Meggers!!!

[ptonsparky]

More stuff gets tested than some people think. While many installers have never used a megger, it is common to have a 3rd party testing company come in after they are all finished and do acceptance testing, which includes megger teseting. Grounding, transformers,cables, breakers, relays, etc... all get tested.

Most guys just don't see it because they are on to the next job.

:grin::grin:! We all live in different worlds or degrees of reality. I would venture a guess that more stuff does not get tested than some people think. Lucky if anyone checks for continuity before startup.

Admittedly this will depend on the size of a project.

 

[K8MHZ]

More stuff gets tested than some people think. While many installers have never used a megger, it is common to have a 3rd party testing company come in after they are all finished and do acceptance testing, which includes megger teseting. Grounding, transformers,cables, breakers, relays, etc... all get tested.

Most guys just don't see it because they are on to the next job.

I was lucky enough to be on larger jobs where the EC I was working for did the testing. Being the curious type, I was attracted to the means and equipment being used which led to me learning how to use it and working with it in the field. 90 percent or more of the electricians I worked with wanted nothing to do with it. In fact, when I was a fifth year apprentice I ran the conductor test crew primarily because no one else wanted the job. I was fascinated by it, especially using the hi-pot.

Part of the test crew's job was to make sure that all the conductors went where they were supposed to. If they didn't, we got to re-pull them. I quickly learned how to trace wire on that job.

I now have a box full of test equipment one of the EC's I work for calls my Voodoo Box. I'll bet 9 out of 10 electricians wouldn't have a clue how to use most of the stuff in the box.

The fact is, I am the exception to the rule. Also, there is no need for every electrician to know how to use every piece of diagnostic equipment as 99 percent of our work doesn't need it.

I also have an oscilloscope, several standing wave ratio meters, RF watt meters a field strength meter and a Geiger counter.

 

[zog]

:grin::grin:! We all live in different worlds or degrees of reality. I would venture a guess that more stuff does not get tested than some people think. Lucky if anyone checks for continuity before startup.

Admittedly this will depend on the size of a project.

Anything larger than a school will likely get tested, and I would not call a school a large project.

Would I expect a house to get tested? Nope, unless Zog is buying it, then it gets tested before I sign the papers.

 

[76nemo]

We're ALL different...

We're ALL different...

My initial response would be this is what seperates boys from men, but you're talking to someone who has never even used a tugger, or someone who knows how to set one up.
Most of us specialize in one or two things or another. I just find it sad that those who do heavy work still ask about the use of IRT's. There are certain men that can promise everything is wired to spec, and yet not know of acceptance testing.

In English terms, this is even done on appliances with PAT's.

Again, this just baffles me..........

 

[cadpoint]

I don't know why journeyman level peps don't know!

We all have our own travels and baggage. Some are drawn to the light, some just use the light, some can't find the light!

This Great County gives us freedom of choice, go ponder that for a while...

Me, I relish the knowledge, for my trivia mind...

 

[paulgarett]

I bought and used my first megohmmeter, a digital fluke, when I was required for a job to test a 480 volt, 25 hp well motor. Since replacing this well motor is expensive, the owner needed proof of the problem. Other jobs include: checking the insulation integrity of old, nasty residential sub-feeds, checking new 500 kcmil sub-feeders, and using it for fun to check for direct grounds or shorts. I would like to learn more about how to properly use a megohmmeter.
Please reply if you have stories about using a megohmmeter, suggestions on proper use, or any other importation information.
Thank you

 

[cadpoint]

There is plenty of history on this subject here on this forum and on the I-net.

Here's a link from this forum.

 

[jmellc]

I only briefly studied meggers. I did see them used to test large wire we pulled but I didn't get a chance to be in on the testing.

Most wire we install out & around is rated 300 volts or 600 volts. How do you put 1,000 volts on it without damaging it?

 

[iaov]

On two different occasions I have run into plant engineeers who did not know what I was doing with that funny little box with crank on it. They tend to be a tool of serious trouble shooting electricians, however I never fire up high Ia/big wire installs without megging em first!

 

[K8MHZ]

On two different occasions I have run into plant engineeers who did not know what I was doing with that funny little box with crank on it. They tend to be a tool of serious trouble shooting electricians, however I never fire up high Ia/big wire installs without megging em first!

Little? Mine is three times larger and much heavier than my battery powered meters. They are also very delicate. Drop one once and see if it still works. Just don't drop it on your toe.

