other from the RCD, so lighting should be on a mcb or rcbo. With sockets etc feed from RCD. To be honest, i would not call this a grave variation from part 6, but the idea is to prevent dodgy appliances tripping rcds and leaving smokes unpowered. Alan pointed out under grade D, this is not a major issue these days, as the detection must show loss of power by audio/visual means