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is a discontinuous CPC, where all accessory points are Zs good, on a RFC, with no RCD protection, potentially dangerous or just needing improvement ?

psychicwarrior

as time moves on and opinions shift - especially via pressure from changes in Regs, H&S, CP Scheme influencers;   what was once safe is now not safe and all that !

e.g some now may consider the lack of RCD additional protection to skts  (even if everything else is ok)  is a potentially dangerous situation, where as previously that may not have been the case; same goes for lack of RCD to lighting circuits and even more so if circuit serve/pass a bathroom .

therefore, to the subject question as written ...  what's the consideration 'today'  please ?

and then, same question but where RCD protection on the RFC is present ?

and best wishes to all for a lovely day

Habs

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  • 0

    How can there be a satisfactory Zs when there is no CPC. "Discontinuous CPC" to my mind = no CPC.

    However, if you mean that only one CPC is connected to the MET, I would say FI. (Or C2, which amounts to the same thing.) Somebody needs to inspect the rest of the ring and find the poor connection.

  • 0 in reply to Chris Pearson

    "How can there be a satisfactory Zs " - because there is at each accessory as each is still connected to one leg of the discontinuous CPC  ?

  • 0 in reply to psychicwarrior
    psychicwarrior said:
    "How can there be a satisfactory Zs " - because there is at each accessory as each is still connected to one leg of the discontinuous CPC  ?

    But only if thermal constrains are met.

    There is a 'max Zs' for protection against electric shock, but also a 'max Zs' for protecting the cpc against thermal effects (at least with a fuse, or in the thermal region of a circuit-breaker).

    In practice, with a 32 A BS 88-3 fuse, Za (loop impedance for thermal effects) is greater than Zs (loop impedance for ADS).

    BUT - if a BS EN 60898 mcb is protecting the circuit, a B32 usually requires at least 2.5 sq mm cpc - but 1.5 sq mm might be OK for prospective fault current levels (at the origin) below 3 kA. So a 'complete ring' cpc might be necessary to meet the thermal constraints.

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  • 0 in reply to psychicwarrior
    psychicwarrior said:
    "How can there be a satisfactory Zs " - because there is at each accessory as each is still connected to one leg of the discontinuous CPC  ?

    But only if thermal constrains are met.

    There is a 'max Zs' for protection against electric shock, but also a 'max Zs' for protecting the cpc against thermal effects (at least with a fuse, or in the thermal region of a circuit-breaker).

    In practice, with a 32 A BS 88-3 fuse, Za (loop impedance for thermal effects) is greater than Zs (loop impedance for ADS).

    BUT - if a BS EN 60898 mcb is protecting the circuit, a B32 usually requires at least 2.5 sq mm cpc - but 1.5 sq mm might be OK for prospective fault current levels (at the origin) below 3 kA. So a 'complete ring' cpc might be necessary to meet the thermal constraints.

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