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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 aligarjon

    Thanks  unfortunately when I've found that cable it says not suitable for outdoor use.

    I think I'm just going to use multicore black+green/yellow and tape or sleeve the ends according to usage.

    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?

    Cheers Slight smile

  • 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.

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  • 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.

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