Zdb dodgy reading

[nicsin02]

Hi guys, I'm at a job the now testing a d/b when testing a Zdb on a 3-phase board br- <0.01 bl- 0.09 gr- 0.09, what would cause such a difference in result, it comes from the meter to a busbar and then to the d/b, all 3 cables same size and same length of run, I will try to see if its slack connection when the power goes off but I doubt that will be the answer? Any thoughts guys cheers

 

[Richard Burns]

You are near the resolution limit on your meter so a tiny change could cause this. Connection to the meter, make sure you are not on an oxidised section with your probes, or as you say it maybe just a slightly looser termination, but less likely.

 

[Engineer54]

Hi guys, I'm at a job the now testing a d/b when testing a Zdb on a 3-phase board br- <0.01 bl- 0.09 gr- 0.09, what would cause such a difference in result, it comes from the meter to a busbar and then to the d/b, all 3 cables same size and same length of run, I will try to see if its slack connection when the power goes off but I doubt that will be the answer? Any thoughts guys cheers

Not that i can see anything wrong with your tested values, but at those sort of values your probably not getting accurate values anyway, as your MFT or whatever, hasn't got the resolution to accurately measure values down to 0.01!!

Generally any differences in values will be normally down to the connections torque values, at these sort of low Zdb values.......

Check out this Sticky by IQ ....http://www.electriciansforums.net/i...38-higher-accuracy-low-ze-test-procedure.html