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Using mains cable for control wiring, what about colour coding, and then a question about armour

Will D

Hello everyone,

Two questions for a personal project:

1.

I'd like to run some extra cable between my house and our heat pump for possible future use for controlling 3-way valves. My understanding is that BS7671 asks for 3-core control wire to have the neutral/mid-wire be blue, and the other two wires to be one of a range, but not yellow/green like an earth wire. Our heat pump asks for these wires to be 0.75mm2 CSA and as they're for mains voltage they'll have a suitable voltage rating too. However, I've searched around and can't find any 3-core cable which complies with all of these requirements.

The main sticking point is the colour-coding. I can only find 3-core cable in either standard mains colour-coding (brown, blue, yellow/green) or in 2x black and 1x yellow/green. I thought of running a cable with many cores, as I need to run a bunch of 2-core as well for other possible future uses, however all the multi-core I can find also follows the black+yellow/green coding. I can't find any suitable 3 or multi-core wire that has any blue cores!

So, I was wondering what's acceptable, or what's the common practice. Just use either the mains or the black+yellow/green multi-core wire and sleeve it to make it clear what's doing what? Or do I not need to do anything at all?

For reference, the existing wiring from the install done a year+ ago uses a black+yellow/green multicore to run out from the wiring centre to the heat pump, and mains-coloured 3-core inside the house from the wiring centre to the connection box with the 3-way DHW valve. This suggests to me that black+yellow/green multicore is acceptable without sleeving, however it's the fact that BS7671 seems to ask for a blue core which has me bamboozled.

2.

As said, the cables need to run out from the house to the heat pump, it's about 7m total with about 1m actually underground. The cables are in trunking the whole way, even when underground. I don't think the existing cabling has armour, so I wasn't going to buy armoured cable for these new runs, but as I was already writing a question I thought I'd ask about this too.

3. ;)

Not a question, but for complete info I also need to run a 5-core cable for connection of the heat pump's wired controller which will follow the same route. It doesn't need 0.75mm2 and doesn't carry mains voltage. The heat pump manufacturer told me that it doesn't need to be screened/shielded and even Cat6 cable would be fine. I was just going to buy a 5-core multicore cable for this.

Cheers Slight smile

Parents
  • 0

    0.75mm heat resistant  5 core flex is brown/blue/green&yellow/black and grey if that's any help.

    Gary

  • 0 in reply to Will D

    Would H05RN-F do the job. Oversleeve the live conductors and use G/Y if required.

  • 0 in reply to Will D

    I find it pretty bamboozling that BS 7671 can prescribe a certain colour coding but that colour-coding isn't really available to buy - how can anyone expect electricians to follow the code if the materials aren't available?

    Generally manufactured cable colours do match BS 7671 - but on the assumption the cable is used in one particular way - usually the assumption for 3/4/5-core cables is that it's for 3-phase - hence brown/black/grey/blue/G+Y cores. Very often thought the application is different - e.g. using 3-core + c.p.c on single phase lighting circuits, so oversleeving the ends becomes the norm - there being just too many combinations (three L, two L and one N, etc) to make manufacturing different versions economic. Beyond 5 cores, as you've seen it's all black (with numbers) plus G/Y.

       - Andy.

  • 0 in reply to AJJewsbury

    Beyond 5 cores, as you've seen it's all black (with numbers) plus G/Y.

    Well except in a few cases when it isn't ;) 

    Superlec cables supply the following multicore mains cables for use in central heating systems etc and claim they meet an impressive bundle of British standards.

    Core IDs

    • 2 Core: Brown Blue
    • 3 Core: Brown, Blue, Green/Yellow
    • 4 Core: Brown, Black, Grey, Green/Yellow
    • 5 Core: Brown, Black, Grey, Blue, Green/Yellow
    • 6 Core: Brown, Black, Blue, Red, White, Green/Yellow
    • 7 Core: Centre: White, Surrounded by: Brown, Black, Green, Blue, Red, Yellow

    That last one has no green yellow core anyway !  

    In practice while it would be nice to always follow the letter of the standards, I don't think anyone will mind what colours you use, and the electrons certainly won't.  so long as you don't misuse green and yellow, and whatever is done, please label or  record it somewhere for the next person in, or if your memory is as good as mine, for your future self.

    Mike.

  • 0 in reply to mapj1
    mapj1 said:
    Superlec cables supply the following multicore mains cables for use in central heating systems etc and claim they meet an impressive bundle of British standards.

    Yes, but: "318*B zero halogen flexible cord cables are used as an indoor general wiring cable" [my emphasis]

    Will D said:
    when I've found that cable it says not suitable for outdoor use

  • 0 in reply to Chris Pearson

    yes sorry I was more responding to the comment about black cores for 5 and above.

    At this rate he'll be driven to installing singles in flexible conduit instead.

    Mike.

  • 0 in reply to Will D
    Will D said:
    I find it pretty bamboozling that BS 7671 can prescribe a certain colour coding but that colour-coding isn't really available to buy - how can anyone expect electricians to follow the code if the materials aren't available?

