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543.6.1 the protective conductor shall be incorporated in the same wiring system as live conductors (re: overcurrent protection)

psychicwarrior

Hello good day to all

In an *all* PVC trunk/conduit wiring system (using insulated single conductors), what is the implication of 543.6.1 ?

- does it mean that a protective conductor (shared or per circuit) has to be in *each* part of the wiring system that a live conductor runs or close by ?

e.g. one cannot send feed and switched live on their own down to a switch with a cpc coming to the switch from elsewhere

If yes or no, what is the safety issue intended to be addressed with this one ?

It feels like I am misinterpreting this.

Cheers

Habs

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  • 0

    Well a Wiring System is defined as "An assembly made up of cable or bus bars and parts which secure and, if necessary, enclose the cable and bus bars."

    543.6.1 is concerned only with "overcurrent protective devices used for fault protection."

    Z.

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  • 0

    Well a Wiring System is defined as "An assembly made up of cable or bus bars and parts which secure and, if necessary, enclose the cable and bus bars."

    543.6.1 is concerned only with "overcurrent protective devices used for fault protection."

    Z.

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  • 0 in reply to Zoomup
    Offline 
    hertzal123 said:
    Thought this was allowed under 543.1.2  if the borrowed cpc was of adequate size?

    But not permitted in general under Regulation 542.6.1 unless ADS is provided by RCD alone:

    542.6.1 Where overcurrent protective devices are used for fault protection, the protective conductor shall be incorporated in the same wiring system as the live conductors or in their immediate proximity.

    So if you really do "pinch the cpc from another circuit", it does not comply in many TN systems.

    Chris Pearson said:
    If you have wired in singles in galvanised conduit, and used the conduit as cpc, it is shared by all the circuits.

    And is the "same wiring system", so there is no problem ... no code required in that case ... but this doesn't apply to pinching the cpc from another circuit wired in T&E etc.

    OlympusMons said:
    Also you are allowed to share CPCs in 543.7.2.201(c) between two identical circuits having high protective conductor currents


    But in that case, each circuit would have a cpc of its own (to comply with Regulation 542.6.1), along with a "reinforcing cpc" from another circuit to meet the additional requirements of Regulation Group 543.7 ?



    At the end of the day, though, a cautionary note for those who think the guidance quoted in the OP is poor advice. What if someone doesn't realise the cpc is taken from another circuit. The circuit from which the cpc is taken is isolated for maintenance, leaving some of the installation intact, and a fault occurs, and someone disconnects the cpc to work on it ... I have only at this point to quote CDM Regulations and Designer's Duties to bring the whole discussion back on an even keel ... only "pinch a cpc" if it's well documented and signposted.

  • 0 in reply to Zoomup

    it is sometimes difficult for me to understand the point(s) you are trying to make 'Z'.  543.6.1 relates wiring system, protective conductor, live conductor and protective device and is not just an 'only', as you seem to imply.

    I have seen other posts on 543.6.1 (and other related regs.).  My (2nd) question  still stands unanswered by you if you were intending to answer any of the three. :-)   If it is poorly worded let me know.   For example, you could just answer yes or no to it for now .

    regards

    (edit: made a small phrasing edit)

  • 0 in reply to psychicwarrior

    "it is sometimes difficult for me to understand the point(s) you are trying to make 'Z'.  543.6.1 relates wiring system, protective conductor, live conductor and protective device and is not just an 'only', as you seem to imply."

    If an R.C.D. is used the problem seems to go away. The use of a protective device that relies upon large fault currents to operate the protective device, such as a fuse or circuit breaker is the issue here with earth faults. As the R.C.D. will operate quicker than a fuse of circuit breaker in most cases of earth fault the cables do less work under fault conditions. There is less chance of a high earth fault current lingering while the protective device considers operating.

    You would run a C.P.C. to all points anyway, such as to switches or socket outlets etc.

    Z.

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