Introduction to insulation testing using a Megger

In this video I go over some basics of what insulation testing using a megger is and what applications it might have for an inside wireman.

[rozerognh]

Great video! I just bought this meter and your explanation makes things clearer!

[awesomeelectricalengineer]

Good video. As others have mentioned, in the UK this would be correctly termed 'Insulation Resistance Testing', Megger is a brand name. Someone will correct me if I'm wrong, but I believe Megger made some of the first insulation resistance testers, hence the term 'Megger Testing' stuck. In the UK we insulation resistance test all new circuits as required by standard.

[slomotrainwreck]

Good video! I'm not an electrician but I do have my General class ham license and that's where I've seen people use a megger to test lengths of coax before installing it, it's the right tool for the job. 👍

[winner]

This is the best vdo. I always wanted to see this kind of test with explanation.

[theelectricianguy]

Awesome video, very knowledgeable information

[droodpvp]

Great video!! helped me understand this more! I do have a question that I believe this issue applies too, I dont know if you could help. I currently have an issue of a motherboard continually getting damaged and I believe it is the power coming in, but it reads a steady 120v. This is an outdoor application for an automated gate operator. It seems to run fine with no added features/ other wires connected to the system.

When I wire a 12vdc or a 24vdc plug in transformer to an outlet that is getting power from the same source as the operator, I have normal voltage on the power wires (12vdc or 24vdc). But the dry contact wires that should read no voltage actually give off 10-15v (ac) from wire to ground. I do not have a megger currently but will be getting one to test the incoming 120v power.

What you have described in your video sound like the incoming power is leaking voltage into the ground. Is it possible these wires that should be carrying no current are getting some AC voltage from the leakage? I have replaced the motherboard 5 times and the external devices 2 times and the communication wires 2 times. (Have not replaced or looked at the 120v line in the ground.

I hope this is understandable, I am just desperate.

[safetythirdified]

I will be using this to teach my class.

[Badtxv]

This is an awesome video I learnt some things thanks and good job man

[nlh]

I haven't used one in a long time. At work, they just bought a couple of the exact meter you have. Had a 50hp on an AHU, VFD going into earth fault. Started testing last night, and I diagnosed a bad VFD, this morning I'm told the motor is bad. Of course, I didn't see your video, I'm watching it again and I'll go up and do testing again, this time I'll be testing the wire to the motor and the motor. Is it possible wire with weak insulation causes the motor to short? we will see. VFD is isolated out of the circuit. It really helps me understand how best to use this meter. I was told the motor is bad if it tests below 100, I'm open to some input on this. Thanks, N.

[philipchristopher]

This video is very informative

Thanks

[Metal_seer]

I want to compare the resistance of different wire connections (twist and headshrink, twist, solder, and heatshrink, clamp, and solder seal). Can I do this with an $80 megohmeter and two wires, or do I need a $1000 + megohmeter or even 4-wire Kelvin bridge?

[markcummings]

Thank you, very well explained. Just curious. The greater than 1 MΩ acceptable reading, is it dependent on the cable, or voltage applied? Or no matter the case if I see this > 1MΩ I can confidently say the insulation is acceptable?

[danielclark]

When carrying out this test, would you keep the test button in until it equalises? I was told to just hold it and let go soon as you see a reading?

Your math is not correct. The insulation is mesured at 500V and not at 110V. Therefore insulation resistance is not same at 110V as at 500V and, consequently, leak current will be different at 110V.

[humz]

Just to add several things. While the Megger guide is good for understanding the theory, your better off using engineered standard in terms of numbers.

Ex. Neta standard has a 600v cable to be tested at 1000V and it should be a minimum of 100Mohms.

1000vdc megger does not damage 600v insulation, as it is non destructive for a short period, with very small amounts of current. Using the highest recommended test voltage is best to measure leakage current to test insulation resistance.

[mingovazquez]

Thank you sir, for great information 👍

[joetyrrell]

Not familiar with the process of using a megger. Was requested to do a megger test on all the circuits in a home that had fire damage. I just so happen to have just purchased this exact megger you are using in the video.

I'm surprised Klein does not have any kind of tutorial for this tester.

I found your video extremely helpful.


Thank you very much!

PS: do I need to test between hot to a grounded conductor / neutral to a grounded conductor? Or does the test work with none of the conductors actually providing a return path to the Earth (as you show in the video)?
Some videos seem to show tying the hot and neutral together, and testing between those and ground.

[LR]

I was taught to never megger anything at a voltage higher than the voltage rating of the insulation. You can cause insulation failure. When meggering a motor you can’t exceed the volts per turn rating of the motor.

[GOEA]

Megga is a brand that made some of the earliest elextrical resistance testers. Doing a megga test is the slang for testing the electrical resistance between two conductors. But I agree with @lewistreloar2312 it sis utter madness that you dont test your circuits before you commission them. In the UK we aslo test for the earth bonding impedance. Dont get me started on the lack of PVC sleeving on the earthing conductors and the worlks if issues not sleveng them can cause.

[lewistreloar]

This is is crazy that in the US you don’t use these everyday.
In Australia and most of the world it’s mandatory to use this on every circuit you do any work on.