Do I need a megger?

[Rewire]

Good. Now dampen it. Drive a metal staple at that location and try again. You will not find every problem. Just most of the ones that will give you grief.

As a side note, I set a torch to the wire and tested it and the reading changed but after it cooled the reading was the same as the original I then completely burned off the coating allowed it to cool and the reading was the same as the original.

IMO using a megger to determine the safety of a circuit is limited and could be accomplished with a simple continuity tester.

 

[zog]

I have my fluke 1507 out i just tested a ten foot piece of romex I then gouged the wire with my strippers and I then tested again , results were the same.

What else would you expect? You are just measuring air resistance. The concern is the damaged insulation allowing the conductor to fail to something grounded. What would you expect your megger to read if you tested a power line on a pole? No insulation there.

 

[Rewire]

What else would you expect? You are just measuring air resistance. The concern is the damaged insulation allowing the conductor to fail to something grounded. What would you expect your megger to read if you tested a power line on a pole? No insulation there.

exactly the point i was trying to make.

 

[zog]

exactly the point i was trying to make.

Yes but you sure can not test insulation with a continuity tester.

 

[Rewire]

Yes but you sure can not test insulation with a continuity tester.

well actually if the insulation is damaged and bare wires are touching....

 

[wawireguy]

I got a call from a customer. They got caught doing work without a permit. The inspector told them to get a electrician to confirm that everything is safe.

Confirm? I would call the inspector. See if you could get by with inspecting all the make up and the panel. I'd also draw up some paperwork that you aren't responsible for the wiring. Just that what you looked meets code. Probably double the charge to the customer. You could get a megger or you could just flip the breakers on and see if they hold. Megger would be better. I wouldn't take full responsibility for their wiring.

 

[roger]

well actually if the insulation is damaged and bare wires are touching....

That would not be testing the dielectric strength of insulation, that would only be verifying the absence of insulation.

Roger

 

[zog]

well actually if the insulation is damaged and bare wires are touching....

Yes, if the wires are touching you can use an ohmeter, but to have a reading that has any meaning when measuring insulation, in the Megohm range, you need to use a Megohmeter.

 

[cadpoint]

Depends on the size of the leak. That is why you use the megger, to find those little leaks. Big leaks can be found with your continuity tester.

As a side note, I set a torch to the wire and tested it and the reading changed but after it cooled the reading was the same as the original I then completely burned off the coating allowed it to cool and the reading was the same as the original.

IMO using a megger to determine the safety of a circuit is limited and could be accomplished with a simple continuity tester.

Try another experiment with a knife and open up the insulation for half of the total length...

With the pull and twist of a circuit run there's no predetermined moment that say all will short to the conduit or another conductor...

Frankly, I'm thinking your forgetting what your testing...

 

[brian john]

We are often hired to inspect and test rooms after they have been sheet rocked.

We disconnect all conductors from the panel and megger everything, then we remove all devices and inspect every box and device, reinstall and megger again.

Check for compliance with applicable codes and workmanship.
Full notes
Full documentation
Lots of pictures

Typically well above normal rates.

 

[brian john]

IMO using a megger to determine the safety of a circuit is limited and could be accomplished with a simple continuity tester.

In any electrical testing the user of the equipment must (or should be)

Competent in the use of the equipment.

Understand the limitations of the equipment and the distribution equipment under test.

In all the years of using a megger (30-35 years) I do not know of any situations where I was not able to figure out the problem at hand, discern the issue or KNOW OF any situations that are often brought up as reasons to PooPoo the use of insulation testers.

That does not mean there are conductors out there in a PVC pipe or maybe in EMT somewhere, where there is a nicked conductor but if it tested OK it is OK, till such time as it faults and there is NOTHING I/we can do about that, unless you want to get into the realm of destructive testing or pull the conductors out after pulling them in for a visual prior to re-pulling them.

But I am sorry this statement shows a total lack of understanding of testing and the work involved. Now I have a certain prejudice but either my training or ignorance of something you know that I may not clouds my beliefs.

 

[ELA]

Took this from an article on insulation dielectric testing :

Test Voltage. If the test voltage is too low, the insulation material will not be adequately stressed during the test, allowing inadequate insulation to pass the test. On the other hand, if the test voltage is too high, the test could cause permanent damage to an insulation material that is otherwise adequate for the application. A general rule of thumb used for testing mains wiring that operates at voltages of 120?240 V ac is 1000 V plus two times the operating voltage. Using this rule, 120-V wiring would be tested using a voltage of 1000 V + (2 x 120 V) = 1240 V ac.

Sometimes insulation between conductors is compromised and you need the higher voltage of the megger test to apply stress to the material in order to aggravate the situation.
Often wiring insulation faults can be intermittent in nature. The megger is a tool to appy above normal stess to the insulation to help flush out a compromised situation (which may not involve actual copper to copper direct contact)

 

[wptski]

Took this from an article on insulation dielectric testing :

Test Voltage. If the test voltage is too low, the insulation material will not be adequately stressed during the test, allowing inadequate insulation to pass the test. On the other hand, if the test voltage is too high, the test could cause permanent damage to an insulation material that is otherwise adequate for the application. A general rule of thumb used for testing mains wiring that operates at voltages of 120?240 V ac is 1000 V plus two times the operating voltage. Using this rule, 120-V wiring would be tested using a voltage of 1000 V + (2 x 120 V) = 1240 V ac.

