how do i test for earth ?


Postby andy-10 » Mon Nov 05, 2007 2:28 pm

hi,

I've just moved into a new flat and want to test that all of the water and central heating pipes have been earthed properly.

Can I use a multimeter to do this ? How exactly do I do that ?

(I have access to the main earthing lead in the fuse box.)
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Postby sparks » Mon Nov 05, 2007 8:59 pm

multi meters are not usually used for testing earths a low resistant ohm or continuity meter is used for this ,some multi meters are not accurate enough for this purpose, so how do you check ,regulations state that bonding to any service should be made within 600mm of the incoming service water gas etc. bonding should be made to basins and baths pipe work and radiators in bathrooms.the main bonding to water should be a minimum of 10mm with any supplimentry bonding 6mm . to test the earths ,ensure the supply has been isolated and disconnect the earth ,connect an earth to the earth bar at the mains board then test between that cable and the point of connection to the incomming service ,this method is know as the long lead method ,once test carried out dont forget to reconnect the earth
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Postby kuzz » Mon Nov 05, 2007 9:16 pm

Your most important bonds (Equipotential) should be between the earth bar in your consumer unit & your water stop tap & gas meter. You can check this for continuity by disconnecting both ends then use your multi meter on a low ohms scale with a long lead. Your supplementary bonding you should be able to see (the connection between hot & cold pipes)
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Postby sparx » Mon Nov 05, 2007 10:03 pm

Hi Andy, you could use a multimeter on Ohms low scale with a long wander lead from main earth connection to one lead and use the other one as test prod, BUT you may well get misleading results due to the very low amount of power from such a meter.
The meter used for such tests to comply with wiring regs has to generate a high current to simulate fault conditions, this will overcome joint resistances ect, so really its not a DIY job with basic multimeter,
regards SPARX
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Postby andy-10 » Wed Nov 07, 2007 2:44 pm

thanks for all your help; much appreciated.

andy
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