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Isolating multiple supplies

Udtwmc
I have two supplies of different types coming into a distribution rack

(type 1 : 230V 1Ph+N  max load 25A

type 2 : 110VAC reduced low voltage / centre tapped earth max load 55A ) 


id like if I can to isolate both using one 63A 4 pole isolator (coloured red yellow for emergency switching off). I can see from both the wiring regs and EN 60204 (this machine will require CE Marking) that every supply requires a means of isolation, but I can’t be sure if this means it’s own independent isolator. I kinda feel that I shouldn’t be mixing different supply types on the same isolator but then it would be actually useful in this particular installation. So is this bad practice?


  • 0
    Unfortunately I think it is quite clear in BS EN 60204 Sect 5.3.1:

    "A supply disconnecting device shall be provided for each incoming source of supply to a machine".


    I sympathise though, as a 4 pole isolator would provide sufficient isolation between the supplies and if clearly labelled would not, in my opinion, compromise safety, however it would be classed as a single supply disconnecting device, thus, for one supply only. 


    Now if you look at the Craig & Derricott SD00406B you will see a common handle with 2 physically separate isolator blocks, each block is a separate disconnecting device so that should meet the requirements of 60204.  This particular device doesn't meet your switching requirements, only 40A, but a bit of research may uncover one that does.
  • 0
    Now I've re read the statement from 60204, I think it is quite clear!


    Thank you for the link to the 2-block isolator, i had no idea there was such a thing on the market although I'd still class it as a single isolator. Guess I'll stick 2 isolators on the DB rack.


    Cheers
  • 0
    It is quite common, and often very desirable  to gang switches so that supplies are obliged to be isolated together, rather than separately.  This is no sillier than switching all 3 phases together when the downstream load is 3 fuseboards of single phase equipment, or the isolation of off peak and 24hr mains from a common point in a building with storage heaters.  (where it could be one of these. )

    In your cases the voltages are different, but so long as the inter stage insulation exceeds the highest present there is no technical objection.

    It is always possible that an international standard failed to foresee a common situation however.

    Another approach would be shunt trips on a common stop, so one out all out.



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