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Why a Megger? #40271 07/17/04 12:37 PM
Joined: Jun 2003
Posts: 1,143
DougW Offline OP
(Not the Brand Name "Megger", but...)

Re-equipping my truck, and the Wife asked if there was anything I needed that I didn't have before. Seeing my chance to buy some toys, (hehehe [Linked Image] ) I suggested a few things off the top of my head, and then told her I needed to think about some others.

Perhaps I'm showing the limits of my experience here, but, since we pride ourselves in continually learning, I'll ask the question. What's a megohmmeter used for?

I know the primary use is to check insulation integrity, but how often do you use one? What are the other uses? Will the $249.00 one work as well as the $1899.00 one for "basic" use? Do I need one for resi work?

Just need to satisfy my brain on this.

Thanks in advance,


Work Gear for Electricians and the Trades
Re: Why a Megger? #40272 07/17/04 01:16 PM
Joined: Mar 2004
Posts: 947
twh Offline
Maybe I'll show the limits of my experience, too. I have a cheap megger that I bought through ebay.

I've never used a megger on residential work. My main use is to confirm that a motor is good. Most ground faults in a motor can be read with an ohmmeter. Apparently they are a good tool for preventative maintenance, but I never get called until something has failed.

So, when the customer has a motor that they are going to install, or start, and I am asked to check it, I hit it with 500 or 1000 volts just to cover my ass.


Re: Why a Megger? #40273 07/17/04 01:59 PM
Joined: Apr 2002
Posts: 2,527
Bjarney Offline
An ohmmeter is effectively a low-voltage DC source, with measurement of current when the low-voltage source is applied to an electrical assembly—displaying resistance according to Ohm’s Law for the actual voltage and current.

Meg-o-meters are also resistance-measuring devices, but work at a much higher voltage, [250-5,000 VDC] to better stress insulation in an electrical assembly.

Meg-o-meter use often depends on policy of your employer or client. With experience, they can be indispensable for insulation testing.

Re: Why a Megger? #40274 07/17/04 03:00 PM
Joined: Aug 2001
Posts: 7,520
pauluk Offline
I wouldn't be without one. They're very handy for finding leakage on motor windings, as already mentioned, or testing for suspected moisture incursion, and so on.

Under British "code," an insulation test is also specified for all newly installed wiring anyway, so a megger is considered an essential piece of equipment here. Our "Regs." specify a 500V DC test voltage for all 1-ph 240V and 3-ph 240/415V systems.

I have a couple of portable meggers, switchable ranges and with test voltages from 25V to 1000V.

Re: Why a Megger? #40275 07/17/04 05:57 PM
Joined: Jun 2003
Posts: 1,143
DougW Offline OP
Thanks to all who've replied so far.

The only time I've ever seen a need in my usual work was the unusual case of submitting a bid for a buddy who was looking at buying a house that had been involved in a fire. Our mutual friend (a County AHJ) suggested hooking a megger to any conductors not removed due to obvious fire area involvement to "prove" integrity for house inspection by the insurance company.

Re: Why a Megger? #40276 07/17/04 06:20 PM
Joined: May 2002
Posts: 1,716
Roger Offline
Doug, I agree with the others, but I'll add that unless you're doing alot of big commercial or industrial work that would require the calibrated results of a high dollar meter, I would go with an economy meter of a good name or quality.

Tell your wife that you need a megger and an Ideal Sure Test with the AFCI tester.

Tell her that these two meters must work together. [Linked Image]


Re: Why a Megger? #40277 07/17/04 08:24 PM
Joined: Jan 2003
Posts: 1,429
LK Offline
We use the megger on every pipe job, today we megged the wires for a pool instalation, last week we megged a take-over job, we use it more for residential work then commercial or industrial.
Buy that megger, and use it, checking your installation is the way it should be done, as years have passed the just get it done attitude is a standard practice.

Re: Why a Megger? #40278 07/17/04 10:54 PM
Joined: Apr 2002
Posts: 2,527
Bjarney Offline

Re: Why a Megger? #40279 07/17/04 11:33 PM
Joined: Apr 2001
Posts: 507
golf junkie Offline
Besides the uses allready listed I use mine often for troubleshooting direct buried wire ground faults.

Re: Why a Megger? #40280 07/18/04 12:49 AM
Joined: Jul 2002
Posts: 8,346
Trumpy Offline
Bjarney and Paul said it all!. [Linked Image]
The Megger that I use has 250, 500 and 1000V ranges on it.
Like Paul said above, I would just stay at home if I didn't have a Megohm meter, a very useful and essential piece of kit, don't leave the house without it!. [Linked Image]

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