megging readings

[zog]

The Megger brand has one that does 200A.

Hmm, looks like I will hitting the megger booth at the powertest conference.

 

[RHJohnson]

In this post I'm refering to where you made the Fluke comment.

Thanks Bill - I didn't know exactly what you had referred to - now I'll try to explain. I contracted my services to large engineering firms to do start-up (some refer to it as commissioning), on projects they designed - and were then built by various construction companies, - for the client.
It was my (and others) job to verify everything electrical was properly wired and tested prior to energizing. Nothing was energized except under our direction. Even vendor supplied equipment was completely gone through, inspected, tested and verified for proper operation. This start-up is so detailed that every wire, including field control wiring is verified and meggered back to the source.
Acceptance standards are those of the engineering firm. Test instruments are required to have recent calibration, and be suitable for the test being performed. Examples: insulation tests were required to be done with a megger suitable for the test, (no 3 minute or 10 minute PI performed with a hand crank megger.) Hi Pot testing of MV or HV cable may be done once - after that only a regular megger would be used. Some firms would not even allow the Hi Pot to be raised to the higher recommended test voltages.
Hand held multi meters were not allowed for those "initial" megger readings on 480 volt and lower motors/systems. 600 volt cable was meggered at the 500volt scale, sometimes at 1000 volt - depended on the engineering firm and the experiences they had. (Note I said experiences, - not experience)

 

[wptski]

Thanks Bill - I didn't know exactly what you had referred to - now I'll try to explain. I contracted my services to large engineering firms to do start-up (some refer to it as commissioning), on projects they designed - and were then built by various construction companies, - for the client.
It was my (and others) job to verify everything electrical was properly wired and tested prior to energizing. Nothing was energized except under our direction. Even vendor supplied equipment was completely gone through, inspected, tested and verified for proper operation. This start-up is so detailed that every wire, including field control wiring is verified and meggered back to the source.
Acceptance standards are those of the engineering firm. Test instruments are required to have recent calibration, and be suitable for the test being performed. Examples: insulation tests were required to be done with a megger suitable for the test, (no 3 minute or 10 minute PI performed with a hand crank megger.) Hi Pot testing of MV or HV cable may be done once - after that only a regular megger would be used. Some firms would not even allow the Hi Pot to be raised to the higher recommended test voltages.
Hand held multi meters were not allowed for those "initial" megger readings on 480 volt and lower motors/systems. 600 volt cable was meggered at the 500volt scale, sometimes at 1000 volt - depended on the engineering firm and the experiences they had. (Note I said experiences, - not experience)

The part of that post that I questioned was these statements: That reading is taken with a megger that is set on the 500 volt output - not with a fluke that would probably read that same cable in the gigohms. Engineering would never accept a megger reading taken with a fluke.

Your saying there that a Fluke will read ten times higher on the same cable! I find that hard to believe.

 

[roger]

The part of that post that I questioned was these statements: That reading is taken with a megger that is set on the 500 volt output - not with a fluke that would probably read that same cable in the gigohms. Engineering would never accept a megger reading taken with a fluke.

Your saying there that a Fluke will read ten times higher on the same cable! I find that hard to believe.

RHJohnson, I would also like to see an explanation to the ten times higher claim please.

Roger