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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,

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    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. 

    If it is as most of us suspect a broken c.p.c. with capacitive coupling to other conductors providing the voltage, then be aware that the values displayed on the voltmeter can be extremely variable. One meter might show 55V another 15V and another 115V - all quite validly. The problem is that the capacitance is normally of very low values - pico Farads - so the current that can flow is tiny, thus the internal impedance of the voltmeter can significantly alter the circuit being measured. Even the best voltmeters draw a little current from the circuit and if there is only a tiny current available the voltage will reduce even before the meter gets a chance to measure it - it's all down to the details of innards of the voltmeter - which can vary considerably.

       - Andy. 

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  • 0

    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. 

    If it is as most of us suspect a broken c.p.c. with capacitive coupling to other conductors providing the voltage, then be aware that the values displayed on the voltmeter can be extremely variable. One meter might show 55V another 15V and another 115V - all quite validly. The problem is that the capacitance is normally of very low values - pico Farads - so the current that can flow is tiny, thus the internal impedance of the voltmeter can significantly alter the circuit being measured. Even the best voltmeters draw a little current from the circuit and if there is only a tiny current available the voltage will reduce even before the meter gets a chance to measure it - it's all down to the details of innards of the voltmeter - which can vary considerably.

       - Andy. 

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