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 2134 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.
Parents
  • 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.

Reply
  • 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.

Children
No Data

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