How to Test Wire Insulation Using a Megohmeter
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- เผยแพร่เมื่อ 4 ก.พ. 2019
- Chris shows you a quick and easy way to check your submersible wire. It's a good idea to check wire before you install (or reinstall) it into a well, and it only takes a couple of minutes!
To conduct the test, submerge the cable in water. While submerging the cable, make sure to keep both ends of the cable dry and out of the water. Since air acts as an insulator and water is partially conductive, if there is a breakdown in insulation in the wire cable, electricity will leak into the water and can be detected by a megohmmeter.
Place one probe in the water, and another probe on one of the ends of the wire. The readings should result in very large numbers. If not, the electricity is being leaked into the water, likely from a nick in the installation.
So, what’s a high ohm reading?
With the megohmmeter set to either 500 or 1000 VDC output, normal insulation resistance readings for drop cable and a motor (if attached) should read two-million ohms or more. If the reading is below two-million ohms, it is not recommended to use this wire. Reference Franklin Electric’s AIM Manual as needed for insulation resistance readings.
Link to Franklin AIM Manual: www.franklinwater.com/more/ser...
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Yet another golden nugget of information to use in my tool kit. Thanks for sharing!
I found this most informative. Thank you for sharing.
I've been an electrician for years now. The last time I used a Megger was when I was in school. And today I have to test some wires in a building.
Your video refreshed my memory. I'm good to go now.
Thank you ! 😀
Woohoo! Happy we could help :)
What about a standard multimeter?
It can go up to 10mohms or more.
@@irishguy200007 a multimeter is acceptable for testing circuit resistance (although a proper micro ohmmeter is preferable). You want high voltages for testing insulation, whereas a multimeter tests at something like 1.5V.
I'm an electrician as well and I always megg wires and motor winding but I use the fluke 1587 fc, which is way better
Great video, thank you for taking the time to create it! 👍👍
Glad you liked it!
I worked for an electrical testing outfit years ago and we tested everything in a power plant, anything from MCC switchgear, transformers, relays, high voltage busses, etc...One point I recommend in your video is try explaining where do you connect your negative lead and why? Also, explain why you should ground (short out) your positive lead to ground after each test? Megger wiring test plans can vary between many applications so, I would try to explain how a valid megger test only exists when you have an open circuit to the difference in potential between your test cable and ground. Other than that I thought your presentation was really informative.
Thank you ! Very informative.
thank u so much for sharing a good information love from india
Thanks for sharing this great knowledge
My pleasure
Thank you for the video, I have a question that I hope you will answer me, if I want to check the house cables from the board, what should the resistance of the wire be with respect to 500 volts, and how can I know if I have a problem with insulation. Thank you
Excellent video - Thanks
Glad it was helpful!
Great information! Please send us testing an induction motor with a unit of burnt motor and a working or serviceable motor in comparison...thanks and great info.
Now that would be a great use for it.
Great video
Thanks for the visit
very nice sir
Very Useful !
Glad it was helpful!
Good video.
Glad you enjoyed it!
Thanks for sharing
Thanks for watching!
Big thumbs up
Awesome
good video, one question, how should you select the correct voltage to be used on your meter ? thanks
I good rule of thumb I was told was to double the line voltage .. 120 v send 250 ' 240 volts send 500, 480 send 1000..
Im not the brightest bulb on the tree..please help me understand this test. Im at the well with all the leads disconnected from the source. Do i put one lead on the ground and the other lead on each wire during the test. Thanks
What is the numbers should get it when there is some leak? Thanks.
Thanks
thank you !
You're welcome!
Is that single insulated cable ?
Great and informative video. Thank you. I have a hurried wire imbedded in asphalt. How would I be able to determine the specific location of damage to that wires insulation. I have a tracer unit allowing me to determine where a break is but it is less than helpful with damaged insulation. Your input is appreciated.
He said u can spend weeks and still won’t find it bc the damage to insulation can be very minimal to the point where u can’t even see it
*I was in a Houston restaurant once and the line chef used something like you shown to test the soup in a giant pot, strange huh?*
Thanks for sharing, but what if you want to test insulation in wire that is not submersed. I have 3 600 mcm wire in a metal conduit. I want to be 100% sure before energizing that no insulation is nicked or compromised. Would I just attach one lead of megger to the insulation and the other to conductor? I want to rule out any possibility of having parallel arc fault.
Then test between the different wires, live, neutral, ground, as you are basically testing 2x insulation at any point there could be a short between two wires. To test the jacket it it's entirety, I guess you are supposed to submerse in water, because you can't get your meter probe to the wire later on - but in your instance you would attach the probe to the metal conduit of course :)
Now my question is, how do you test to see if the flow of current is flowing through the wire properly and that the internal conductor itself hasn’t been damaged, Wich from my understanding is that I can test with my Megger at a 1kv and max out at 2.2 gigaohms and there is times I can test and get a slow rise of 100 megaohms to 3 or 400 megaohms
Isn’t there going to be a pump ground wire to the casing, which is in contact with the water.?? Why not use that as your grounding reference.
