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Panel Isolators - Different Voltages?

Les Spiteri
Where different voltages are fed into a panel is it permitted to isolate them both through the same isolator?
  • For example where you have a Main Fused Isolator for an incoming 3ph supply and a 110Vdc incoming from a UPS?

  • My experience says that as you quite often get auxiliary isolation contacts then it is possible.

  • However should these auxiliary contacts only be used for signalling and therefore cannot be used as a mean of isolation?

  • Also I frequently see 3 or 4 pole isolator used for single phase supply so can you use the remaining contacts to isolate another voltage?


Any thoughts would be most welcome.
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    Les Spiteri:

    Great comments guys, gkenyon could you expand this statement? 

     


    Means of isolation should be able to be secured to prevent accidental re-energization, for safety in testing, maintenance, repair, etc, activities.


    If you use contactors to provide isolation of a supply (whether that supply is LV or ELV doesn't matter ... and I'll expand on this later), you need to be able to either:

     - mechanically secure ("lock off") the contactors in the isolated state

     - secure the switch operating the contactor in the disconnected (open) state, AND ensure that no test equipment that might ever be used during "dead operations" during repair, maintenance and testing, can energize the contactor - for example, accidental voltage or current injection from a piece of test equipment or a test circuit.


    Why not necessarily a difference between ELV and LV? Well, with many ELV supplies the danger is not necessarily electric shock, but fire, arcing, heat and burns ... and potentially arc flash ... for example with supplies that have secondary batteries. Isolation and safe working practices can therefore be equally important with ELV circuits, as with LV, and all of these types of danger are covered by Electricity at Work Regulations.


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  • 0
    Les Spiteri:

    Great comments guys, gkenyon could you expand this statement? 

     


    Means of isolation should be able to be secured to prevent accidental re-energization, for safety in testing, maintenance, repair, etc, activities.


    If you use contactors to provide isolation of a supply (whether that supply is LV or ELV doesn't matter ... and I'll expand on this later), you need to be able to either:

     - mechanically secure ("lock off") the contactors in the isolated state

     - secure the switch operating the contactor in the disconnected (open) state, AND ensure that no test equipment that might ever be used during "dead operations" during repair, maintenance and testing, can energize the contactor - for example, accidental voltage or current injection from a piece of test equipment or a test circuit.


    Why not necessarily a difference between ELV and LV? Well, with many ELV supplies the danger is not necessarily electric shock, but fire, arcing, heat and burns ... and potentially arc flash ... for example with supplies that have secondary batteries. Isolation and safe working practices can therefore be equally important with ELV circuits, as with LV, and all of these types of danger are covered by Electricity at Work Regulations.


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