How to use a megger

ourkid2000 · Post by **ourkid2000** » Sun Oct 28, 2007 5:24 pm

Anyone know how to use a Megohm meter to troubleshoot faulty wiring? I'm an avionics apprentice and people have suggested in the past to me that this is a useful instrument in finding damaged wires.

Anyone know how it is to be used?

flyboeing · Post by **flyboeing** » Sun Oct 28, 2007 8:30 pm

go from one end to the other.......check for continuty/resistance

tiny · Post by **tiny** » Sun Oct 28, 2007 9:57 pm

Also go between the wire and ground to make sure its open. Just make sure that both ends of the wire are disconnected from the circuit to avoid frying any componants.

Dust Devil · Post by **Dust Devil** » Sun Oct 28, 2007 10:39 pm

be sure to calibrate it each time by holding the ends and having someone push the button

Pratt Punk · Post by **Pratt Punk** » Sun Oct 28, 2007 11:04 pm

That was a stupid comment. He is asking a question on an instrument that can cause bodily harm.

Pratt Punk · Post by **Pratt Punk** » Mon Oct 29, 2007 7:43 am

"An electrical shock causing 10 milliamps of current to pass through the heart will stop most human heartbeats. Voltage as low as 35 volts DC or AC RMS should be considered dangerous and hazardous since it can produce a lethal current under certain conditions. Higher currents are even more dangerous"

"Use the time proven one hand in pocket technique while handling an instrument probe. Be particularly careful to avoid contacting a nearby metal object that could provide a good ground return path"

Be particularly careful when testing static dischargers on high metal platforms or ladders.

CID · Post by **CID** » Mon Oct 29, 2007 7:43 am

First and foremost, I’ll comment on Dust Devil’s comment. DO NOT DO AS HE SAYS. If you have any sort of heart condition the high voltage from a megger can kill you. There are many different types out there using voltages that range from the hundreds to the thousands. Don’t let anyone convince you that it’s safe because its “high volts but low amps”. Generally a healthy adult can handle a localized zap but a momentary zap across the chest of a few hundred volts can be lethal. You only need about 10 mA of current across the heart to kill you.

A megger is not a continuity tester and shouldn’t be used as such. It’s an insulation tester. Use it to check for a breakdown in wire insulation or very other very high resistance circuits where the high voltage won’t hurt anything.

Before using it, make sure all sensitive system components are disconnected from the wire. That includes any equipment that shares a bundle with the wire in question.

Use the appropriate megger. Don’t use one that will exceed the wire voltage rating. Don’t touch the wire bundle while you’re testing. You may be exposed to shock. It’s always best to refer to the AMM to see if there is a specific method for the system you’re testing.

Wire insulation can break down in many different ways. Sometimes chaffing against airframe can cause an intermittent short that a meggar can find for you. You can also get ground faults from water or carbon ingress. Especially for old neoprene and fabric wrapped wire or Kapton wire that has formed radial cracks.

Dust Devil, try to be a bit more careful in the future. It may seem like fun and games but remember we’re sometimes dealing with inexperience here. Your little joke could have cost someone their life.

ourkid2000 · Post by **ourkid2000** » Mon Oct 29, 2007 12:55 pm

Thanks for the replies everyone.......good info.

Do you need to have one lead on each end of the wire or could you just put one end on ground? What indications will the megger give you if you have a broken or chafing wire? A low resistance maybe (my question I guess is what consitutes a low resistance in this case)?

I've seen meggers used but only briefly..........do you really need to disconnect anything else within the bundle? I guess that makes sense if there's other broken wires but it seems like a pretty painful task considering some of the bundles i've seen in my short career.

Again thanks for all the help

tiny · Post by **tiny** » Mon Oct 29, 2007 1:19 pm

yes you must disconnect other systems in the same bundle because of the high voltage that a meger produces. If there are any sensitive componants connected to the wire bundle they could be damaged and because they may be part of a diferant system you may not notice the damage right away.

Hook on lead to ground and the other to one end of a wire. (disconnect both ends of the wire) Then test which will show whether there is a short to ground or a break down in the insulation.

ourkid2000 · Post by **ourkid2000** » Mon Oct 29, 2007 5:44 pm

I'll buy that. It makes sense.........sounds like good advice. No worries, I wouldn't go stickin' a megger on any equipment based on this discussion but at least it helps to understand the process.

