The protective conductor resistance is usually measured with an appliance tester (Benning, Gossen Metrawatt, or similar).
In addition to regular calibration of the appliance tester, the actual measurement procedure is also very important.
In our experience, there are always measurement errors due to one of the following problems:
Test leads not correctly compensated.
Correctly compensated test leads are essential when measuring the protective conductor resistance.
This means that all test leads, adapters, terminals, etc. used during the measurement must be compensated on the appliance tester before the measurement.
Otherwise a few tenths of an ohm will quickly be added to the actual measurement result.
Please check the compensation procedure in the instructions for your appliance tester.
Cable of the object to be measured not uncoiled.
Many appliance testers measure the protective conductor resistance with an alternating current.
Therefore, a cable of an object to be measured (e.g. cable reel) must always be completely uncoiled.
Otherwise, an inductance is created via the unwound cable, which generates an additional reactance during the measurement and thus falsifies the measurement result.
Incorrect cable length configured.
As a rule, you must set the length of the cable whose conductor resistance you want to measure on the appliance tester. If you have set an incorrect length, the measured value will also be falsified.
If all possible sources of error during the actual measurement are observed and excluded, all measurement results are usually positive.
We therefore ask you to observe the points mentioned above and to repeat your measurement in order to exclude possible sources of error.
Translated with DeepL.com (free version)