Conduit as earth????

[mickytuff]

Hi all done some testing work at a hospital and the orignal wiring was done in metal conduit, now the zs figures tested all good, my question is can u calculate the r1 and r2 figure when their isnt an earth cable as such???

 

[MarkieSparkie]

Ok nickblake here we go...............while testing with a megger multi, if you chose to test on notrip on your loop test, why do U have to connect all three leads, if you connect just line and earth it wont produce a reading and just say trp on the display, yet when you deselect no trip it tests fine with just two leads connected, so there you go, any body else had same problem???????????

In "No-trip" mode the Megger MFT electronics requires 3 wire L, N and E connections for power and reference so that the sophisticated method of noise cancellation that the Megger uses can resolve the impedance from the low level "No-trip" current pulses, even in an electrically noisy environment. It is because of this multiple current pulse and noise cancellation technique that the Megger gets unfair criticism from users of other MFTs (Fluke particularly) for it's apparently slow "No-trip" test, however, Megger users get the last laugh because they very rarely have their test inhibited by a noise error.