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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
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  • 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.
Reply
  • 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.
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