 

[Heymanisth]

Megger everything that has the potential of "blowing up really good" before you throw the breakers. Another good practice is to wear a "blast suit" to protect yourself against arc flashes when flipping the switch for the first time also.

If no megger is available at the very least use a meter and check between all the conductors and the grounding . Just be sure to stand to the side wearing protective clothing when you throw the switch.

Many Electricians are killed or seriously burned each year from arc flash explosions.

 

[knoppdude]

Megger everything that has the potential of "blowing up really good" before you throw the breakers. Another good practice is to wear a "blast suit" to protect yourself against arc flashes when flipping the switch for the first time also.

If no megger is available at the very least use a meter and check between all the conductors and the grounding . Just be sure to stand to the side wearing protective clothing when you throw the switch.

Many Electricians are killed or seriously burned each year from arc flash explosions.

Very good advice to follow, nuff said.

 

[wptski]

I also have for the past 26 years worked for a shop that never has seen much less used a megger, I asked once if one could be added to our inventory and after looking up a price from the local supplier, was told we haven't needed one in all these years for that kind of money we don't need one now.

But my first experience with meggers was in industrial, and one of the best eye opener I had was when it was explained to me in how they differ from a regular ohm meter, was that if you take a set of contacts and open them about the thickness of a couple papers thick gap, and use a ohm meter, it would show all is fine, but put a 500 volt plus megger on it, and it will fail, as it would arc over, this is the same thing when you have lets say an underground feed to a post light, you ohm it out and all seems fine, turn the breaker back on and it holds, couple days later customer calls and complains the breaker is tripping again, now what happens that is so random?
Transient voltage spikes, these little spikes that motors and ballast tend to kick into the circuits can sometimes can be a few thousand volts, the bad spot in the cable starts to arc over and the current increases till it trip the breaker, but you go back there and reset the breaker and it resets, till the next inductive load is turned off, in this building or one down the street.

The funny thing is, if you would place a TVSS on this line, it probably would have never been noticed until the line totally fails, but a megger would have found it the first time.

Either this Air Gap Calculator is incorrect, I'm misunderstanding it or your using some really thin paper as it shows that 500V won't jump a gap over .002"?

 

[darrenh]

The reason we use a megger is because a multimeter has insufficient voltage to stress the insulation to cause a small current to flow inorder to calculate the value of insulation. In most modern insulation the insulation is in the gigohm range. A multimeter will read good when stressed at 9 Volts, but when 100, 500, 1000 or 5000 volts are impressed on the insulation it fails. The quality of the insulation is not based on the sensitivity of the meter but how well it stresses the insulation and how well the insulation responds to that stress.
I have been using a megger for over 30 years, the one item that many people who claim to know how to use it is not knowing what the guard terminal is used for. When I explain how useful this terminal is in troubleshooting circuits by using it to isolate various parts from the circuit under test, they find it a useful addition to their testing practices.

How is this terminal used in troubleshooting?

 

[wptski]

How is this terminal used in troubleshooting?

Good question and I would like to know myself. Found the following at the Davis site.

Some insulation testers have two terminals, others have three. As these are DC testers, two of the terminals are the + and -. The third (if present) is a guard. It does not have to be used, and many persons use insulation testers satisfactorily without ever employing the guard. However, it affords the operator an extra function for diagnosis of equipment problems. The guard is a shunt circuit that diverts leakage current around the measurement function. If parallel leakage paths exist, a guard connection will eliminate those from the measurement, and give a more precise reading of the leakage between the remaining elements. As an example, dirt and moisture on a transformer bushing will promote surface leakage between the + and ? connections, thereby bringing down the reading and possibly giving a false impression that the bushing is defective. Connecting the guard to a bare wire wrapped around the bushing will intercept this current, and yield a measurement based solely upon leakage through defects in the ceramic.

It is most important not to confuse the guard with a ground. Connecting the guard and return lead to the same element of the test item only shunts the current that is supposed to be measured, and thereby short-circuits the measurement function. When selecting a tester, consider the goals of testing (basic installation checks don't generally require a guard), the electrical composition of the items to be tested (motors and transformers can be tested for leakage between windings, with ground leakage eliminated), the possible effects of surface leakage (wire and cable can carry current across the surface, via dirt and moisture, as well as through the insulating material), and the degree to which results must be analyzed (are "bad" items merely to be replaced or discarded, or will it be necessary to localize faults for possible repair). Testers with guards generally cost a bit more than two-terminal models, so don't pay for it if it's never to be used. On the other hand, in many applications, a two-terminal model won't be imparting the full spectrum of information that can be accrued by insulation testing.