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multi-way cable & mains

Simon Hailes
Hi All,


Ref. wiring lights & a window opener in my conservatory;

This question mainly comes about because the window opener has three wires, neutral and two lives.  I've read a few posts about use of 'flex' for mains, but there is not much on use cable with 4 or more conductors.


I have:

An outside light (LED flood)

An inside light (5 mini-edison, currently LED)

A mains window opener ('up', 'down', 'common', 26W).


A 'control box' (set of relays connected to ESP8266 MCU, plus the 433mhz opener controller).

'switches' - a switch for each light, plus a biased switch for the opener.

The light switches will be in parallel with relays - so when switched off, the lights can be automated.

The opener switch will also be in parallel with 2 relays (and drives inputs to an opener controller).


The lights and opener could terminate up on an exposed beam near the light on the ceiling.  This would mean that I would only need 4 'live' wires plus neutral and GND (so 6 conductors minimum) between a junction box and the control box.

The cabling would be exposed (some may be in conduit).


For the switches, two would be switching live mains, and the biased switch would be switching two wires of undocumented 'control' (probably 12v dv) to a common ('signal gnd' of the opener controller?) (I will meter these and check exactly what voltages are involved).


The 'control box' will be powered from a plug, so the complete system can be isolated....


Questions:

1/ if connected to a plug, is this covered by part-p?


2/ I'd like to minimise the wiring to keep it pretty.  From the junction box to control box:

I could (for economy) go with a pair of 3-core+earth, or I could go with a 6 core multi-way cable.  Or I could go with 3 x 3 core cables, treating each device as separate.

But whatever I do, the colours of the cables will not completely represent their function - e.g. if using 3 core flex for the opener, then the earth would be used for neutral, and that seem very BAD to me.

So I like the idea of a multi-core better, if only because at least I may be able to make neutral blue and earth green, and the other colours NOT being standard will at least make someone in the future think twice...

When looking at available multi-core cable, (e.g. on CPC), most is quoted as 'control' even though rated good enough for what I need (1mm sq, 300v?), is this just because it's not std colours?

Comments and thoughts appreciated :).


3/ I'd like to minimise the wiring to keep it pretty (2).  From the control box to the switches:

Since the biased switch is assumed to be DC (and I probably can't get a biased switch which will fit in a 'normal' domestic switch arrangement), I'm thinking that it's wise to run separate wiring for the switching of live for the lights and the DC switching.  Am I right to think it's not good to run them in the same multi-core cable, or just paranoid?

I'd like to use black flex for the mains switches.  I assume 4 core would be ok - live + two switched live + earth?  Is colour important if all wires are sleeved red at the switch?


thanks in advance for any thoughts...


Simon
  • 0
    it is covered by part P,  all of domestic wiring is, but unless you live in Wales, it is not notifiable, unless within the  60cm zone 2  of a bath or shower, or so complex as to require the creation of a whole new circuit back to the board, or the replacement of a consumer unit.


    Any colour that cannot be mistaken for the earth can be used as live, so long as there is an indicator in the form of a length of  sleeve or flag of tape  in Brown at both ends  (Not red please, it is only 15years since the colours changed over)

    300V control  cables carrying 230V AC are fine, but are only supposed to be used downstream of suitable ADS - not an issue in your case.
  • 0
    Not complete and in no particular order...

     

    1/ if connected to a plug, is this covered by part-p?



    Technically the plug & socket makes no difference - if your wiring is "fixed" then it's covered by part P - although it doesn't sound in your case that it would be notifiable.

     

    (and I probably can't get a biased switch which will fit in a 'normal' domestic switch arrangement)



    Actually "2-way, retractive, centre-off" switches are readily available - usually as 'grid' modules that are assembled into what looks not unlike a typical lightswitch.

     

    But whatever I do, the colours of the cables will not completely represent their function - e.g. if using 3 core flex for the opener, then the earth would be used for neutral, and that seem very BAD to me.



    This is a common situation - and the usual solution is to identify each wire at both ends correctly by means of a short length of sleeving of the correct colour - you'll often see a blue (or black in old colours) wire at light switches oversleeved in brown (or red). Technically oversleeving G/Y in a multicore cable is permitted  - but is hardly ever done since the regulations require that an earth is provided at every point and accessory in domestics - so normally the G/Y wire is used as earth. This requirement applies even if the items are double-insulated as it allows for future replacement with items that require an earth.

     

    Since the biased switch is assumed to be DC (and I probably can't get a biased switch which will fit in a 'normal' domestic switch arrangement), I'm thinking that it's wise to run separate wiring for the switching of live for the lights and the DC switching.  Am I right to think it's not good to run them in the same multi-core cable, or just paranoid?



