Which bits of domestic wiring does BS 7671 cover?

BS7671 does not prohibit bi-colour conductors.

Ah, good point. The bit my head had remembered turns out to be from a much earlier edition (and specific to flexes) and has long since been dropped.

It only puts a prohibition on the use of green-and-yellow.

So there remains a clash with the pair 18 of twisted-pair cables?

The only conductor functions specified in Table 51 are for power conductors, not telecomms

If that's the intention the wording could do with a lot of improvement - 514.4.4 makes no mention of power only, and indeed table 51 itself as well as having 4 sections for power circuits has another one specifically for 'Control circuits, ELV and other applications' - which I think I could be forgiven for reading as applying to any non-power circuits.

even the prohibition against a single colour green as identification has been removed for comms functions (see 514.4.5) for exactly the purposes you cite here.

It has indeed been removed from 514.4.5 - but has yet to appear in table 51 - which still makes it difficult to use green and still comply with 514.4.4 (given the current wording at least).

 

BS 7671 makes reference to requiring "augmentation" by other standards, which, by standards they reference, require the colours you are claiming BS 7671 prohibits

So it's sounding like these other standards are permitted not just to supplement BS 7671 but to modify it as well (i.e. override some BS 7671 requirements, not just add to them) - to pinch the wording from section 700.

yet those conductors are not "line" conductors.

Humm maybe - BS 7671's definition is so wide and given that any electrical signal requires the transmission of some (if very small) amount of energy I think that's going to be hard to prove on way or the other given the current wording. I agree it's not "intuitive" to regard comms signals as line conductors though (but quite where you'd draw the line I'm not sure).

 

An incoming BT line is outside the scope of BS 7671 ... assuming you are talking about the internal wiring, it may well be FELV. If installed in accordance with the recommendations of BS 6701, hopefully there are no exposed-conductive-parts, and no earthing necessary (earthing or bonding may be undertaken with the permission of the provider).


Don't forget, the reference standard BS 6701 refers to BS 7671 for safety.


Regarding RCDs, the question to ask, is whether the system is AC or DC - if the remote powering system, or ring voltage, is DC, then the RCD is perhaps not required by BS 7671?

Indeed - it was the internal wiring I was thinking of - the external line just being the "power source" as it were. As far as I've been able to find out UK standard telephone ringer signals are certainly a.c. - usually 25Hz and around 70-80V. Certainly modern phones have a lot less in the way of metalwork than older ones, but I think we still need to consider exposed-conductive-parts - if only the metallic front plates on some fancy (chrome/brass etc) wall sockets. (Unless BS 6701 overrides BS 7671 to say such precautions can be ignored.)

In terms of earthing, a "distribution system" should be earthed ..

Absolutely! (been there, done that, suffered the "tingle"...)

 

  - Andy.

BS7671 does not prohibit bi-colour conductors.

Ah, good point. The bit my head had remembered turns out to be from a much earlier edition (and specific to flexes) and has long since been dropped.

It only puts a prohibition on the use of green-and-yellow.

So there remains a clash with the pair 18 of twisted-pair cables?

The only conductor functions specified in Table 51 are for power conductors, not telecomms

If that's the intention the wording could do with a lot of improvement - 514.4.4 makes no mention of power only, and indeed table 51 itself as well as having 4 sections for power circuits has another one specifically for 'Control circuits, ELV and other applications' - which I think I could be forgiven for reading as applying to any non-power circuits.

even the prohibition against a single colour green as identification has been removed for comms functions (see 514.4.5) for exactly the purposes you cite here.

It has indeed been removed from 514.4.5 - but has yet to appear in table 51 - which still makes it difficult to use green and still comply with 514.4.4 (given the current wording at least).

 

BS 7671 makes reference to requiring "augmentation" by other standards, which, by standards they reference, require the colours you are claiming BS 7671 prohibits

So it's sounding like these other standards are permitted not just to supplement BS 7671 but to modify it as well (i.e. override some BS 7671 requirements, not just add to them) - to pinch the wording from section 700.

yet those conductors are not "line" conductors.

Humm maybe - BS 7671's definition is so wide and given that any electrical signal requires the transmission of some (if very small) amount of energy I think that's going to be hard to prove on way or the other given the current wording. I agree it's not "intuitive" to regard comms signals as line conductors though (but quite where you'd draw the line I'm not sure).

 

An incoming BT line is outside the scope of BS 7671 ... assuming you are talking about the internal wiring, it may well be FELV. If installed in accordance with the recommendations of BS 6701, hopefully there are no exposed-conductive-parts, and no earthing necessary (earthing or bonding may be undertaken with the permission of the provider).


Don't forget, the reference standard BS 6701 refers to BS 7671 for safety.


Regarding RCDs, the question to ask, is whether the system is AC or DC - if the remote powering system, or ring voltage, is DC, then the RCD is perhaps not required by BS 7671?

Indeed - it was the internal wiring I was thinking of - the external line just being the "power source" as it were. As far as I've been able to find out UK standard telephone ringer signals are certainly a.c. - usually 25Hz and around 70-80V. Certainly modern phones have a lot less in the way of metalwork than older ones, but I think we still need to consider exposed-conductive-parts - if only the metallic front plates on some fancy (chrome/brass etc) wall sockets. (Unless BS 6701 overrides BS 7671 to say such precautions can be ignored.)

In terms of earthing, a "distribution system" should be earthed ..

Absolutely! (been there, done that, suffered the "tingle"...)

 

  - Andy.