resistance testing ring main! help!!!!!
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po5hscott
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resistance testing ring main! help!!!!!

Post by po5hscott » Sun May 31, 2009 8:30 pm

i have just tested r1, r2, and rn, the results as follows:-

r1 = 0.46
r2 = 1.24
rn = 0.47

r1 and rn results are similar which they should, but r2 is much higher than it should, i belive should only be 1.67 times that of the phase conductors due to the reduced size of the cpc.....any suggestions why im getting such a high reading....the property is approx 40 years old. i hace niceic inspection shortly and would like to have all the answers or be able to fix the problem..

cheers scott

kbrownie
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Post by kbrownie » Sun May 31, 2009 11:40 pm

Is the CPC, connected to any parallel paths, is metal conduit also forming part of earth path have you disconnected that and pig tails to back boxes.
KB

po5hscott
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Post by po5hscott » Mon Jun 01, 2009 4:33 pm

[quote="kbrownie"]Is the CPC, connected to any parallel paths, is metal conduit also forming part of earth path have you disconnected that and pig tails to back boxes.
KB[/quote]

thanks for the reply, no other parrellel paths to the best of my knowledge, no earth condiut is used, but the cpc'c are connected to metal back boxes.

kbrownie
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Post by kbrownie » Mon Jun 01, 2009 10:15 pm

Try checking all CPC are tight in terminals this could also effect reading and you have good contact with your probes/croc-clips on the in and out CPCs
KB

sparx
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Post by sparx » Wed Jun 03, 2009 7:42 pm

Hi,
as the installation is 40yrs old the chances are the cpc is in fact 1.0mm not 1.5mm as now, this was normal in the 1960's, try a recalc based on that.
Any parallel earths would reduce your reading rather than increase it so don't think thats an issue,

regards & good luck,
SPARX

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