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Electric Shock from Old P.I.R. Floodlight.

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Today I was asked to investigate why an old outside P.I.R. tungsten halogen floodlight did not work. It had been installed on a 70s holiday chalet. The owner had installed it himself and admitted that he did not know much about electrics. I used my aluminium ladder to access it, the ladder has plastic feet and it stood on a concrete surface. When I went up to the floodlight my Voltstick suggested that the supply cable was dead. But when I touched the fitting I got a shock, this before I had removed the terminal box  cover. Anyway, after turning off at the consumer unit I noticed that the owner had fitted the live supply wire into the earth terminal. That was the cause of the shock I imagined. Anyway I removed the old floodlight and was going to fit a new L.E.D. one. I tested at the supply cable but there was no supply. All M.C.B.s were on and the R.C.D. was on as well. So how did I get a shock if the supply cable was dead? A charged capacitor perhaps? Or induced Voltage? No switch was found that controlled this cable.


I got a reading of about 2 Volts from the main P.M.E. earth terminal and a temporary earth rod bashed into the lawn.


There are three 11kV overheads about 30 metres away from this chalet.


Any ideas please?


Z.
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    Was it only dead after you touched it and something has since tripped/blown. Or, is your ladder live in that position?. A live wall is not totally impossible if there has been a cable nailing accident , and the wall is damp. Clearly in some odd way this cable is not completely continuous. I'd half expect supply  to come off the back of the nearest light switch, and only to work when the hall light is also on (or only if it is off if they use the back contact of a 2 way switch.)
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    Was the owner able to tell you when the outside PIR lamp failed or had it not been working for several years?


    Legh
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    mapj1:

    Was it only dead after you touched it and something has since tripped/blown. Or, is your ladder live in that position?. A live wall is not totally impossible if there has been a cable nailing accident , and the wall is damp. Clearly in some odd way this cable is not completely continuous. I'd half expect supply  to come off the back of the nearest light switch, and only to work when the hall light is also on (or only if it is off if they use the back contact of a 2 way switch.)




    Ladder insulated from ground and wall by plastic feet at both ends.


    Wall dry.


    Cable appeared dead initially using Voltstick. Cable never found live using Voltstick, Voltage tester and finally digital multi meter.


    Z.

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    Legh Richardson:

    Was the owner able to tell you when the outside PIR lamp failed or had it not been working for several years?


    Legh




    The old floodlight was inherited from a relative. But it would not have worked in its new location as it had live connected to earth in its terminal box.


    Z.

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    Zoomup:




    Legh Richardson:

    Was the owner able to tell you when the outside PIR lamp failed or had it not been working for several years?


    Legh




    The old floodlight was inherited from a relative. But it would not have worked in its new location as it had live connected to earth in its terminal box.



    But what if the N cable was connected to L? I assume no RCD in the circuit.


    Any road, thank God that the shock didn't tip you off the ladder.

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    Zoomup:




    Legh Richardson:

    Was the owner able to tell you when the outside PIR lamp failed or had it not been working for several years?


    Legh




    The old floodlight was inherited from a relative. But it would not have worked in its new location as it had live connected to earth in its terminal box.


    Z.


     




    It would work with the neutral conductor in the live terminal and the live conductor in the earth terminal, presuming that there is not an RCD on the circuit.


    Andy Betteridge 

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    So if you were to make the correct connections to the PIR lamp, even though there appears to be no supply, would the light come on one wonders?


    Wellies and marigolds would be advisable ...


    Legh
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    I think you got a shock because of voltage on the earth lead you said you saw around 2 volts between the PME Earth and a lawn earth well what's to say that when you went up the ladder there wasn't  more on it if for instance the owner was cooking something or the immersion heater was on causing more voltage on the CNE wire




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    As to the initial 'dead' from the volt stick.. remember they use the user as an earth reference (by capacitance only of course). So the 'live wall' (which is definitely plausible if the LIVE bodied floodlight was bolted to it) would cause it not to react. The more puzzling bit is how you got the shock. Maybe you got unlucky and the 'insulation' between the ladder and true earth potential broke down as you shifted your weight to touch the light?


    The more I see around, the more I see why they tried to eliminate DIY electrics...
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    It would work with the neutral conductor in the live terminal and the live conductor in the earth terminal, presuming that there is not an RCD on the circuit.



    In which case the floodlight would have supply N and PE connected across its L & N terminals - so we'd need something else very strange to be happening with the supply cable (like L-N reversal) to get a filament to light.


      - Andy.

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