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Evening all.

Is there a regulation or any guidance regarding live zs testing with loads connected....

Eg zs testing on a 3phase motor whilst it is running. Could the current being drawn damage the meter if testing at the end of line.... Or doing a live zdb test, is there any guidance to say there must be no live loads or a maximum current being drawn at time of test ?

I hope this makes sense I am new to testing and don't want to damage my mft1730 Megger.

Thanks
 

pc1966

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The running motor won't damage your MFT but it can lead to a higher than expected PSCC as the motor has inertial and on slowing works as a generator. As a result it is not really giving you the circuit's Zs value for fault clearing at the supply, since you have in effect a 2nd power source nearby.

In some larger systems where you are trying to work out max fault currents (either for checking MCCB/fuse/switch limits, or arc-flash safety calculations) then the contributions of nearby motors can be significant, at least for a few cycles of the AC as its magnetic field collapses (or it stops, probably later).
 
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