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Reverse Polarity

bakey1959

Has anyone encountered a reverse polarity single phase PME supply to a house? If so, how did it happen and how was it detected?

I am intrigued to how you would discover it by measuring L-N, L-E, and N-E at the incoming side of the Main Switch, as the Earthing conductor would be connected to the Line at the cut-out and give 0V, the same as if it were correctly wired and you were measuring N-E?

I cannot get my head around how you would detect the issue.... maybe I will set it up on an empty standalone C/U and see what I get?

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  • 0

    It could get reversed in several ways, common occurance is when the meter is changed

    At the main cut out

    At the meter

    At the CU/DB

    At the socket

    Ways to check

    At the main cut out L should be on the fuse carrier side can confirm with a Contact stick and/or GS38 to E and/or lamp meter L to E.  N will not light lamp or sound contact stick

    At the meter N should be the 2 middle cables can confirm with a Contact stick and/or GS38 to E and/or lamp meter L to E.  N will not light lamp or sound contact stick

    At the CU/DB Contact stick and/or GS38 to E and/or lamp meter L to E.  N will not light lamp or sound contact stick

    At the socket use a 3 pole plug in tester or use MFT to test polarity

    If there are connector blocks in the mix they are also a source where polarity can be reversed. 

  • 0 in reply to Sergio Fernandez

    At the main cut out L should be on the fuse carrier side can confirm with a Contact stick and/or GS38 to E and/or lamp meter L to E.  N will not light lamp or sound contact stick

    LAmp/ meter will not work on a PME supply if the 'E' you use is (due to reversal) the live one.  In a well isolated location - like an upstairs maisonette fed by plastic water pipes or something, you could have the whole installation CPC alive and not feel very much, and the tester may show good when it isn't

    The non contact probe may or may not work as well as you expect, depending on how much of an equipotential zone the building made - don't forget that the second terminal of the volt-stick is the capacitance to the local environment, augmented by that of the user.

    I have heard of both L and N/E showing as live for a non-contact tester, but not seen it myself.

    Mike

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  • 0 in reply to Sergio Fernandez

    At the main cut out L should be on the fuse carrier side can confirm with a Contact stick and/or GS38 to E and/or lamp meter L to E.  N will not light lamp or sound contact stick

    LAmp/ meter will not work on a PME supply if the 'E' you use is (due to reversal) the live one.  In a well isolated location - like an upstairs maisonette fed by plastic water pipes or something, you could have the whole installation CPC alive and not feel very much, and the tester may show good when it isn't

    The non contact probe may or may not work as well as you expect, depending on how much of an equipotential zone the building made - don't forget that the second terminal of the volt-stick is the capacitance to the local environment, augmented by that of the user.

    I have heard of both L and N/E showing as live for a non-contact tester, but not seen it myself.

    Mike

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