The IET is carrying out some important updates between 17-30 April and all of our websites will be view only. For more information, read this Announcement

Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 23 replies
  • Subscribers 31 subscribers
  • Views 2111 views
  • Users 0 members are here
Options
You may also be interested in
This discussion is locked.
You cannot post a reply to this discussion. If you have a question start a new discussion

Which bits of domestic wiring does BS 7671 cover?

AJJewsbury
As BS 7671 has been gradually extending its scope over the years, so we're now just about at the point that it covers any electrical installation that isn't specifically covered by another (BS?) standard (to paraphrase section 110) - and specifically mentions communication, signalling and control fixed wiring. So I'm trying to figure out what standards apply to what:


A few examples:
  • Power and lighting - yes, I'm happy that's just BS 7671.

  • Phone cabling - comes under BS 6701 that seems clear enough (maybe in addition to BS 7671, but there's room for deviation from BS 7671 demands all the same)

  • ELV intruder alarm wiring - I've come across BS EN 50131 series but can't tell (without paying a fortune) whether that covers just individual components or also acts as an installation standard - anyone know?

  • Fixed speaker wiring (say from a wall or ceiling speaker to 4mm sockets/binding posts on the wall behind the hifi)

  • UHF co-ax (i.e. TV aerial/satellite)

  • LV control wiring for CH systems (I'm guessing this is BS 7671 although every EICR I see seems to suggest otherwise)

  • Likewise similar wiring - e.g. pump/valves for solar thermal systems, air-con or heatpumps.

  • ELV heating control wiring (e.g. from 12V 'network' type room 'stats to underfloor heating manifold controllers)

  • Structured cabling (CAT 5 kind of thing) - usually done to TIA/EIA-568 - am I right in thinking that BS EN 50173 is equivalent?


Anyone know of some standards that would apply to these instead of (or in addition to) BS 7671? Or on paper at least, should I be looking to find sheathed speaker cables, IP2X binding posts and a suitable 30mA RCD for when they're concealed in the wall (as far as I can tell the amplifier isn't a SELV source), intruder alarm contacts that don't rely on the timber door frame to complete the enclosure, or co-ax that complies with BS 5467, 6724, 7846, 8436 or 60702-1? ?


   - Andy.
  • 0
    It is all just too complicated and will deter future electricians from becoming interested in the industry. All these B.S. numbers and references and clauses are worse than the law. Wiring regulations should be simplified not made ever more convoluted and difficult to understand and apply. B.S. 7671 is like reading a blinkin difficult physics book these days. It has lost the plot, as has the I.E.T., BIG TIME.


    Z.
  • 0
    Thanks Graham - that's very useful.

    BS 6701 reinforces or augments BS 7671 requirements. There are no "conflicts". BS 6701 actually refers to BS 7671 as a requirement.



    That puzzles me - as I thought the only bi-colour allowed by BS 7671 for conductor identification was G/Y (for protective conductors) - so how does that sit with CW1308 etc cables with their bi-colour dots and backgrounds (I can't see how they comply with table 51, which seemingly 514.4.4 insists on) - indeed if you have a large enough cable pair 18 is green/yellow coded (if by dots rather than stripes) so and additional conflict with 514.4.2 there it seems. Likewise I don't think BS 7671 permits the blue core of my alarm cable to be used for anything other than "neutral". (It seems a bit in two minds over green as well.) Then as far as I can tell, an incoming BT line doesn't meet BS 7671's rather specific requirements for a SELV or PELV source (and presumably unlikely to give a ringer signal of up to 80V a.c.)  let alone many mains powered answering machines etc - so seemingly I must treat it fully as FELV if I'm to comply with BS 7671 chapter 41 - so I need cables insulated according to the voltage of the 'primary circuit' (mains?) and all exposed-conductive-parts earthed? Then, as you say, there's the 30mA RCD issue where the cables are concealed in walls.


    Similarly the TV, aerial amplifier, sat box etc don't obviously meet BS 7671 limited definitions of SELV/PELV sources (and several inject a d.c. voltage to power LNBs, masthead amps or remote control eyes, so we can't really presume the only power source is the aerial). Maybe it would make sense to earth the screen of co-ax cables concealed in walls rather than going down the RCD route, but none of the cable types permitted by 522.6.204 (i) are suitable for UHF.


    Or have I got completely the wrong end of the stick?

        - Andy.
  • 0
    I think you may have slightly got the wrong end of my stick there Graham, as indeed Andy has pointed out as well. What I was trying to say is that BS7671 should cover fixed electrical installations only, and restrict itself to mains or 110V ones, or perhaps some appliance connected SELV (eg. wander lead lights) as well. The equipment standards, cables, accessories are fine as they stand and should be referenced. Thus the electrical designer has one book about the electrical requirements. If we wish to add 12V for vehicles or boats, this needs to be separate, although some equipment like MCBs might end up the same. The energy saving measures are really nothing to do with the electrical design, although in some cases they may reflect on the way the design is carried out, and should be in the building regulations or other place where that can reflect the entire building design, not just the electrical parts. There is very little in BS7671 which relates to networks, AV, or other systems which happen to have fixed cabling, and certainly setting colour codes for alarm, telecom and AV cables is just plain daft. The place for the requirements on non-collapse during fires is the building regulations for example, then fibre cables are already included by using the words "nothing may be fixed with fixings which are not fireproof if they can cause danger to escape or access during a fire". False ceilings are then immediately included, and pipework and aircon and everything else. This is probably far too simple a system for some to understand, but is logical.


    As the BRs are under currently under review, it would seem to moving all these thing there would be a good idea. I realise that the BRs are statutory, and BS7671 not, but again this is not an impossible problem to manage. It would also make buildings safer, because serious non compliances would be criminal ofences which most of us would not wish to commit.


