The best I've seen and heard so far notably on the How the low voltage setting differs from the high voltage setting for fault detection  and its effect on the needle sweep  This truly makes the Megger unique

reviving a very old vid!  thanks for the info.  I was just given an old crank megger and wanted to see how they work.

The low voltage used by a standard multimeter in the "resistance" mode may not detect certain insulation breakdown faults like a megger will.  The difference has to do with the non-linear behavior of insulation faults: they don't exactly follow Ohm's Law (current proportional to voltage) like a conductive connection does.  Compromised winding insulation may register as "inifinite" ohms (open) when tested with low voltage, but will "break down" and conduct when subjected to a greater voltage.

A fuse or breaker will most often trip on a wye connected transformer, however on a delta-delta connected transformer it will not trip, instead you will have one leg (on a 3-phase) with no or very little voltage and the other two phases (lest say its a 3 phase 480v system) would read 480 volts to ground rather than phase to phase. just thought I would point that out to all the troubleshooters out there.

Very good point -- ground faults don't blow fuses in ungrounded systems!  Thanks for the clarification.

Very good demonstration thanks

Thank you. Your explanation is very clear and helpful.

"Ground resistance" in a power system usually refers to the low expected resistance between the grounding conductor and earth ground.  This is different from insulation resistance which is expected to be very high.

Best explanation on youtube for this testing.

Thank You for the demonstration!

Halfway through I was saying "Such a fault would show up with a common DMM!". Ha!

Very good explanation of HV insulation testing and its value.

Still valuable 5 years on (and for as long as we'll be using induction motors...)

Very well illustrated and described. Thanks much!

Great explanation. Thanks!

Thankyou. Helps greatly with my studies.

That meter is a fantastic bit of kit, a generic copy of the Robin / kewtech from the 80s/ 90s. There now made by a number of manufacturers and use different brand names Fad demo and video

awesome learning. i have an interview soon! hope I do good.

A motor that shiny was either connected wrong or someone turned the overloads up...  Good video.

Thans you very much

Often, it will trip the overcurrent protection device (e.g. breaker or fuse) if the fault is phase-to-phase.  A ground fault on its own may blow the fuse or trip the breaker, but only if the three-phase power system is hard-grounded (e.g. a Y-connected source with the center point firmly bonded to earth ground).  

@nahroyo ....Thats fantastic! Your a star!