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Live - Neutral reverse from plug in tester

Former Community Member
Former Community Member

Hi, being retired for 2 years i was in trade as domestic electrcian for 10 years then commercail for next 40 years. So have high level od experience in field, yet never experienced the below unrational fault.

Really baffling me now (and an  independant competant electrican contractor) is a recent problem where i found using Martindale plug in tester (also using  independant contractors KEW plug in tester) that on a ring circuit somewhare in its middle 2 outlets read L-N reverse.

Yet taking off the outlets, the cables are connected correctly and live tested live in its correct position so Plug top fuse was correctly protecting appliances. This is on a recently extended ring circuit for room extension. I have read other blogs where they say the earth could be live or at least have a voltage presence, or that the earth CPC in fact could be floating so having volts induced to it.  Both scary thoughts.   

Any one had same issue please and what was found to then correct fault. 

I have yet to do a local earth test of the cpc at the two outlets and check the consumer unit earth connection to the main incoming supply.  Also all other outlets in house test correctly so assume main earth connection is not a problem and the RCD as main isolator passes its tests,

  • 0

    Good, so N to local earth (plumbing rads etc )is 0v, and just the circuit CPC is flapping about at about quarter of the way up the L-N voltage. My money is on an open CPC, and a voltage divider formed by the capacitive coupling from L-CPC and N-CPC.

    In the middle of a ring this means 2 breaks in the CPC, one on either side, or something really silly, like the back box is earthed but not the socket.

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    So, for some reason the C.P.C. at the sockets is 55 Volts above N. The earth is deficient in some way. That accounts for the 185 Volts from L to E rather than the expected 240 Volts. Curiouser and curiouser.

    Z.

  • Former Community Member
    0 Former Community Member

    L-N 240 vlts. L-E 185 vlts; N-E 55 vlts, indictaes i think that somehow L is leaking across to E somewhere local, i think a plastered in joints are suspect. Its odd why RCD dont trip but maybe reduced voltage in middle of circuit is not enough milli amos leakage to trip 30ma RCD at board.

    Have not had chance yet to perform proper tesing with insulation and R1-R2 tests. At least no local metal work like rads are reading this 55vlts to a N   point. and all oultes have 240 L-N voltage so no under volts present for appliances. I know telephone line operate arounf 50 volts and IEE regs recognise that 50 volts or under are not considred danger to life. But this circuit is not at an acceptable condition to be left at fault. still waiting for opputunity to test correctly. 

  • Former Community Member
    0 Former Community Member

    Mikesparky: 
     

    hi thank you all for replies, there all as i guessed, so when allowed will do all thats recomenend by you Taking ring out of consumer unit to do full circuit tests of insulation then R1 -R2 tests and then use  a tone generator to see if any fixings local to faulty outlets pick up the tone in case a fixing has pierced cable but not enough for RCD to trip, unlikely but feasably possible. 

    Its going to be a long job. my findings i wil publish here but may not be for a few weeeks. Having left the two dodgy outlets unuseable to occupier.

     

  • Former Community Member
    0 Former Community Member

    hi thank you all for replies, there all as i guessed, so when allowed will do all thats recomenend by you Taking ring out of consumer unit to do full circuit tests of insulation then R1 -R2 tests and then use  a tone generator to see if any fixings local to faulty outlets pick up the tone in case a fixing has pierced cable but not enough for RCD to trip, unlikely but feasably possible. 

    Its going to be a long job. my findings i wil publish here but may not be for a few weeeks. Having left the two dodgy outlets unuseable to occupier.

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    A bedtime story,

    Once upon a time…

    IET Forums - Reverse Polarity At All Sockets (theiet.org)

     

    Z.

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    Yet taking off the outlets, the cables are connected correctly and live tested live in its correct position 

    The problem must be with the N or E then.

     

    Z.

  • 0
    • The CPC could be live.
    • There could be two breaks in the neutral with an appliance plugged in between the breaks.
    • The live and neutral could be be reversed.
  • 0

    If the tester plugs have an illuminated indicator showing L-N reversal it must be because the light connected between N and E is being supplied by a Voltage difference between  N and E with regard to the opposite terminal pin of the tester plug. So either E has a raised potential, or N has a raised potential. There is a potential difference between both. Why? Needs further investigation.

     

    Z.

  • 0

    Those testers are no substitute for the traditional ring tests and IR.

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