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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
    AL said:
    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?

    That depends on the circumstances.

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

    No-one can provide a definitive interpretation, except a court of law.

    To give an opinion, some more details are necessary as to the arrangement and circumstances.

    For example, what does the control panel do? The circuits from the control panel, in some instances, could be considered 'auxiliary circuits' and these wouldn't strictly be 'final circuits'; in other circumstances today, the control panel is a data communication device only, so is likely to be potentially considered current-using equipment.

    On the other hand, is it part of 'machinery' as defined in the Supply of Machinery (Safety) Regulations?

    The expert providing the opinion might also wish to know what standard(s) the control panel is manufactured or assembled to.

  • 0 in reply to gkenyon

    Thank you for the reply.

    The control panel contains an AC/DC PSU and a PLC rack.

    To this PLC rack, we have several field devices connected, such as Safety Interlock Gates, Pushbuttons, Signaling Beacons and Sensors, all 24 VDC supplied. 

    The AC supply branch doesn't extend beyond that one PSU.

  • 0 in reply to AL

    You could look at this both ways.

    The PSU converts electrical energy to electrical energy ... so is not, by definition 'current-using equipment'.

    Some of the 'field devices' do, however, do so ... so the control panel definitely supplies final circuits.

    You did not provide which standards the control panel is manufactured or assembled to, but it could be classed as a 'switchgear or controlgear assembly' (BS EN 61439 series, or its predecessor BS EN 60439 series), or 'electrical equipment of machines' (BS EN 60204-1)

    One could take the view, if the former standards (EN 61439 / EN 60439), the AC supply to it is more likely to be considered a distribution circuit, whereas the latter standard, the 'machinery' as a whole could well be 'current-using equipment', and therefore this, being part of 'machinery' could make the AC supply to it a final circuit.

  • 0 in reply to AL

    On the other hand, you could decide the PLC converts some electrical energy into heat ... so it's current-using under all circumstances. However, pedantically, is the circuit that supplies that inside the panel protected by an Overcurrent Protective Device in the Panel? If so, that is the final circuit, and the supply to the panel is a distribution circuit.

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  • 0 in reply to AL

    On the other hand, you could decide the PLC converts some electrical energy into heat ... so it's current-using under all circumstances. However, pedantically, is the circuit that supplies that inside the panel protected by an Overcurrent Protective Device in the Panel? If so, that is the final circuit, and the supply to the panel is a distribution circuit.

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  • 0 in reply to gkenyon
    gkenyon said:
    On the other hand, you could decide the PLC converts some electrical energy into heat ... so it's current-using under all circumstances.

    Just like any cable or switchgear, etc.

    Is a relay current-using equipment?

    I think that the purpose of the equipment is important. "electrical equipment intended to convert electric energy into another form of energy" (my emphasis).

    I am less clear on control gear which has some form of display, given that the light which is emitted is intended rather than being merely incidental.

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