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Possibly changing the 5 Second Disconnection Limit

Former Community Member
Former Community Member
I'm doing some theoretical calculations, and I'm debating that the 5 second disconnection may have to be lowered in circuits 32-225 amps where fed from an extensive LV supply network. IMO, The voltage may not sag far enough at the supply terminals to result in a touch voltage of 50-75 volts to remote earth. On the other hand, large circuits may be relaxed to 10 seconds and 15 seconds with no ill effect from a basis of shock protection.


I'm also debating that adiabatic limits make an assumption of 10 seconds disconnection for circuits 63 amps and below on the basis of external Ze changes.


Granted these changes would be on orders of magnitude more prudent for NFPA-70 and CSA C22, however it is still worth considering.


Right now I am putting together a frame work for various touch voltages for given network configurations and interior wiring practices seen around the world.  

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  • Former Community Member
    0 Former Community Member
    mapj1:

    Ah well at some point in your lists do cover the UKs unique 110v folly of the 55-0-55 Reduced Low Voltage (RLV) service for building sites.  (sometimes actually 2 phases at 66 volts and 120 degrees apart, but the 110V drill does not care so much)

    When you do the sums on that neither RCDs nor fuses seem to be that important.


    Note that 5 seconds is as good as forever in terms of electrocution - the big change in the graph is around half the period of a human heartbeat, for very good reasons when we think about how the muscles do their thing.

    As far as I know in the UK, at least for the last 50 years or so,  the intention was never that someone would be holding an item with a 5 second disconnection time, as that was not really intended for final circuits supplying earthed portable equipment.

    Mike.




    There is also the 133/230Y system, which I personally like.


    I've come to that conclusion as well. It appears 5 seconds is not meant to take a user holding on to an item while exposed to remote earth. And there may be a practical reason for the assumption as I'm crunching the numbers. 


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  • Former Community Member
    0 Former Community Member
    mapj1:

    Ah well at some point in your lists do cover the UKs unique 110v folly of the 55-0-55 Reduced Low Voltage (RLV) service for building sites.  (sometimes actually 2 phases at 66 volts and 120 degrees apart, but the 110V drill does not care so much)

    When you do the sums on that neither RCDs nor fuses seem to be that important.


    Note that 5 seconds is as good as forever in terms of electrocution - the big change in the graph is around half the period of a human heartbeat, for very good reasons when we think about how the muscles do their thing.

    As far as I know in the UK, at least for the last 50 years or so,  the intention was never that someone would be holding an item with a 5 second disconnection time, as that was not really intended for final circuits supplying earthed portable equipment.

    Mike.




    There is also the 133/230Y system, which I personally like.


    I've come to that conclusion as well. It appears 5 seconds is not meant to take a user holding on to an item while exposed to remote earth. And there may be a practical reason for the assumption as I'm crunching the numbers. 


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