    Regards
  • 0
    David,


    I think you have missed my point.


    The interesting differentiator, is that the safety of SELV circuits and wiring for "power" is identical to that for most ICT, alarm, etc., applications - as are the "prevention of fire" and "reaction to fire" requirements, cable support/containment, and mechanical protection requirements..


    Therefore, it's best to have those in one place, surely, rather than repeating the requirements in other standards. That is why those standards


    Where they are different (SPDs for example), these are NOT repeated in BS 7671, and BS 7671 refers to other standards.

  • 0

    AJJewsbury:

    Thanks Graham - that's very useful.




    BS 6701 reinforces or augments BS 7671 requirements. There are no "conflicts". BS 6701 actually refers to BS 7671 as a requirement.



    That puzzles me - as I thought the only bi-colour allowed by BS 7671 for conductor identification was G/Y (for protective conductors) - so how does that sit with CW1308 etc cables with their bi-colour dots and backgrounds (I can't see how they comply with table 51, which seemingly 514.4.4 insists on) - indeed if you have a large enough cable pair 18 is green/yellow coded (if by dots rather than stripes) so and additional conflict with 514.4.2 there it seems. Likewise I don't think BS 7671 permits the blue core of my alarm cable to be used for anything other than "neutral". (It seems a bit in two minds over green as well.)

     




    BS7671 does not prohibit bi-colour conductors. It only puts a prohibition on the use of green-and-yellow. The only conductor functions specified in Table 51 are for power conductors, not telecomms ... in fact, 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. BS 7671 makes reference to requiring "augmentation" by other standards, which, by standards they reference, require the colours you are claiming BS 7671 prohibits - yet those conductors are not "line" conductors.

     


    Then as far as I can tell, an incoming BT line doesn't meet BS 7671's rather specific requirements for a SELV or PELV source (and presumably unlikely to give a ringer signal of up to 80V a.c.)  let alone many mains powered answering machines etc - so seemingly I must treat it fully as FELV if I'm to comply with BS 7671 chapter 41 - so I need cables insulated according to the voltage of the 'primary circuit' (mains?) and all exposed-conductive-parts earthed? Then, as you say, there's the 30mA RCD issue where the cables are concealed in walls.

     

    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?

     
    Similarly the TV, aerial amplifier, sat box etc don't obviously meet BS 7671 limited definitions of SELV/PELV sources (and several inject a d.c. voltage to power LNBs, masthead amps or remote control eyes, so we can't really presume the only power source is the aerial). Maybe it would make sense to earth the screen of co-ax cables concealed in walls rather than going down the RCD route, but none of the cable types permitted by 522.6.204 (i) are suitable for UHF.

    That may not be obvious, but see other parts of BS EN 60728, so RCD not required.


    In terms of earthing, a "distribution system" should be earthed ... this is covered in BS EN 60728-11, so for all those receiving perceptive (but probably "safe") shocks from their coax cables, or seeing small "sparks" when you unplug coax cables in dim light, consider this is the result of the fact that 0.5 mA "leakage" is permitted per appliance - if you think that your house may have a few TV sets or devices through which the coax passes, but then other devices are connected through coax, DVI, VGA, RGB, SCART, etc. and add all this "leakage" up, it perhaps gets to 1 mA "level of perception" current ... or exceeds it !

     
    Or have I got completely the wrong end of the stick?

        - Andy.

    Well, perhaps over-thinking some things, but all very valid questions.

  • 0

    Zoomup:

    It is all just too complicated and will deter future electricians from becoming interested in the industry. All these B.S. numbers and references and clauses are worse than the law. Wiring regulations should be simplified not made ever more convoluted and difficult to understand and apply. B.S. 7671 is like reading a blinkin difficult physics book these days. It has lost the plot, as has the I.E.T., BIG TIME.


    Z.




    Well, perhaps you have a point here.


    Even for domestic installations, the modern electrician may need to know about:

     - AV and entertainment systems, including various broadcast reception systems

     - Data and communications systems

     - HBES/BACS and other control and automation systems

     - Fire detection and alarm systems

     - Security detection/alarm, CCTV, access control systems

     - Power control and energy saving (we've been doing this through PIRs for a number of years)


    ... and this doesn't account for the "special locations" sections of BS 7671, along with the complexities of "prosumer's electrical installations".


    It's right to ask these questions, but blaming BS 7671 won't change the day job.

  • 0

    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.
  • 0

    Well, perhaps you have a point here.


    Even for domestic installations, the modern electrician may need to know about:

     - AV and entertainment systems, including various broadcast reception systems

     - Data and communications systems

     - HBES/BACS and other control and automation systems

     - Fire detection and alarm systems

     - Security detection/alarm, CCTV, access control systems

     - Power control and energy saving (we've been doing this through PIRs for a number of years)



    And how much would it cost an electrician to acquire a copy of all of the relevant standards? (along with the continual updates). There was a time when it seemed that the wiring regs references to other standards was only of relevance for selecting items of equipment - i.e. just check that the manufacturer provided assurance that it complied - and the regs told you everything you needed to know in terms of wiring it up. Now it seems we need to read dozens of other standards before we really know what BS 7671 means.


       - Andy.
  • 0
    Roughly translated "it`s a mess innit?"
  • 0
    BS7671:2018 appendix 1 has a listing of 19 pages of other standards it refers to. I doubt that your average sparky could tell you what a tenth of those BS's are about, let alone what their contents are.

Join us to get the best from IET EngX.

Joining EngX lets you personalise your experience so you stay up to date on the topics that interest you, plus you’ll be able to make connections who are looking to collaborate, exchange ideas and more.

Join us Not now

Community Rules & Guidelines