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Cian79
Hi guys,I'm getting a 0.00 reading at the mains for loop impedance and fairly low readings on the circuits.My r1+r2 is higher that all the loop readings on each circuit.This has never happened to me before.Can someone explain why?
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    Cian79:

    Hi guys,I'm getting a 0.00 reading at the mains for loop impedance and fairly low readings on the circuits.My r1+r2 is higher that all the loop readings on each circuit.This has never happened to me before.Can someone explain why?


    Leads not zeroed?


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    Or battery low?

       - Andy.
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    What sort of meter are you using - a digital reading of 0.00 just means 'less than 0.01', or PSSC of >23kA which is high, but maybe not impossible,  (how close is the substation ?) and look  in the booklet that came with the meter quite often the accuracy is not as good as the precision.  (so 0.01 +/- 3 digits in the last place or something) That is created by subtracting the lead nulling measurement, so equally a good clean and polish of the meter leads and the sockets on the meter that  they plug into, followed by a re-nulling may be in order. Can you borrow another meter and cables to check against?
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    I did that in Hereford a few years ago and asked the customer where the transformer is, about six feet away on the other side of the wall he replied.


    I have had a few low readings in peoples homes, but that’s the only zero I remember.


    Andy Betteridge
  • Former Community Member
    0 Former Community Member
    Zs readings can be affected by parallel earth paths, which may be why the loop readings are lower than the R1+R2.
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    Depends on the make of meter, but I've had issues with Megger 17xx series with loose connections on the input jacks. Using a 3 wire LO current test will give lower readings that 2 wire High current due to intermittent contact.


    not my tester (I'm not the QS on the job, just the guy who knows the connections are dodgy..). Repeated 'calibrations' haven't fixed the fault. It drives me mental
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    Sorry missed this in order to post my rant. But yes. Clean, polish, and test the meter leads and plugs. The modern 'safety' shrouded leads give less chance for visual inspection, corrosion or dust (dust is very likely in your average installation environment) can be a killer for resistance tests, especially when low and high current readings may be compared.
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    Another possible reason was suggested by somebody from Meggar. The supply current is not purely sinusidal but has all sorts of harmonics and non-sinusoidal waves and spikes that might be, or not registered by your instrument but unable to supply an accurate result, although you should get something registered. It was suggested that a minimum of three readings are taken and then the average is calculated..

    Legh
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    MHRestorations:

    Depends on the make of meter, but I've had issues with Megger 17xx series with loose connections on the input jacks. Using a 3 wire LO current test will give lower readings that 2 wire High current due to intermittent contact.


    not my tester (I'm not the QS on the job, just the guy who knows the connections are dodgy..). Repeated 'calibrations' haven't fixed the fault. It drives me mental


    My Megger 17xx would occasionally give 0.00 readings. New leads made no difference but replacing the connector block sorted the problem - he put a good dose of conductive gel on the internal pins for good measure.


    The instrument MI's also say that 2-high will give the most accurate readings, with 2-lo the least.


    F


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