megohmmeter

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jcole

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Lawrenceburg, Kentucky
Hey guys and gals.

I see you guys talking about using megohmmeter to test insulation on conductors and windings on motors. I ve seen one used one time when I worked in maintenance troubleshooting a motor.

I ve had a good month and wanting to buy a new toy to become familar with. I understand that a megger measures resistance with a higher voltage than a normal DMV. I m guessing the theory is that a DMV does not have the "electromotive force" to push electrons through a real high resistance so current cannot flow therefore resistance reads infinite. Is this correct?

Some questions about meggers.

How do you know what the resistance should be on a certain wire or winding at a certain voltage?

How many of you have one and do you think it is a good investment?

Those of you that do have one what specs and fuctions should one have?

What types do you have and suggest?

Thanks.
 
I suggest sending a PM to "MDSHUNK". He is Mr. Meggar. I want one really bad also, but my hours have been cut back.

He mentioned some affordable models recently. He might know how well each one works.

I have only used the "old school" models which cost big bucks.
 
How do you know what the resistance should be on a certain wire or winding at a certain voltage?

How many of you have one and do you think it is a good investment?

Those of you that do have one what specs and fuctions should one have?

What types do you have and suggest?
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I WOULD NOT DO ANY ELECTRICAL WORK WITHOUT A MEGGER.

I like a megger that has a multi voltage function, 100, 250, 500, 1000.

I own 20-25 meggers and carry 5 on my truck a small handheld go no go tester 1000 VDC only, a 10-100 VDC tester for testing flooring, a 250, 500, 1000, 5000 VDC tester with timer, and a 250, 500, 1000, VDC crank megger.

Look at the Fluke web site.

PLAY with the megger, preferably without involving holding the test leads in your hands.
 
JohnJ0906 said:
This is what I have (and where I got it.)

http://www.professionalequipment.com/extech-autoranging-digital-megohmmeter-380260/megohmmeters/
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That's a good pick, right there. That will do probably 99% of what most guys might need it for up to 480. If you work with more than 480 on a regular basis, you might want something different. If you're doing some sort of official commissioning of switchgear and buss ducts, you might want something different. If it's for troubleshooting and to confirm your own new work (unofficially), this is a good pick for a good price.
 
jcole said:
How do you know what the resistance should be on a certain wire or winding at a certain voltage?
Click to expand...
This is the OP question that hasn't really been addressed (and that I'm particularly curious about)... Is the answer "play", as Brian suggests?
 
I think Brian is suggesting that you get use to the meter and know all it's peculariteis before you go to a job site. Taking numerous readings that indicate no problems when your $2 tester says "Yes, there is!!" is time consuming and embarrassing. If that every happens, put the lead in the other hole and blame your apprentice for setting it up wrong.
 
How I play with meggers:


Paper the thinner the better
#2 pencil
Varying amount of scribbles.
Megger at 1000 VDC
This does not always work the first time, gotta play with it or get a first grader to scribble for you (there big fat pencils have a real sot lead (CARBON).

 
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