If i were to carry out this INSULATION test on the table where would the test leads be placed then (if we are not placing one test lead in the water) . Do you just put the test leads on both ends of the wire youre testing or do you only use ONE test lead for the wire youre testing . Please advise
You cannot do this test without submersing the wire in water; because the water is conductive it will allow electricity to pass through it into any cracks in the insulation. That's why you have one lead on the end of the wire and one in the water.
@@RCworstwater What if i bought a new cable from the hardware store and its on a table rolled up new. Could i not check and test it to make sure the the insulation is good without unrolling the whole roll of wire. Could i then find the ends of the wire and test with the insulation resistance tester to make sure it does not have any cuts?
So... wouldn’t you want to check insulation resistance between each conductor as well?
Not necessarily unless the job spec requires you to. Theoretically If each conductor holds the voltage for x amount of time required in your test then that conductor has no damage to its insulation.
curious if salt water would make a difference over say distilled or ordinary tap water?
Demonized water is a non conductor. Utility companies use it to wash off insulators that are carrying high voltage electricity.
If anyone could help, I been looking for anything saying if Megger readings before you run the unit “cold readings is supposed to be more or less than the megger reading after you ran the unit for some time “hot readings”
You should ways Meg motors qt twice their operating voltage, and at operating temperature. Of course disconnect power first. Resistance in wire goes up with an increase in temperature, and down with a decrease in temperature.
You can do this in open air!!!! For every single wire you want to megger. Get a spool and connect 2 leads and megger.... that meter gives you the number of resistance. Wow....
We are measuring the integrity of the plastic insulation. Hooking one lead up to either end of the wire would tell you the resistance of the wire, not the insulation.
hi sir can an insulation tester detect wires if the wire's insulation is cracked but not touched each other.
like some old cables' insulation cracked and the cooper conductor exposed but not touching each other?
Yes. The high test voltage is enough to create an arc between the breaks in the insulation if the breaks are close but not touching. Any moisture would also make a difference.
How to megger without water?
So if I put the meter on both ends of the same wire, I should get a low value right. Like zero?
Correct
OK, but typically in a well case, the water level could be 20ft or more from the top. I think it's important to emphasize you need to drop some sort of test wire down there to hit water and then hook up one of the megga leads to that?
Just use the pump ground wire as your reference. It’s attached to the casing, which is in contact with the water.
There’s no resistance in water whether you’re at the top of 100ft or at the bottom unless it’s really really dirty and filled with junk like wood
Can these be used with fuel ?
Conspiracy theories aside, that is basically what brought down TWA flight 800.
I thought you were going to test the pump insulation and splices.
so no resistance means the wire is cut, resistance means the wire is ok? is 1000 volts ,who resist this voltage the wire or the insulation.
sorry for a dumb question.
I kissed where you put the other lead I just d at the red lead was the other end in the water?
I have a problem with my water well cause its keep tripping the breakers i have change the pressure switch and the control box its wokst until the pressure drops to 30 psi when it tries to raise the pressure tripping the breakers again
Jairo: Please give us a call and we will help you troubleshoot: 855.329.4519
why u got water down there...
That's where we like to keep it.
Just kidding, that's our pump testing pit.
Why would you read less resistance/ohms when the wire is damaged but hire resistance at 660 when it's perfect wire? Or am I just thinking about it in the wrong way. Are you sending 660 volts through the wire or something and if it's perfect wire it'll read 660 obviously, if it's bad wire the voltage won't make it's way through it and will read 0, is that what's going on? Also if you have one meter lead in the water and one touching the good wire and it reads 660, how does that lead that is touching the wire know that it's 660? The other lead is in the water so how does it know... Also let's say you have a panel and the main is tripping maybe every 3 or 4 hours. The customer calls you to the house but it doesn't trip right away. You want to do an insulation resistance test like you are doing now. How would you achieve this in the panel? You would go hot to neutral correct? Instead of hot to water like you are doing here.
@Castlebury21 reading 0 indicates there is no resistance and the wire is bad? How does this make sense. If there is no resistance, wouldn't it be a good wire? A bad/damaged wire would have a lot of resistance on it I'd assume
@@DJayAce4 take a electronics course you dick pickle
We are measuring the continuity between the water and the bare copper wire Jason, so no resistance means there is a crack in the wire insulation that would result in a ground fault if it were installed in a well.
@@DJayAce4You aren't really understanding what he is doing and why. In the test he is doing, he got 0 resistance between the copper conductor and the water thus proving that the insulation is compromised. Electricity is making a direct path from the water to the copper and vice versa through the damaged insulation. He isn't measuring the resistance of the 2 ends of one conductor. That would be done with an Ohmmeter and the resistance in a good conductor would not be 0 Ohms necessarily, but the lower the better. Depending on the gauge of the wire and how long it is will change that reading.
Muy mala la traducción. No se entiende. Por favor mejoren la traducción o si es posible pongan el audio en español pero con la traducción mejorada.
What did he saaaay?!😮
C
The proper word is submerged not submersed the way you are applying the word.