megger question.

[weressl]

does anybody have or know where i can download and print some documentation that says using a megger is a good idea? im talking about something, for example, from an arc fault breaker manufacturer that mentions the use of a megger. i hope you guys know what im talking about

i know theres plenty of information on here i just need something i can print out thats from a major electrical equipment manufacturer or something like that

To aswer simply:

An Ohm-meter is designed to measure the conductivity of an electrically conductive element, such as wires, coils, windings etc. It is non-voltage dependent.

A Megger or (genericly) insulation tester is designed to test the resistance of an element that is designed to insulate/isolate electrically conductive elements form each others or from gound. It is voltage dependent as an element may exhibit high resistance at low voltages but reveals low resistance when it's designed operating voltage is applied.

 

[wptski]

Well first you are testing insulation with say hv 1000 volts between conductors its just a test to pick up a bad point say a pinhole or nick in the wire under test . at 120 volts you dont have the voltage to pass thur that pinhole in that insulation but over time even at 120 volts with age that hole will get bigger due to electrical conduction to ground and heat or dampness and just plain old life span of insulation it shorts . You dont have that problem at terminals because its connected to lower voltage a point of opposite polarity and also not enough potential to pass just randomly to any point . best to ya

That's like saying that if you stripped back the wire 5/8" over time it'll increase to 3/4".

Take a lenght of NM, megger it, put a pinhole/nick or whatever and megger it again. You'll see no difference at all

What if you suspended two "barely" seperated bare copper rods with the leads from a megger clamped to each one? What about meggering the ground conductor to one of the other conductors in NM? Does it fail? It should if what your saying is true.

In some cases with a very high DC/AC voltage megger, it may jump through a pinhole but it sure won't do it at 1000VDC.

 

[electricalperson]

if theres a pinhole in THWN wire pulled underground for example and water finds its way into the pipe, that pinhole will cause gfci's to trip and other problems.

heres a great example of that. we pulled in 500s for a 1200 amp service. the service was down on the docks right next to the water. the pipes went underground into the manhole we pulled the wires in and terminated them and the power company turned them on. when its high tide the manhole fills with water and so does the pipes, so in a few days we get a call from the marina saying there service just blew up we get there and the LB was blown to shreads and nstar is there shutting the power off. the other crew pulled the wires out and they were completly melted and destroyed. we think there was either a very small hole or nick that no one noticed when they pulled the wires in. this is a perfect reason why i stand behind using a megger.
i have to admit without mike holts forum i would never use one. brian john and mdshunk are the megger experts and they helped me out a lot

 

[wptski]

if theres a pinhole in THWN wire pulled underground for example and water finds its way into the pipe, that pinhole will cause gfci's to trip and other problems.

heres a great example of that. we pulled in 500s for a 1200 amp service. the service was down on the docks right next to the water. the pipes went underground into the manhole we pulled the wires in and terminated them and the power company turned them on. when its high tide the manhole fills with water and so does the pipes, so in a few days we get a call from the marina saying there service just blew up we get there and the LB was blown to shreads and nstar is there shutting the power off. the other crew pulled the wires out and they were completly melted and destroyed. we think there was either a very small hole or nick that no one noticed when they pulled the wires in. this is a perfect reason why i stand behind using a megger.
i have to admit without mike holts forum i would never use one. brian john and mdshunk are the megger experts and they helped me out a lot

You bet but that isn't what ohmhead stated somewhere above. They said that a pinhole or nick will get bigger over time and also can be detected by a megger at 1000V.

 

[electricalperson]

You bet but that isn't what ohmhead stated somewhere above. They said that a pinhole or nick will get bigger over time and also can be detected by a megger at 1000V.

well a pinhole in insulation wont cause a problem. if theres a path from that copper under the pinhole to another wire or ground or whatever then it wil lcause problems such as burning insulation. i tested this with my megger. i had a piece of romex with a little nick in it, threw some water on it and meggered it. you could see the arc coming through the nick to ground and it burned the insulation a little

 

[wptski]

well a pinhole in insulation wont cause a problem. if theres a path from that copper under the pinhole to another wire or ground or whatever then it wil lcause problems such as burning insulation. i tested this with my megger. i had a piece of romex with a little nick in it, threw some water on it and meggered it. you could see the arc coming through the nick to ground and it burned the insulation a little

Go back and read what ohmhead wrote. No water is mentioned at all.

You can probably get the same results by just dipping the a cut end of Romex in the bucket of water too. The end is like just a big pinhole.

 

[ohmhead]

wire in pipe & romex megging

wire in pipe & romex megging

Well the term pinhole is just a example like a cut in the insulation , i only do commercial or industrial work if you have a pinhole or a nick in a run of 750 mcm underground in pvc in a duck bank ,now copper will show a low megg reading and also alum wire but the alum wire will burn out faster then the copper, with out touching any other conductor to ground due to damp air or water or just age . Copper will last longer but it will fail also it does not have to have a contact with any other wire to do this it just takes longer to short out to ground . Also romex is run above ground mostly in a dry area if you had a pinhole in your romex you would never know unless you megged it . when insulation burns hot from current flow to ground that little pinhole blows up real bigg at 277 volts or 4160 volts thats just my thinking on the issue . best to ya

 

[wptski]

Well the term pinhole is just a example like a cut in the insulation , i only do commercial or industrial work if you have a pinhole or a nick in a run of 750 mcm underground in pvc in a duck bank ,now copper will show a low megg reading and also alum wire but the alum wire will burn out faster then the copper, with out touching any other conductor to ground due to damp air or water or just age . Copper will last longer but it will fail also it does not have to have a contact with any other wire to do this it just takes longer to short out to ground . Also romex is run above ground mostly in a dry area if you had a pinhole in your romex you would never know unless you megged it . when insulation burns hot from current flow to ground that little pinhole blows up real bigg at 277 volts or 4160 volts thats just my thinking on the issue . best to ya

A copper conductor is going to short to ground over time without touching anything or being wet? Are you kidding?

