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Final circuit definition BS 7671 / IEC 60364

AL

Hello,

I'm looking for an outside opinion on the "Final circuit" definition.

As per BS 7671, a final circuit is: A circuit connected directly to current-using equipment, or to a socket-outlet or socket-outlets or other
outlet points for the connection of such equipment.

Can the circuit between a distribution cabinet (say 1FC1 MCB) and a control cabinet (1FC1 MCB - 1TA1 AC/DC PSU) be considered a final circuit, or is it just a distribution circuit?

This tends to come up when selecting the appropriate Zs expected for this circuit, on whether it is a final circuit and thus 0.4s disconnection time must be selected, or a distribution circuit and then 5s is the required disconnection time.

Thank you,

Adrian

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  • 0 in reply to AJJewsbury

    Hello Andy, generally between 6 to 20A.

  • 0 in reply to AJJewsbury
    AJJewsbury said:
    Over 32A 5s disconnection time would apply even to a final circuit...

    Unless that circuit also has socket-outlets, although in this case, I guess we wouldn't be debating whether it's a final circuit or not.

  • 0 in reply to gkenyon

    What if it's a wall-mounted socket 32A, 3PH+E, 400VAC (round, industrial type), BUT it's only used to plug in machinery for testing (only plugged/unplugged once or twice a year). In that case, would it still be a final circuit or a distribution circuit? (Unrelated to my initial request)

  • 0 in reply to AL

    It would need an RCD or a convincing risk assessment that shows it is  justified not to consider it as a general purpose socket. How do you control what gets plugged in ?

    Mike.

  • 0 in reply to AL
    AL said:
    What if it's a wall-mounted socket 32A, 3PH+E, 400VAC (round, industrial type), BUT it's only used to plug in machinery for testing (only plugged/unplugged once or twice a year). In that case, would it still be a final circuit or a distribution circuit? (Unrelated to my initial request)

    230/400 V circuits with socket-outlets rated up to and including 63 A require 0.4 s disconnection time in TN systems (Regulation 411.3.1.1).

    mapj1 said:
    It would need an RCD or a convincing risk assessment that shows it is  justified not to consider it as a general purpose socket. How do you control what gets plugged in ?

    In addition to basic disconnection time requirements as above, socket-outlets rated up to and including 32 A require additional protection by 30 mA RCD (Regulation 411.3.3). For the purposes of this provision, the socket-outlet can have the additional protection, rather than the circuit.

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