    I'm not sure I understand, for the following reasons:

    • BS 7671 only requires colour to be at terminations (and only preferably throughout its length), so sleeving can be used.
    • BS 7671 also permits identification by alphanumeric marking (letters and/or numbers), again at terminations.
  • 0 in reply to Chris Pearson

     My difficulty was finding 3 core cable suitable for control wiring for a 3-way valve, one neutral and two live conductors, which would comply with BS 7671 where the neutral should be blue and the others permitted to be a range of other colours but not yellow/green. That cable you referenced is 3-core but one of the cores is yellow/green so can't be used in the application I'm considering.

  • 0 in reply to AJJewsbury

     yes I can see that it's not possible to make all possible permutations, I'm just surprised that a 3-core cable which follows the colour coding for control wiring isn't readily available, but maybe it's just not used often enough to make it worthwhile producing.

  • 0 in reply to mapj1
    mapj1 said:

    At this rate he'll be driven to installing singles in flexible conduit instead.

    Mike.

    Now that's an idea...! :D

  • 0 in reply to gkenyon

     then why aren't all cables just black multicore with a yellow/green for earth? Yes sleeving is allowed, but it's not preferred if the right colour cores are readily available is it? 

    Anyway, in this case I can't find the cable with cores in the right colours, so I'll have to use sleeving anyway.... and to be compliant with both BS 7671 and BS EN 60204-1 I should use blue and red sleeving on the neutral and red and one other colour on the live conductors.... but I think that's probably getting a bit silly.

Reply
  • 0 in reply to gkenyon

     then why aren't all cables just black multicore with a yellow/green for earth? Yes sleeving is allowed, but it's not preferred if the right colour cores are readily available is it? 

    Anyway, in this case I can't find the cable with cores in the right colours, so I'll have to use sleeving anyway.... and to be compliant with both BS 7671 and BS EN 60204-1 I should use blue and red sleeving on the neutral and red and one other colour on the live conductors.... but I think that's probably getting a bit silly.

Children
  • 0 in reply to Will D
    Will D said:
    then why aren't all cables just black multicore with a yellow/green for earth? Yes sleeving is allowed, but it's not preferred if the right colour cores are readily available is it? 

    That is more complicated, but is to do with harmonization originally agreed in the late 1960s by and for international cable manufacturers.

    We're rather late to the party on that one - it happened before I was born !

  • 0 in reply to Will D
    Will D said:
    Anyway, in this case I can't find the cable with cores in the right colours,

    There is a reason for that ... power cables with flexible conductors and up to 5 cores, with core identification by colour, are affected by European harmonisation that goes back to the late 1960s. Other power cables with up to 5 cores will be manufactured to align with the national wiring standard for power circuits (in the EU and UK these align with BS EN IEC 60445, but there are variations of the line conductors, for example UK and Ireland these are BN, BK, GY, but some countries use BN, BK, BK)

  • 0 in reply to gkenyon

    I will admit that I'm starting to get a bit lost with all the standards, variations, possibilities. However, maybe going back to the root of my original question, which is why the wiring regs say that for control the colour of the neutral or mid-wire must be blue:

    electrical.theiet.org/.../bs-7671-2018-corrigendum-dec-2018-v2.pdf

    I've referenced a free corrigendum because 1) I don't actually have a copy of the wiring regs to reference and 2) the corrigendum is freely available for anyone to access.

    I appreciate that in most 2-wire control cases a simple L+N brown+blue 2-core cable will suffice. In my case I'm looking for a 3-core cable for control of a 3-way valve, which in a domestic setting isn't that unusual for a heating system. If this is a fairly common type of cable-need, then why can't I easily find this kind of cable in the UK? I appreciate that there may be another standard for colour-coding of 3-way valves for heating systems which I'm not aware of (just as I wasn't aware that BS EN 60204-1 would apply to external wiring for a domestic heating pump). However, if I've not missed something, then why can't I find this cable which surely must be needed in lots of situations in the UK? Maybe the answer is just that it's not needed frequently enough to justify the existence of a specific cable.

    Or, maybe 3-way valves were never the intended purpose for the colour-coding for control wiring in the wiring regs? If that's the case, then what does it mean by "mid-wire"?

  • 0 in reply to Will D
    Will D said:
    then what does it mean by "mid-wire"?

    It's to cover "neutral like" cases in some less common supply arrangements, e.g. the "M" wire in this diagram (from BS 7671 section 3 - the "coils" represent supply transformers):


       If this is a fairly common type of cable-need, then why can't I easily find this kind of cable in the UK?

    Oversleeving the ends is the usual solution. The only case I can think of where "special" core colours are available is for "twin brown" T&E - used for switch drops - but even then the vast majority of installations still use brown/blue and oversleeve the blue with brown sleeving. It's just easier to have one reel of cable and use it for everything - and it's normally significantly cheaper too (because the way the wholesale system works higher volumes mean lower prices).

    Also once you get two or more cores the same colour it becomes difficult to work out which is which (brown and black oversleeved brown are immediately distinct at both ends - whereas two browns means you'd have to get a meter out and start continuity testing or have numbers printed on each core to be able to connect them correctly (other then in the simple switch drop case where it doesn't matter if they're reversed). Which is probably why you don't get 3-core all brown - even though the vast majority of 1.0 or 1.5mm² 6243Y is used for two-way switching on single phase lighting circuits.

       - Andy.

      

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