Safety service

John Peckham said:

And yes to SPDs if you have smoke alarms in your house.

Even Grade F1 and F2 which aren't connected to or part of the LV installation?

John Peckham said:

Nothing to do with the cable type supplying Safety Service. Emergency lighting, unless the supply is from a Central Battery Service or a UPS, is usually  in T&E.

Agreed, but Chapter 56 would still apply - which would ordinarily preclude the use of a domestic lighting circuit from being a "circuit of safety services", particularly Regulation 560.7.7. The lighting circuit(s) would also be required to be shown on a separate single-line-diagram adjacent to the CU 560.7.9).

We can't pick and choose which bits of BS 7671 we apply ... since we didn't think Chapter 56 applied to the lighting circuit supplying Grade D1 and Grade D2 systems, why would we choose now to interpret this differently just because there's a new requirement in Chapter 44 ?


For the avoidance of doubt, I think that it's time SPDs were installed in installations anyway ... and Grade D1 and D2 fire detection & alarm systems have electronics in them ... so I'm not arguing against it.

I'm just struggling (quite a lot) with the differentiator between classing it as a Safety Service, and the application of Chapter 56, vs Chapter 44 ?

The ONLY derogation I could see with the requirement for Grade D1 and D2 systems using a lighting circuit, over other safety services, would be 560.7.1 ... but, to-date, we have chosen not to implement the remainder of Chapter 56 for the lighting circuit that supplies such systems?

Let's please be consistent with how we are interpreting BS 7671 ... I am happy if we are now deciding that previously we were wrong (although that does make a lot of installations non-compliant, where current and previous guidance stated otherwise).

Nothing to do with the cable type supplying Safety Service. Emergency lighting, unless the supply is from a Central Battery Service or a UPS, is usually  in T&E.

For you argument to work a safety Service would be defined by the cable type supplying it rather than as Defined in Part 2 of BS 7671 and the list in Chapter 56.

Not defined by its cable type, but the cable type is a direct consequence of the definition - if we consider a domestic battery backed-up smoke alarm to be a safety service and the cable that supplies it is a circuit of a safety service then 560.7 and 560.8 would apply and we'd have to go down the FP/pyro route. Since all the advise and guidance says otherwise, there must be something wrong somewhere...

(I suspect that chapter 56 (and associated guidance) was written with only the problem of maintaining power to the device in mind, and now BS 7671 has expanded to consider other effects (e.g. damaging spikes/surges) that might disable a safety service even though the backup supply remains intact, it might be time for a rethink).

   - Andy.