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Discuss Adding class I fittings to lighting circuit / extending cpc in the DIY Electrical Forum area at ElectrciansForums.co.uk.

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  1. jufjuf0
    Offline

    jufjuf0 DIY

    Location:
    Huddersfield
    Hi All, I'm a DIYer after advice please.

    All the lights in my house (ground floor and upstairs) are on one circuit - old colours, as you might expect with the age of house (120 years).
    There is a cpc (earth) from the (modern) consumer unit to junction boxes on both floors of the house - verified as less than 1 ohm.
    However, that's as far as it goes - the actual fittings (switches and luminaires) are not connected to cpc - they are mostly run in single core.

    I'm led to believe that this is okay, providing that the fittings are class II / double insulated / plastic which nearly all of them are. The one metal dimmer switch can easily be replaced with a plastic one.

    The issue I have is that we'd like to install metal (class I) light fittings in two upstairs bedrooms. It wouldn't be too tricky to connect them to cpc from junction box, which comes from consumer unit.

    What I am not clear about is: would it be adequate to just earth the two class I fittings by extending the cpc from junction box and leave the rest of the installation as is, or;
    by introducing class I fittings to the lighting circuit, do all the switches and luminaires on that circuit then also need a cpc connection, regardless of which class they are
    ?


    • As a DIYer, can I carry out this work or do regulations mean I need to get electrician to do this?
    • Would it be wise to consider updating the system anyway e.g. separate lighting circuits for separate floors? Again, if so, can I do this, or does it need to be done and/or certified by a professional?
    • Perhaps I should forget the new class I fittings and just get class II light fittings and leave the wiring as is(?).
    This last option is easiest on one front, but more tricky to persuade my wife to move away from the carefully chosen pretty fittings!

    Your expert opinions welcome. Would be good to at least consider my options before getting an electrician in to have a look.

    Thanks.
     
  2. telectrix
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    telectrix Scouser and Proud of It Trusted Advisor

    Location:
    cheshire/staffordshire
    Business Name:
    Telectrix
    you could do as you suggest. run a cpc from the JB to the classI fittings (and any classI switches). this should 4mm single cable if not mechanically protected. It would be a better idea to rewire the lights as 2 separate circuits. this would require a professional electrician who can test and certify the work. earthing and bonding would need to be tested for compliance and brought up to standard if not already satisfactory.
     
  3. Spoon
    Online

    Spoon Trusted Advisor

    Location:
    Lancashire
    Hi mate.

    It can be hard changing the minds of women, but its all about safety. My missus had it in her head that these stupid 'safety socket covers' were a good idea. I showed her that they weren't and how the kids could end up getting hurt, then binned the lot. Tell the missus that putting metal fittings onto a circuit that doesn't have a CPC is a bad idea and someone may end up getting hurt or killed.
    What size cable is the earth cables going to the junction boxes and is it in conduit, ducting or trunking? The reason I ask is there is a regulation about cable sizes and installation methods.
    When was the modern CU installed? I take it the existing cables were checked at the same time of the CU change? Was the CU change done my an electrician & do you have a certificate of the change?
     
  4. jufjuf0
    Offline

    jufjuf0 DIY

    Location:
    Huddersfield
    Thanks for quick responses Spoon/telectrix.

    Truth be known, I actually quite like the class I fittings too, so have to consider them rather than conveniently blaming the missus entirely!

    The CPC to the junction boxes is part of the 1mm[SUP]2[/SUP] T+E cable so runs the same route as live and neutral (i.e. in conduit within walls for verticals between floors, but otherwise laid loose under floor boards or clipped to walls).

    Does the non-mechanically-protected CPC need to be so thick as 4mm if it follows the same route as live+neutral or does it have to be 4mm only when run separately?

    As relatively recent new owner of house, I know little of its history. The previous owners passed on no documentation whatsoever (they emigrated and weren't interested in certificates for anything).
    From electrician's pre-purchase inspection and what I've uncovered, I'd describe the wiring as generally old but not especially dodgy. I guess that the CU has been fitted within the last 20 years (pic attached), likely by an electrician, but no known certificate.
    ConsumerUnit.JPG
    I'm thinking of replacing the single core cables that run to where the metal light fittings will be with T+E, and connecting CPC at JB.
    Later on, perhaps when doing an extension to the house/building into attic, might be a good opportunity to seek professional advice and split the two floors' lighting circuits onto separate breakers at the CU.
     
  5. telectrix
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    telectrix Scouser and Proud of It Trusted Advisor

    Location:
    cheshire/staffordshire
    Business Name:
    Telectrix
    my comment re 4.0mm above.
     
  6. Spoon
    Online

    Spoon Trusted Advisor

    Location:
    Lancashire
    If you are going to do this then couldnt you just do it for all the lights upstairs and then if you want any fitting changing in any other rooms everything will be ok?
     
  7. telectrix
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    telectrix Scouser and Proud of It Trusted Advisor

    Location:
    cheshire/staffordshire
    Business Name:
    Telectrix
    if using T/E from JB to fittings, then you won't need to use 4mm. the cpc in the T/E will suffice as it's sheathed.
     
  8. jufjuf0
    Offline

    jufjuf0 DIY

    Location:
    Huddersfield
    Thanks both.

    @telectrix: BS7671 543 has proved to be as good a read as expected. It details a lot about cpc size requirements when using a separate conductor but I was struggling to find much about cpcs as part of a cable along with live/neutral conductors. Glad you clarified what I was thinking - i.e. that the integral cpc of the T+E would be adequate (couldn't see the point in it being there if not).

    @Spoon: Yes, I was considering doing all the upstairs lights, but will start with the two I know will have class I fittings first. Hope the pretty fittings are worth the effort!
     
  9. Spoon
    Online

    Spoon Trusted Advisor

    Location:
    Lancashire
    I know I'm probably stating the obvious but: When you are updating the wiring, if there is no cpc in the switch wire then make sure the missus doesn't change any light switches to metal.
    I presume it that you are only updating the power to the lights and not the switch wire.
     
  10. jufjuf0
    Offline

    jufjuf0 DIY

    Location:
    Huddersfield
    Better to state obvious than for something basic go badly wrong.
    You're right - the switch wire will still (for now) have no cpc but we've already had the conversation and agreed to plastic switches until professional re-wire done further down the line.
    Thanks.
     
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