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Howdi all

Started on a new installation last week, changed all skts,light fittings.re wired ktchen and cooker circuit basically replaced almost everything!! today i changed the d/b all circuits with rcbos.all of my testing was spot on until i tested the Zs of each circuit!! My Ze was 0.13 and my R1 N R2 Values all looked good!!!However when a came to test for the Zs my results were all over the place 86.3 68.4 123 ohms!!!!!!!!!!!the multi meggar has just came back from callibration and i have had no problems in the past with this instument.Can this cause damage???? as my readings said that electrical noise was the cause!!! WHAT IS ELECTRICAL NOISE AND HOW DO I FIX THIS??? no data or low voltage cables in the house!!!!

many thanks



might sound like a stupid answer but did you reconnect the main earth after testing Ze
probably no help at all
and sorry i don't know what electrical noise is
some of the multi testers give erratic readings on the no trip scale its best to take more notice of the r1r2 this is more accurate
the noise symbol is like a sinewave with a spike top and bottom on my meter i dont see it often hpoe someone can explain noise to us both


from my understanding of Electrical noise it means you possibly have an induced voltage or current in the Earth. Clamp the earth and have a check. last time i found it it turned out to be the sub mains transformer breaqking dowm and there was 9A going into the installation on the earth.


The megger is notorius for getting upset by "field noise", it's usually displayed by an arrowhead symbol on the display of the meter.

It's usually caused by an induced EMF in the cpc of the affected circuit caused by another circuits chracteristics.

Best thing to do is disconnect ALL cpc's bar the circuit under test from the DB and try again.

Leekemp has also brought up a quite possible reason, an easy mistake to make.
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Thanks all ,tried a diff tester today and all was fine!!!! A think my tester has been NO SWEARING up when it has been callibrated!!!! Still electrical noise not a common thing and after speaking to quite a few sparks not something many of us know about!!1

thanks for the help tho!!
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