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Double pole switches for lighting

Kenneth Odam

I replaced an old fluorescent light fitting with an LED version - it had an emergency backup facility which required a separate unswitched live.

I took a live feed from an existing emergency light to my new fitting.

Everything seemed to work until I turned off the light - the battery charging light went off and the light came on at low power.

It turned out that the original light circuit had a double pole switch.  When it broke the neutral line the emergency light came on.

I bypassed the neutral side of the switch and the lights all work as expected.

I have never come across double pole switches used for lights.  Is there any good reason for this?

There is a double pole cct breaker upstream for maintenance work, so I don't think I'm creating a hazard.

In the unlikely event that the live side of the double pole switch breaks in the on position, the neutral switch would turn out the light but leave it all floating at live potential.  I can therefore think of good reasons not to use a double pole switch.

Thanks

Ken 

Retired MIET

Parents

  • It is not common to use a double pole switch for lighting. Reasons to do so include.

    The supply once had BOTH poles live, for example between phases of a 3 phase,4 wire system at 127/220 volts, or between outers of a three wire 120/240 volt system.

    The polarity of the supply is unknown or liable to vary. Esp on mobile or transportable buildings etc. Or provision for a portable generator.

    The neutral was looped via the switch position and someone believed that a double pole switch switch was required.

    A history of switch failures, perhaps due to high wattage fluorescent or discharge lamps, alleviated by fitting a double pole switch.

Reply

  • It is not common to use a double pole switch for lighting. Reasons to do so include.

    The supply once had BOTH poles live, for example between phases of a 3 phase,4 wire system at 127/220 volts, or between outers of a three wire 120/240 volt system.

    The polarity of the supply is unknown or liable to vary. Esp on mobile or transportable buildings etc. Or provision for a portable generator.

    The neutral was looped via the switch position and someone believed that a double pole switch switch was required.

    A history of switch failures, perhaps due to high wattage fluorescent or discharge lamps, alleviated by fitting a double pole switch.

Children
  • in reply to broadgage

    Thanks for the suggestions.

    In this case we have a single phase supply to a permanent building built in the early 1980's.  Each switch ran 4 8ft fluorescent tubes - about 400 watts per switch.  As far as I know nothing has been changed since the building was built

    The neutral and live all go through the same switch panel, Your comment "someone believed that a double pole switch switch was required" therefore looks likely.  Local folklore suggests that it was built by the apprentices.

    I'm tempted to bypass the neutral sides of the switches so that they are effectively single pole.  This would remove the possibility of the live switch failing ON, the neutral being switched OFF and the fitting floating at live.  Can anyone think of a reason why I shouldn't do this?

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