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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

  • 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.

  • 0 in reply to mapj1
    mapj1 said:

    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.

    I think that this is the answer - a wiring diagram with wire colours written on them, together with wiring labels and colour sleeves.

  • 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

    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.

    SWA would be the usual choice for outdoors/underground.  You could use 3-core, oversleeve black with brown as your 2nd L and grey with blue as N and use the armour as the c.p.c.Or four-core (which has a blue core) and oversleeve for 2nd L and c.p.c. or 5 core which usually gives you a blue and G/Y cores (plus a spare core for future expansion). (The armour still needs earthing at at least one end whatever).

       - Andy.

  • 0 in reply to AJJewsbury

    Thanks for the suggestion , as sleeving is required anyway it seems that the core colours aren't really important so I might as just buy the most economical cable that meets other specs. I agree that SWA is what's needed for direct burial but in this case the cable runs through a duct for the short section when it's underground so I don't think the SWA is needed.

  • 0 in reply to AJJewsbury

    Save that Will D specified 0.75 mm² and I think that the minimum size for SWA IS 1.5 MM², so it would be necessary to ensure that it would fit the terminals.

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