6ftsnipe · Post by **6ftsnipe** » Mon Oct 29, 2007 7:35 pm

Dust Devil wrote:be sure to calibrate it each time by holding the ends and having someone push the button

Idiot--is that some type of Regina joke?

Pratt Punk · Post by **Pratt Punk** » Tue Oct 30, 2007 5:09 pm

It may be just a Sadomasochism thing. Meggers, maybe a strobe power supply, then the granddaddy.....IGNITION EXCITORS. Ya baby!

All kidding aside, ourkid2000 nice to see you asking relevent questions as an apprentice avionics guy. If I had to do it all over again, avionics would be my choice too. Sounds like you are serious about learning how to do things the right way. Thats important! Best of luck and remember, in the aircraft maintenance trade, its a never ending learning process no matter how much experience you may have.

twotter · Post by **twotter** » Thu Nov 01, 2007 12:06 am

Dust Devil wrote:be sure to calibrate it each time by holding the ends and having someone push the button

Come on DD, you are smarter than that. That is just plain dangerous.

tiny · Post by **tiny** » Thu Nov 01, 2007 7:59 am

Some people are just plan stupid. Somebody (boss) pushed the button on a ignition lead tester while I had a lead in each hand hooking them up, and my heart has never worked the same since. Don't joke about such things.

Akira · Post by **Akira** » Fri Nov 30, 2007 1:56 am

Dust Devil wrote:be sure to calibrate it each time by holding the ends and having someone push the button

Im sorry but i fuckin laughed when i read that.
Anyone who is to embarsessed to read the instructions or ask a fellow worker how to use tooling, and has to ask in a forum shouldnt be using it anyway.

Dust Devil · Post by **Dust Devil** » Fri Nov 30, 2007 10:09 pm

I forgot we are in the sensitive age of the taser. If anyone took what I said seriously they have no business being in possession of a megger. I will say they do hurt like a bitch. anyone who has worked on a line truck and forgot to put the key to safe after megging line will know what I'm talking about.

CID · Post by **CID** » Sat Dec 01, 2007 7:46 am

If anyone took what I said seriously they have no business being in possession of a megger.

I don't think there would have been as much backlash if the original poster stated that he wanted information on how to use a megger. Joking with an experienced guys is one thing. Giving a novice dangerous advice is another.

ourkid2000 · Post by **ourkid2000** » Sun Dec 02, 2007 8:32 am

"Anyone know how to use a Megohmmeter to troubleshoot faulty wiring?"

"Anyone know how it is to be used?"

Umm.......let's see.......well I've just quoted the original posts questions and I'm the original poster. I do believe I was asking for information on how to use a megger quite clearly.

CID · Post by **CID** » Sun Dec 02, 2007 9:00 am

Whoops, my bad ourkid2000. I meant to say;

I don't think there would have been as much backlash if the original poster HADN'T stated that he wanted information on how to use a megger.

The message is that someone (you) asked for help and information so there's a good chance that you didn't know.

Sorry 'bout that.

twotter · Post by **twotter** » Mon Dec 03, 2007 2:39 am

Wow, nice back paddling.

You must be a politician too.

You shit on him and then when proved wrong would not even admit it. You tried to spin it otherwise.

You have just proven yourself..

CID · Post by **CID** » Mon Dec 03, 2007 7:26 am

It was a simple mistake twotter. I acknowledged it and offered an apology. It's how grown-ups have discussions.

twotter · Post by **twotter** » Mon Dec 03, 2007 10:22 am

Did you read that in a book?

You would have been the first to jump all over someone for doing the same thing. Don't get all high and mighty on us now.. Oh, sorry I forgot, that's what you do..

CID · Post by **CID** » Mon Dec 03, 2007 11:03 am

You would have been the first to jump all over someone for doing the same thing.

Can you show me an example? Or is it just another unsubstantiatable claim that you pulled out of your ass?

MCRS · Post by **MCRS** » Mon Dec 03, 2007 3:04 pm

Twotter and CID do you work together, seems I see you both bad mouthing each other alot.
Just thought I'd ask.

CID · Post by **CID** » Mon Dec 03, 2007 3:06 pm

Twotter and CID do you work together, seems I see you both bad mouthing each other alot.
Just thought I'd ask.

Nope. It's much worse than that. We're married.