Live Circuit Insulation Resistance Measurement

Probably blow a fuse....maybe nothing....it's not the volts that get ya, it's the amps....

Sorry to disappoint you but as far as I know, Meggers output very high voltage and low current, especially those fed from a battery. You would need a fairly high current to blow a commercial fuse.

I think a Magger cannot even break trough the isolation. We usually do that with a dielectric strength test.

They don't get a well deserved Darwin Award.

They pat themselves on the back while saying "Phew, that was close!"

Management writes them up for gross negligence and/or incompetence.

They get a pink slip in their hand instead of a red tag on their toe.

Guys,

in this forum at least we expect technical answers, no philosophy please.

this place is not a management forum.

Please describe what it says, either in the instructions or using a link to its manufacturer's website or in the transcription of the telephone call that has taken place with its manufacturer's Technical Helpline, for the specific piece of equipment in question, then. That would be technical enough.

How is the forum supposed to know the answer (rhetorical question - NNTR)?

If there is an expectation that any subscriber is going to make equipment enquiries about the original posted query other than the original poster, that expectation is unlikely to be satisfied.

Please do not use undefined plurals, like <...we...>; <...we...> does not exist.

In this forum we expect technical details, things like:

Make and model of megger, lacking that then details as to type such as crank, early transistorized, modern microprocessor based, etc.

Whether the circuit was grounded or floating,

Whether any breakers operated or alarms were tripped,

Any equipment damage or personnel injured, etc., etc.

It sounds like you're on a fishing trip to determine the root cause of an incident, and are trying to make the evidence line up with the facts. And I'm not management, but an engineer that has seen and investigated the scenarios in my first post, and more.

So very true, most of the digital meggers these days measure first, apply voltage later. They also tend to have high impedance sources so they CAN be relatively immune to careless operation. However, like you say, we're all kinda like Sgt. Schultz here.

Sir,

humble request : if you don't want to help in technically analyzing / sharing your knowledge & experience, you can just ignore the posts, its not mandatory to reply every question in this forum. hope you understand..

& thank you remaining others who have given their technical input to think on.

“A friend is one to whom one may pour out the contents of one's heart, chaff and grain together, knowing that gentle hands will take and sift it, keep what is worth keeping, and with a breath of kindness, blow the rest away.”

– George Eliot

Humility doesn't cut through the chaff here, only cooperation and and the desire to learn does. If you don't want to share your knowledge to help us in technically analyzing your problem, then you should continue asking open-ended questions while ignoring our requests for more details. Playing twenty questions won't keep our attention span. Hope you understand that many of us have been in exactly the same situation you are, so our BS filters are set pretty high. Best of luck to you.

Another couple of possibilities are that the perpetrator of this act, assuming survival of the individual from this experience, becomes either re-trained, or terminated.

My Megger flashes a warning that the circuit is live. I’ve never put it to the test

Another possibility is that the individual that signed the Permit To Work on the circuit in question becomes subject to disciplinary action.

I think it would depend on the type of megger used and whether the DC circuit is grounded at the supply. The best scenario is that you will get an erroneous reading.

http://www.electrical4u.com/megger-working-principle-types-history-uses-of-megger/

The LV DC protection operates when you connect the + and - together when trying to test the insulation resistance between live conductors and outer sheath (obviously). Depending on the short circuit capacity of the circuit a dangerous arc flash event may occur.

Testing + to - insulation resistance could result in any number of results to the circuit, the insulation resistance tester and the unfortunate user. Without detailed knowledge of the circuit and the insulation resistance tester all we can do is speculate.

This is not an issue generally however as only a competent person should be using the tester and they should know to ensure the DC circuit is dead before testing. If they cannot be sure (for some reason) they should be wearing appropriate arc flash protection gear.