    It rather depends on the system the switches are connected to - not just the voltage but the associated means of protecting against electric shock. Some "functional extra-low-voltage" (FELV) systems need to be treated pretty much as mains (mains voltage insulation) etc. because under some fault conditions (e.g. short in a transformer) they could reach a lethal voltage. Others (e.g. SELV) are pretty much guaranteed not to become hazardous in themselves, but then their wiring needs to be kept (electrically) well away from mains so that remains the case. Manufacturer's installation instructions should be able to point you in the right direction, but failing that wiring it as if it were mains but keeping it separate from any real mains seems like a sensible approach.

     

    When looking at available multi-core cable, (e.g. on CPC), most is quoted as 'control' even though rated good enough for what I need (1mm sq, 300v?), is this just because it's not std colours?



    Ah, if you're looking at YY/CY/SY type cables, that's a long an on-going discussion. It basically boils down to the problem that they're not (entirely) in conformance with any British or European standard (but sometimes a German national one) - which can make demonstrating that they meet wiring regs requirements tricky.

     

    Is colour important if all wires are sleeved red at the switch?



    Core colour can be ignored if oversleeved - but the correct colour for line for fixed wiring is brown, not red, these days (since about 2005).



      - Andy.
  • 0
    thank you both for really good info.


    So, after writing I went looking in more detail at multi-core cables, and it seems that if I want to comply with BS 7671, *could* use YY, but only if:

    The Mfg states compatibility with *some* national or international or standard.

    The standard can be show to have equivalence to standards quoted in BS7671 for the use it's being put to.

    That the installer documents why and how the standard quoted is equivalent.


    So, I am tempted to specify 2 x 3 core+earth for junction box to control box, and the same for control to switches, just because something like 3184Y *is* in BS7671?

    Am I right to think that one can asily get 4 core which complies, and that >5 core which natively complies would be much more difficult to obtain?


    So something like 
    Yellow/Green

    Blue

    Brown

    Black


    (http://www.caledonian-cables.co.uk/products/fireproof/fireguard/pvc-pvc-powercable.shtml)

    would just be easier than trying for a higher number of cores :).


    br,

    s


  • 0
    You can get many cored flex to UK and/or EN standards - e.g. https://uk.rs-online.com/web/p/electrical-mains-power-cables/7756173/ 


    Conventionally though, rigid cabling is preferred for fixed wiring (not least because it's cheaper and readily available). It's quite normal to run two or three cables alongside each other to get the required number of cores (say a twin & earth and a triple & earth if you need five current-carrying cores) - the only bit to be careful about is when running them though holes in steel enclosures (e.g. knock-outs in flush boxes) that the currents in all the cores though each hole 'sum to zero' - so L & N, or L and all associated switched Ls, though the same hole.


    If prefer not to use T&E then maybe look at BS 8436 (nailshield) cables - they're readily available in anything up to 4 cores + earth (and some places online will sell you cut lengths too) and the aluminium screen might provide some extra reassurance for the separation between LV and ELV circuits.


      - Andy.
  • 0
    you see a lot of   This sort of 5 plus earth core flex  in heating systems. Perfectly OK for fixed wiring, and easier to terminate in small terminals.


     same sort of thing, with per meter pricing. 

    Personally I prefer not to run mains and 12V or whatever in the same cable, even if the route is the same - it makes mistakes less likely.
  • 0
    With ref to the oversleeving... I am of the (controversial) opinion that brown/black/grey are all phase colours, and do not need oversleeving. (I DID oversleeve the blue back before 2005, because of the possibility of confusion with a neutral)...


    Why do brits always think live should be brown? The existence of 3 phases is not a mystery to most?
  • 0

    MHRestorations:

    With ref to the oversleeving... I am of the (controversial) opinion that brown/black/grey are all phase colours, and do not need oversleeving. (I DID oversleeve the blue back before 2005, because of the possibility of confusion with a neutral)...


    Why do brits always think live should be brown? The existence of 3 phases is not a mystery to most?




    So there I was today putting my brown sleeves over the black and grey conductors on some two-way switching; as well as, of course, the blue of the T&E of the switch drop.


    It doesn't take any effort, but I think that MHR has a very good point. ?

  • 0

    With ref to the oversleeving... I am of the (controversial) opinion that brown/black/grey are all phase colours, and do not need oversleeving.



    But by the letter of the regulations, black and grey don't just identify any old line (phase) conductor, but specifically line 2 and line 3 of a 3-phase system - which of course in this case they are not.


    That's not to say I don't have some sympathy for the idea - the French approach of regarding any colour other than blue or green/yellow as line in some ways makes life an awful lot easier (especially in conduit systems - popular in their domestics). Imagine wiring a switch where you could immediately tell from the core colours which were the permanent lives, which was the switch live, and which were the strappers, all without having to mark anything during drawing in, or bell out, or oversleeving. A much more "workman-like" approach IMO.


    I do leave black unsleeved as a smoke detector interconnect line - as that's a valid colour for control & signalling circuits by table 51.


      - Andy.

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