RCD for bathroom lights??

Discussion in 'Electricians' Talk' started by Oo_phoenix_oO, Feb 12, 2014.

  1. Caddy

    Caddy Active Member


    You more then likely have whats known as a "borrowed Neutral" What usually happens is the Neutral for the upstairs lights is used to power the landing light which gets its live supply from the downstairs lights, or Vis Versa.. Now things are perhaps getting a little tricky to sort out, in that you shouldnt have a borrowed neutral from one circuit to another and should really be rectified.

    Moving both circuits onto the RCD will stop it from happening but now you have all your lights and sockets on the RCD which again isn't advisable and technically against the regulation of minimising inconvenience in the event of a fault.. and you still have the problem with the borrowed neutral.

    Unfortunately this is a perfect example of a simple job turning into a nightmare..

    2 options, 1 move them both over and leave it, 2 get someone in to take a look at correcting it properly but this could lead into alterations to lighting circuit to correctly seperate them from one another and depending on what is involved with that and the age of your board, A new board to give separate RCD protection on the altered lighting circuits If they need to put new cables back down any walls.
    FatHands likes this.
  2. seneca

    seneca Screwfix Select

    It sounds like you have a shared neutral somewhere, easiest way around that would be to put all lights on the same circuit on the rcd side of the board. Do not put the lights up & down on separate breakers on the rcd side!
    FatHands likes this.
  3. Oo_phoenix_oO

    Oo_phoenix_oO New Member

    Oh dear, thank you for taking the time to explain, I think ultimately I need to get it sorted incase I have the friendly neighbourhood B.c officer come round after the bathroom is done, but for now, I think I will move both rings onto the rcd rather than move it back to whense it came, is there any saftey reason why these can't all be on the rcd side of the cu, why wound,nt the spark who fitted it put everything on the rcd side, is it just because lights are static and thus safe?

    Thank you again for taking the time to respond.
  4. seneca

    seneca Screwfix Select

    Until the 17th. edition came in it was only sockets that were rcd protected. When 17th. arrived cables buried in walls needed rcd protection hence lighting circuits then became involved. As I said earlier, if you decide to put all lights on the rcd side, also put them all on the same breaker, this is for the safety of anyone working on the lighting circuits.
    FatHands likes this.
  5. Oo_phoenix_oO

    Oo_phoenix_oO New Member

    Thank you Seneca and Caddy,

    So if I move the both circuits to the rcd side, I would also be better off putting them into the same mcb (putting two sets wires in the same mcb rather than have two mcb's one for up and one for down stairs), ideally I would just like to move both up and down onto the rcd and leave
    It at that, all good :), I work I'n IT, I hate paying for something you can do yourself, however safety first, would rather the family safe than save a few quid :)
  6. seneca

    seneca Screwfix Select

    Yes put them all on the same mcb. The reason being that if they're on separate mcb's and someone turns off one of the mcb's to carry out work, current can come back down the neutral from the other circuits mcb! Not sure if I've explained that very well but please take my word for it. It is quite common to find the shared neutral situation, very often on consumer unit changes and usually in my experience on '80's built houses. Doing what I've suggested is often the only practicable option.
    FatHands likes this.
  7. Oo_phoenix_oO

    Oo_phoenix_oO New Member

    Thank you, I think the house was rewired in 88, I only moved in last July so still making it our own, and still on a learning curve, as to what the b.c officer is happy with (forgive me but it all seems a bit jobs worthy like all health and safety stuff now), I will take take the advise offered and do as suggested, I'm only going to get b.c involved when necessary, but want to make sure everyone is safe, thanks to all again, and if ever in need of IT support, don't go pc world, ask an expert like yourselves and save a few quid, for those who arn't willing to share their knowledge, charge the earth :)
  8. Oo_phoenix_oO

    Oo_phoenix_oO New Member

    One final thought, both the mcb for the light circuits are 5a, if I put both light circuits into the same mcb, would I need to change it to a higher rating?.

    Thank you again for time.
  9. seneca

    seneca Screwfix Select

    Most likely not although it does of course depend on how many lights you have! 5amps will accommodate over 1kW of lighting so I doubt you have more than that and of course they won't all be on together, I've done this lot's of times on consumer unit changes and never had any problems.
    FatHands likes this.
  10. Risteard

    Risteard Well-Known Member

    Amendment 2 (BS 7671:2008 (2013)) was for a new Section 722 Electric Vehicle Charging Points.

    It was Amendment 1 (BS 7671:2008 (2011)) which excluded SELV (although presumably this was intended with the publication of BS 7671:2008 initially).
  11. Oo_phoenix_oO

    Oo_phoenix_oO New Member

    Thank you. All sorted, working with no problems. Although is what I have done with the terminal blocks ok?, they are 6a strips. The wires would not reach :(. The third wire going in the mcb is for the door bell it would seem.

    Attached Files:

  12. Risteard

    Risteard Well-Known Member

    I can see exposed copper. Also never heard of 6A block connectors - presumably you mean 5A?

    And what is that insulating tape doing on one of the cores?
  13. Oo_phoenix_oO

    Oo_phoenix_oO New Member

    The tape was just while I was following it tryin to untangle it. I will trim the end down so no copper is showing. The strips were from screwfix.
    Thank you.

    Attached Files:

  14. wally

    wally Screwfix Select

    Sounds like a borrowed neutral but if it was rewired in 1988 as you think that practice went out many years before that so sounds like the original sparky was well out of date wit his knowledge
  15. spinlondon

    spinlondon Well-Known Member

    Sounds like you have a shared neutral.
    So yes moving both of the lighting circuits over to the RCD side would prevent the RCD from tripping (unless there's a fault of course).
    Not notifiable, unless the work is within the zones.

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