(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 ) 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,

DougW

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.

tim

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.

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.

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.

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.

Roger

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.

Some insulation-resistance testing references... www.netaworld.org/files/ItemFileA425.pdf www.avointl.com/common/documents/Diagnostic%20insulation%20testing%20by%20S%20Drennan.pdf www.avotraining.com/training/catalog/common_viewproduct.asp?product=121 www.aemc.com/techinfo/techworkbooks/ground_resistance_testers/950-WKBK-GROUND.pdf

Besides the uses allready listed I use mine often for troubleshooting direct buried wire ground faults.

Damn,
Bjarney and Paul said it all!.
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!.

If you're looking for a cool tool, a meg is fine if you use it.

But, another hip thing to have is a TDR!
(Time Domain Reflectometer)

I've had one for a while now, and find it very useful. Measures cable length, circuit in conduit, distance to open or short, finds hidden splices, and most have tone generators now.
http://www.megger.com/us/products/ProductDetailsBySubGroup.asp?ProductSubGroupCode=T101

I use it for general troubleshooting all the time now. Last time I pulled it out, I had a dead short in a really long circuit. Hooked it up, and it told me how many splices it went through, and how far away the short was. Count back 5 boxes, and 90', bingo!
----------------------

Helps in find ing loose neutrals too!

[This message has been edited by e57 (edited 07-18-2004).]

e57

That TDR looks like fun. I couldn't find a price. Any idea what they cost?

Real low end - $250 Numeric
low mid - $500 Numeric
mid - $1000 Graphical
High $5000 Graphical

They can only be of real use if they are graphical.

go to www.jensentools.com
search by brand for megger, or sphiser (ms?)

I did not see it mentioned but a megger can be used to measure ground electrode impedance. Do not think that is useful purpose for residential applications, since all you have to do is drive two rods and call it a day.

I agre with Roger, a Ideal Sure Test meter is a valuable tool indeed. It can find just about any wiring mistake or poor connections.

Thanks to everybody for the responses. I think I see one in my future!