Sometimes insulation between conductors is compromised and you need the higher voltage of the megger test to apply stress to the material in order to aggravate the situation.
Often wiring insulation faults can be intermittent in nature. The megger is a tool to appy above normal stess to the insulation to help flush out a compromised situation (which may not involve actual copper to copper direct contact)

I think that rule applies to motors. Finding anything that applies to testing Romex is pretty hard, I've tried.

 

[Rewire]

In any electrical testing the user of the equipment must (or should be)

Competent in the use of the equipment.

Understand the limitations of the equipment and the distribution equipment under test.

In all the years of using a megger (30-35 years) I do not know of any situations where I was not able to figure out the problem at hand, discern the issue or KNOW OF any situations that are often brought up as reasons to PooPoo the use of insulation testers.

That does not mean there are conductors out there in a PVC pipe or maybe in EMT somewhere, where there is a nicked conductor but if it tested OK it is OK, till such time as it faults and there is NOTHING I/we can do about that, unless you want to get into the realm of destructive testing or pull the conductors out after pulling them in for a visual prior to re-pulling them.

But I am sorry this statement shows a total lack of understanding of testing and the work involved. Now I have a certain prejudice but either my training or ignorance of something you know that I may not clouds my beliefs.

I have always been taught never argue with a fool or try and put pants on a pig both are a waste of my time and although the fool may enjoy it the pig will get angry.

 

[George Stolz]

Rewire, I think you've stated your opinion clearly: you see no value in owning a megger.

Some (myself included) find that meggering even in it's least scientific application reveals clues about the wiring being investigated, which can prove helpful in various situations.

Your tone is bordering on belittling the users of meggers, which will not be tolerated. You can state your position without calling people that do not agree with you ignorant. Brian John has demonstrated his experience very well over the years, and spitting on that experience like a child will not degrade that. Knock it off.

 

[K8MHZ]

I think that rule applies to motors. Finding anything that applies to testing Romex is pretty hard, I've tried.

For troubleshooting I use 500 volts on Romex and have had good results.

The last time was an intermittent breaker trip for a water heater. When we arrived and applied power to the heater all seemed well and it was drawing proper current.

I shut off the power and got out the megger. I was seeing 2 to 7 million ohms from hot to neutral and a several million from neutral to ground.

To me, under 200 million is a fail.

The megger allowed us to take readings as we physically moved parts of the run of Romex. In just a few minutes we located a nail through the cable just barely touching the conductors, but had charred the surrounding area.

Newer DVOM's can read many millions of ohms, but that is at a very low voltage. For real tricky problems as well as simple verification, a megger is a must.

 

[zog]

Forget about "rules of thumb", you won;t find those in any current standard. Here is what the minimum test voltages and readings should be for non-inductive equipment.

 

[Rewire]

Rewire, I think you've stated your opinion clearly: you see no value in owning a megger.

Some (myself included) find that meggering even in it's least scientific application reveals clues about the wiring being investigated, which can prove helpful in various situations.

Your tone is bordering on belittling the users of meggers, which will not be tolerated. You can state your position without calling people that do not agree with you ignorant. Brian John has demonstrated his experience very well over the years, and spitting on that experience like a child will not degrade that. Knock it off.

George I never stated that I see no value in owning a megger you are putting words in my mouth. Please read for clarity. I never belittled those who use a megger so I have no idea how you draw that conclusion.
As for BrianJohn he appears to be grinding a personal axe against me but because he has great experience he gets a pass.
"
But I am sorry this statement shows a total lack of understanding of testing and the work involved"

 

[satcom]

For troubleshooting I use 500 volts on Romex and have had good results.

The last time was an intermittent breaker trip for a water heater. When we arrived and applied power to the heater all seemed well and it was drawing proper current.

I shut off the power and got out the megger. I was seeing 2 to 7 million ohms from hot to neutral and a several million from neutral to ground.

To me, under 200 million is a fail.

The megger allowed us to take readings as we physically moved parts of the run of Romex. In just a few minutes we located a nail through the cable just barely touching the conductors, but had charred the surrounding area.

Newer DVOM's can read many millions of ohms, but that is at a very low voltage. For real tricky problems as well as simple verification, a megger is a must.

Yes, a Megger is a great troubleshoot tool, we get to the problem fast.

 

[ELA]

Forget about "rules of thumb", you won;t find those in any current standard. Here is what the minimum test voltages and readings should be for non-inductive equipment.

Nothing wrong with "rule of thumb" values. As you stated your chart is the minimum.

Utlimately you have to refer to the standard you are trying to meet.
For instance UL864 section 74 states:


c) For circuits rated more than 150 volts AC rms (212 volts DC) – 1000 volts AC plus twice the
rated voltage (1414 volts plus 2.828 times the rated AC rms voltage, when a DC potential is
used).

Sounds just a little like the rule of thumb?