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.
Hello. Sorry just seeing this now. There could be many reasons why you have a reading on the dry contact wire to ground. Without knowing more about the complete circuit, I would only be guessing at the cause. I hope you were able to figure it out!
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?
My experience and understanding is with systems up to 600v, you should be in good shape at that value up to that voltage at least. Above that voltage, I really can’t speak confidently.
Neta testing standards would fail anything under 100Mohm. Any cable in good shape should read well above the 5Gohm max reading of this meter. Anytime we see under 100Mohms, we know the cable insulation has been subject to damage and/or significant moisture. I have seen cables tests in the 1-2mohm range, that have caused intermittent trips during higher moisture periods. Alot of it is common sense. If it's a major distribution cable, error on the side of caution and adhere to engineered standards like NETA. Is it a 120v branch circuit for a plug? You're probably fine to leave a cable testing at a couple Megaohms for a long time.
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.
Yeah if you tied neutral and hot together, if that neutral was still bonded, they wouldn’t get an effective insulation test from either of those conductors to ground. So I’d assume they isolate neutral from its bond prior to performing the test. But the test can be done to look for leakage currents between any two conductors. Just be sure to isolate the conductors you are testing so that you are testing a current path thru insulation, and not other return paths. Good luck!
This is a video showing electrical students in the UK how to do an installation resistance test to BS7671, which are the UK electrical regulations. The test values may be different to those in the usa but the test process is the same. ruclips.net/video/Ek1u2RjQffU/видео.htmlsi=80VhNEjADdjD-5JQ
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.
Tested the wiring #4 going from the VFD to the motor just the insulation solid 4000 all 3 legs, Tested motor wirings 10-ish all 3 legs, tested motor to motor ground open. Looks like the windings are bad in the motor. So why the "Earth Fault " on the VFD. I think we still might have an issue with VFD.
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.
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.
I think I’ve seen some videos of European countries using them for inspections. Yeah I agree, for at least circuits of certain voltages, or were installed under strain.
It is common practice on annual maintenance on large chillers used in HVAC,to Meg all compressor windings, and all pump motors. It is also valuable tool for nuisance trips of GFI protected circuits, to detect small current leakage under operating voltage. I always taught megger testing in my HVAC classes.
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.
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.
So what you say is sort of right and sort of not. Insulation resistance, will remain constant, effected mainly by environmental effects such as heat or moisture. Application of a lower or higher voltage will not change the resistance, but it will result in lower or higher currents that could flow thru said resistor.
@@TheElectriciansGuild Resistance varies with the temperature of the circuit. Take a heating element and measure its resistance when it is hot, just as you disconnect it from power, then check it when it is cold. As the ambient temperature rises, or the wire itself becomes hot, the resistance rises because the copper electrons are farther apart. If the wire is cold, the electrons move closer together and the resistance is lower. I like the hand crank generator type meggers rather than the battery powered ones. DC voltage of 1000 volts will not be damage the insulation on 600 volt rated wire. Neither will it damage motors that are rated at 460. In fact you should test motors at twice their operating voltage. It says right inside the instruction book of my AMEC crank style meggers..
if insulation resistance was constant with voltage as you say, then why bother to measure at 500V, an ordinary ohm-meter would do@@TheElectriciansGuild
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.
Awesome video, very knowledgeable information
Glad it was useful :)
Great presentation.
Thanks 😃
This is an awesome video I learnt some things thanks and good job man
Glad to hear it :)
This video is very informative
Thanks
I will be using this to teach my class.
Great to hear!
Thank you sir, for great information 👍
Learned a lot. Thank you!
You’re welcome :)
10/10 !!
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.
Hello. Sorry just seeing this now. There could be many reasons why you have a reading on the dry contact wire to ground. Without knowing more about the complete circuit, I would only be guessing at the cause. I hope you were able to figure it out!
Thank you for the video
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?
My experience and understanding is with systems up to 600v, you should be in good shape at that value up to that voltage at least. Above that voltage, I really can’t speak confidently.
Thank you. @@TheElectriciansGuild
Neta testing standards would fail anything under 100Mohm. Any cable in good shape should read well above the 5Gohm max reading of this meter.
Anytime we see under 100Mohms, we know the cable insulation has been subject to damage and/or significant moisture.
I have seen cables tests in the 1-2mohm range, that have caused intermittent trips during higher moisture periods.
Alot of it is common sense. If it's a major distribution cable, error on the side of caution and adhere to engineered standards like NETA. Is it a 120v branch circuit for a plug? You're probably fine to leave a cable testing at a couple Megaohms for a long time.
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.
Yeah if you tied neutral and hot together, if that neutral was still bonded, they wouldn’t get an effective insulation test from either of those conductors to ground. So I’d assume they isolate neutral from its bond prior to performing the test.
But the test can be done to look for leakage currents between any two conductors. Just be sure to isolate the conductors you are testing so that you are testing a current path thru insulation, and not other return paths.
Good luck!
This is a video showing electrical students in the UK how to do an installation resistance test to BS7671, which are the UK electrical regulations. The test values may be different to those in the usa but the test process is the same.
ruclips.net/video/Ek1u2RjQffU/видео.htmlsi=80VhNEjADdjD-5JQ
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.
Tested the wiring #4 going from the VFD to the motor just the insulation solid 4000 all 3 legs, Tested motor wirings 10-ish all 3 legs, tested motor to motor ground open. Looks like the windings are bad in the motor. So why the "Earth Fault " on the VFD. I think we still might have an issue with VFD.
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.
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.
I think I’ve seen some videos of European countries using them for inspections.
Yeah I agree, for at least circuits of certain voltages, or were installed under strain.
It is common practice on annual maintenance on large chillers used in HVAC,to Meg all compressor windings, and all pump motors. It is also valuable tool for nuisance trips of GFI protected circuits, to detect small current leakage under operating voltage. I always taught megger testing in my HVAC classes.
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.
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.
Resistance is a constant.
So what you say is sort of right and sort of not. Insulation resistance, will remain constant, effected mainly by environmental effects such as heat or moisture. Application of a lower or higher voltage will not change the resistance, but it will result in lower or higher currents that could flow thru said resistor.
@@TheElectriciansGuild Resistance varies with the temperature of the circuit. Take a heating element and measure its resistance when it is hot, just as you disconnect it from power, then check it when it is cold. As the ambient temperature rises, or the wire itself becomes hot, the resistance rises because the copper electrons are farther apart. If the wire is cold, the electrons move closer together and the resistance is lower. I like the hand crank generator type meggers rather than the battery powered ones. DC voltage of 1000 volts will not be damage the insulation on 600 volt rated wire. Neither will it damage motors that are rated at 460. In fact you should test motors at twice their operating voltage. It says right inside the instruction book of my AMEC crank style meggers..
bro，simulations only.
if insulation resistance was constant with voltage as you say, then why bother to measure at 500V, an ordinary ohm-meter would do@@TheElectriciansGuild
Don't forget lead to ground, he doing lead to lead
I can't hear you😂
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.
It’s amazing that the entire USA isn’t on fire for not doing this! Eek gads! 😂