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1. Lighting circuit safe area, does it need RCD? 2. RCD maximum current smaller than combined rings

Discussion in 'Electrics UK' started by TofuSpaceship, 27 Feb 2020.

  1. TofuSpaceship

    TofuSpaceship

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    Looking at that eyesore of our CU, I noticed that the RCD (which protects only kitchen, upstairs and downstairs rings) is rated for 60A when the circuit breakers are 32a each. Is that a problem? I am aware that it is unrealistic to have 3*32A=96A at any given moment, but it is theoretically possible.
    What would happen to the RCD in that instance? Does it get damaged, or will it simply trip when the combined load on the three rings go over the 60A?

    Secondly, all of our lighting circuits, cooker, fridge and boiler are on the CU section w/o RCD.
    I am a bit surprised as I just stumbled somewhere on the net saying that if a lighting circuit is buried less than 5cm into a wall, it needs RCD.
    We just had our kitchen done and the leccy hasn't brought up that point and our wiring are definitely within 5 cms of the walls (if anything, there's cables going down to our new switches); they are within the safe areas though, as I could observe during installation.
    Is the fact that the wiring sits in the safe areas trumping the need for RCD?
    What about cooker and boiler? Wiring for these also sits in the safe areas.

    If it helps with regs, our installation is 20ish year old by the look of it.
     
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  3. Taylortwocities

    Taylortwocities

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    The 50mm wiring needing an RCD is a relatively recent regulation. Regs are not retrospective, but any new work that the leccy did must comply. So new wiring to the new switches should be on an RCD protected circuit.

    He should have given you a certificate that says his work complies with BS7671. Did you get one?

    Don't worry about the 60A RCD v 3x32A. Thats all standard stuff.
     
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  4. AndyPRK

    AndyPRK

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    and no the RCD won't trip over 60A
     
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  5. TofuSpaceship

    TofuSpaceship

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    so what does the RCD rating of 60A stands for? I am one who likes to understand things rather than just being told it's OK and I can sleep tight at night.

    I haven't got a paper from the leccy. I will check with my partner if she has any idea about it.
    Alas the leccy came with the builder so we didn't have much direct contact with himself
     
  6. Taylortwocities

    Taylortwocities

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    The 60A refers to the maximum current that the RCD’s contacts are rated at. The RCD does not trip when handling a current of 60A. An RCD does not protect if there is over current, it trips if there is an earth fault of 30mA or more.
    Google RCD and also MCB to understand what they both do for a living.

    it doesn’t matter that the electrician worked for the builder. All electrical work should have an installation certificate. It tells you the test results for the work (we are hoping he tested it) abc that the work complies with BS7671. there’s more paperwork to expect if he installed any brand NEW circuits. Did he?
     
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  7. TofuSpaceship

    TofuSpaceship

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    Hey @Taylortwocities thanks for the explanation. I am aware an RCD protects only in case of residual current mismatch and not over load.
    Does it mean that if the RCD contacts are rated at 60A, they are potentially at risk, seeing that the 3 rings can each go up to 32A before the circuit is opened by the circuit breaker?
     
  8. AndyPRK

    AndyPRK

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    Your main house fuse may only be 60A
     
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  9. Taylortwocities

    Taylortwocities

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    If your three rings get anywhere near 60A you have a real problem. Circuit design means that 96amps can’t happen.
    If that were a possibility, we would need a nuclear power station for every town.

    Have a think about what you would need to plug in to your three rings to draw 96amps, bear in mind that most appliances don’t pull their maximum load. Only things like instant water heaters/ showers do that, and they are never plug in items (maximum 13A On a plug. )
     
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  11. FrodoOne

    FrodoOne

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    An RCD at the CU in series with the MCB supplying any circuit will also protect any "worker" who inadvertently comes in contact with the wires in a cable - such as when driving a nail into a wall. (It will not protect the circuit "wiring" - from overload - but a RCBO will protect any worker, user and the wiring.)
    While it may not be necessary to protect "workers" on "Lighting Only" circuits in this way, unskilled workers have been electrocuted in this country by inadvertently coming into contact with non-RCD protected Lighting circuits. This caused regulations to be changed to require RCD/RCBO Circuit Breakers on all (new/altered) final sub-circuits - including lighting only circuits.
    No doubt it will take a few similar deaths in other countries before the regulations are changed in those countries.

    While the cost of RCBOs on each and every circuit is still somewhat higher than having RCDs protecting several circuits with MCB overload protection, the difference is not very great and there is the convenience of knowing which circuit has activated any RCBO concerned as compared to not knowing which circuit has caused an RCD, which is "protecting" (the user of) a number of MCB protected circuits, to trip.

    https://www.abc.net.au/news/2014-03-17/young-men-who-died-in-insulation-scheme/5322168
    https://memberarea.necawa.asn.au/Ad...eries-regarding-rcds-and-the-new-wiring-rules - Note points 3.c and 3.d (Unfortunately, there is still point 3.e)
     
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  12. TofuSpaceship

    TofuSpaceship

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    sorry for being pedantic, but I really like a fully understaning!
    I am aware that is unrealistic to think to have a load of more than 60A on 3 rings, but if it were to happen, would the RCD blow?
    Or is it as @AndyPRK points out, the main house fuse will probably be only 60A, so that fuse would blow first (is it an actual fuse we are talking about?)
    Sorry for the silly questions!
     
  13. TofuSpaceship

    TofuSpaceship

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    very informative, thank you.
    It is actually on point information, as one of the plasterer got electrocuted meanwhile plastering the ceiling! The lighting CB (without RCD) tripped and he wasn't seriously injured luckily.
     
  14. FrodoOne

    FrodoOne

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    I am sorry to be pedantic and not to mitigate the seriousness of the event BUT, if a "plasterer got electrocuted meanwhile plastering the ceiling" he would be dead, since "electrocution" means "Death caused by electricity".

    From your post, it is probable that he received a non-fatal electric shock.

    If "the lighting MCB (without RCD) tripped and he wasn't seriously injured" it is likely that, at the same time, a "short circuit" was caused which caused the MCB to operate - in overload protection. Had that not happened, the outcome may, unfortunately, have been very different.

    Again, not to mitigate the situation, it is probable that the electric shock occurred only across his fingers and not from one hand to another limb, across his heart - which is a very different situation.

    Can you perhaps see why Australian regulations have now been changed to require RCD/RCBO protection for workers and users on all final sub-circuits .
     
    Last edited: 27 Feb 2020
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  15. TofuSpaceship

    TofuSpaceship

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    Thank you for being pedantic (I am one myself) and thanks for correcting my terminology.
    Just so we are on the same page, I am all about safety and thanks to the inputs of you guys I am understanding it is next on the list to call our own indi leccy to come round and convert all of the CBs to RCBOs or fit a couple more RCDs.
     
  16. FrodoOne

    FrodoOne

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    RCBOs should take up the same space as equivalent MCBs on a DIN CU but additional RCDs will take up more space!
     
  17. EFLImpudence

    EFLImpudence

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    I don't think that was pedantic.

    Meanwhile:

    RCBOs are RCDs. :)
     
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