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Unusual voltage measurements

vantech

Hi, 

Just moved into a new build and have 2 questions which have me scratching my head. 

The electrician has used through crimps (so he says on the phone), to join a 25mm armoured and meter tails in a metal junction box. He stated this was inside of the meter cupboard on the outside wall, but it isn‘t. I think this is OK as a setup, however the builder has whacked the joint into the cavity of the wall behind the built in meter cupboard so it isn’t accessible - this of course isn’t acceptable. 

The second finding is that, if the main switch in the DB is turned off, I can measure 230V between L&N and L&E (as expected, PME system) on the input side of the isolator. 

What i am unsure of, is that a measurement between the live side of the isolator and the Neutral (output side of the isolator), shows a voltage of 230V. This neutral output, should be isolated by the main switch. My thought is that perhaps voltage is flowing back to earth through electronic devices that naturally leak to earth?  

The isolator is absolutely working as it should, so no issues there. The voltage must be running back somewhere else . 

I haven’t seen this before, so before I call the original installer i wanted to raise it here first. 

Thanks. 

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    broadgage: 
     

    Subject to the usual caveats regarding proper workmanship and materials, there is nothing INHERENTLY wrong with use of crimp connectors on larger conductors.

    I would perhaps have concerns as to whether the SWA is correctly terminated and as to the correct earthing of the armouring.  Also have the meter tails been extended to a length greater than permitted.

    As regards the voltage readings, I do not find the description entirely clear. Are we talking about a main switch built into a consumer unit, AND a separate isolater.

    If a double pole switch is turned of, there should be no significant voltage between any conductors down stream of  that switch.

    The tails/armoured is at least 6-8 metres long, protected only by the DNOs fuse. This is wrong, I know, but a 100A fuse in a separate isolator is offering the same protection as the DNOs fuse, also rated at 100A. 

    Regarding the measurement. Imagine a DB. You have the incoming supply on top of a main switch, and the outgoing on the bottom. 

    Board is turned off, voltage between L&N and L&E on the input side is 230V and the output side 0V (as expected). 

    If I measure from the live of the input and the neutral of the output, I get 230V. This is what is throwing me. There is a potential between the L input and what should be an isolated N output. The only logical explanation I can think of is N-E leakage on out going circuits, however all are protected by RCBOs that do not nusience trip.  

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  • 0

    broadgage: 
     

    Subject to the usual caveats regarding proper workmanship and materials, there is nothing INHERENTLY wrong with use of crimp connectors on larger conductors.

    I would perhaps have concerns as to whether the SWA is correctly terminated and as to the correct earthing of the armouring.  Also have the meter tails been extended to a length greater than permitted.

    As regards the voltage readings, I do not find the description entirely clear. Are we talking about a main switch built into a consumer unit, AND a separate isolater.

    If a double pole switch is turned of, there should be no significant voltage between any conductors down stream of  that switch.

    The tails/armoured is at least 6-8 metres long, protected only by the DNOs fuse. This is wrong, I know, but a 100A fuse in a separate isolator is offering the same protection as the DNOs fuse, also rated at 100A. 

    Regarding the measurement. Imagine a DB. You have the incoming supply on top of a main switch, and the outgoing on the bottom. 

    Board is turned off, voltage between L&N and L&E on the input side is 230V and the output side 0V (as expected). 

    If I measure from the live of the input and the neutral of the output, I get 230V. This is what is throwing me. There is a potential between the L input and what should be an isolated N output. The only logical explanation I can think of is N-E leakage on out going circuits, however all are protected by RCBOs that do not nusience trip.  

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