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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

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  • 0
    Will D said:
    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.

    I believe heat pumps, like HVAC systems, are classed as Machinery as defined in the Supply of Machinery (Safety) Regulations.

    In this case, the controls (auxiliary circuits) would come under BS EN 60204-1, and not BS 7671. The standard has different colours for controls than BS 7671.

  • 0 in reply to gkenyon

    Hi  , that's interesting, I had thought that the distinction only applied if the wiring is inside a cabinet. These cables will be run between the house and the heat pump and will be in a domestic setting, so I want to make it easy for general electricians to know what they're looking at, as many might not be familiar with BS EN 60204-1, would they?

    Cheers Slight smile

  • 0 in reply to Will D

    No, the controls, and interconnections, form part of the 'machinery' system. The demarcation is the point of connection of mains supplies from separate circuits in the installation - the controls are from one part of the machinery (controls) to another (actuator etc.).

    The heat pump system, and valves, separately and collectively, are 'machinery'.

    That does not mean BS 7671 is totally ignored, and it would be recommended to meet the requirements of both standards, where practicable.

    Since the requirement of BS EN 60204-1 for colour coding are for the safety of those working on the 'machinery', I would follow that standard, but for fire safety, cable supports etc., I would follow BS 7671 if those requirements are more onerous.

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  • 0 in reply to Will D

    No, the controls, and interconnections, form part of the 'machinery' system. The demarcation is the point of connection of mains supplies from separate circuits in the installation - the controls are from one part of the machinery (controls) to another (actuator etc.).

    The heat pump system, and valves, separately and collectively, are 'machinery'.

    That does not mean BS 7671 is totally ignored, and it would be recommended to meet the requirements of both standards, where practicable.

    Since the requirement of BS EN 60204-1 for colour coding are for the safety of those working on the 'machinery', I would follow that standard, but for fire safety, cable supports etc., I would follow BS 7671 if those requirements are more onerous.

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  • 0 in reply to gkenyon

    Thanks for clarifying, that's helpful.

    Unfortunately, I have not yet found multicore cable in BS EN 60204-1 colours either - red for AC control, at least, as I understand the coding. Lots of black cores with a spattering of yellow/green cores is plentiful and is what was used by the heat pump installer originally, but multicore which complies with either BS 7671 control wiring or BS EN 60204-1 AC/ or DC control wiring seems to be very rare. I bet if I do find it it will be cost prohibitive for a small personal project and is probably why it wasn't used in the first place.

  • 0 in reply to Will D
    Will D said:
    Unfortunately, I have not yet found multicore cable in BS EN 60204-1 colours either - red for AC control, at least, as I understand the coding.

    Agreed ... you won't necessarily find 'power' cables that are so identified. Broadly, for 'power' functions, at least AC, BS EN 60204-1 aligns with BS 7671 (the term 'light blue' is used for neutral). 

    Many auxiliary cables used for this function will be alphanumeric numbered (e.g. SY, CY and YY cables). BS EN 60204-1 permits this. Coloured sleeving can also be applied.

    Other auxiliary cables are available.

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