There is underground/wet rated, so called Romex. I believe it's NM-C, it's grey.

I agree that a pinhole, nick, etc. gets bigger when it melts and the stripped end gets longer too.

You need to get yourself a piece of Romex, megger it at 1000V, nick the heck out it and megger it again.

 

[ohmhead]

electrical trade commercial industrial

electrical trade commercial industrial

Well sorry Bill i guess i was not thinking romex ? Yes a pinhole in copper high voltage cable will fail with no water or connection to anything but air its called corona or tracking creepage . Next alum wire will oxidize it will actually form a powder of gray or white in color and the compact concentric strands inside expose to air inside the conductor will burn inside the insulation of that conductor do to just air in that pinhole high voltage conducts thur air no water no dampness no contact needed, it will burn out and short to any object close to ground or opposite polarity . I hope this helps you understand my post better and i wasnt kidding and there is other test on conductors and cables if your interested ? comments ? best to ya

 

[wptski]

Well sorry Bill i guess i was not thinking romex ? Yes a pinhole in copper high voltage cable will fail with no water or connection to anything but air its called corona or tracking creepage . Next alum wire will oxidize it will actually form a powder of gray or white in color and the compact concentric strands inside expose to air inside the conductor will burn inside the insulation of that conductor do to just air in that pinhole high voltage conducts thur air no water no dampness no contact needed, it will burn out and short to any object close to ground or opposite polarity . I hope this helps you understand my post better and i wasnt kidding and there is other test on conductors and cables if your interested ? comments ? best to ya

This is about meggering. You mentioned using 1000V several times and it would detect a pinhole. Doesn't matter if it's HV or LV cable.

Are you are refering to using meggers with a much higher output? Takes lots of energy to ionize air, like lightning. I was a ETN-3 in the Navy and seen a RM pulled a energized antenna patch cord. It drew a nice large blue arc!

I was told during my Navy days but don't know how true that you have to touch AC to get hurt but DC will come find you! There was a death while I was on ship where the ETN was using the Navy issue analog meter. It was on a 10KW tramsmitter and we had one also. As I remember the PA plate voltage was 7.5KVDC and that's what they were measuring. The meter was in the wrong range or something and they reached to change the range. Either leakage from the meter or the leads got them. Your never supposed to touch the meter while measuring HV like this, they should have powered down first. Seems like the meter had a seperate HV input and a 1X, 2X, 3X, etc. range. Long time ago!

If you have any links about detecting pinholes, nicks, etc. in any insulated conductors, I like to read them.

 

[zog]

I was told during my Navy days but don't know how true that you have to touch AC to get hurt but DC will come find you!

Nonsense

There was a death while I was on ship where the ETN was using the Navy issue analog meter. It was on a 10KW tramsmitter and we had one also. As I remember the PA plate voltage was 7.5KVDC and that's what they were measuring. The meter was in the wrong range or something and they reached to change the range. Either leakage from the meter or the leads got them. Your never supposed to touch the meter while measuring HV like this, they should have powered down first. Seems like the meter had a seperate HV input and a 1X, 2X, 3X, etc. range. Long time ago!

I remmember that incident when I was in also (EMC(SS))

 

[wptski]

Nonsense

I remmember that incident when I was in also (EMC(SS))

If that is "nonsense" then what "ohmhead" stated about a megger detecting a pinhole is "nonsense" too!

I think it was when they touch the selector knob.

So, what happened or what do you remember about the incident?

 

[ohmhead]

Well BILL whats your issue with a pinhole still dont think it can short out over time lets debate it now ? If you test romex you may find a ground to the hot or neutral with 1000 volt megger but may not if its not touching anything there inside that outer insulated jacket to me romex is a joke to even bother to test we were just trying to help the op asking about it , if you test a high voltage cable or conductor you use a high pot tester at what ever voltage the factory of that cable manufacture recommends . can be from 1000 volts in steps up to the limit of 5 times the rating of that cable or conductor , we test all the time were i work mostly high potin but lots of megging also we have dc and ac testers and when i was in the navy as em3 we used a high freq tester on cables to check for pinholes thats how i learned about pinholes in conductors and cables cvn-68 nimitz ? best to ya

 

[wptski]

Well BILL whats your issue with a pinhole still dont think it can short out over time lets debate it now ? If you test romex you may find a ground to the hot or neutral with 1000 volt megger but may not if its not touching anything there inside that outer insulated jacket to me romex is a joke to even bother to test we were just trying to help the op asking about it , if you test a high voltage cable or conductor you use a high pot tester at what ever voltage the factory of that cable manufacture recommends . can be from 1000 volts in steps up to the limit of 5 times the rating of that cable or conductor , we test all the time were i work mostly high potin but lots of megging also we have dc and ac testers and when i was in the navy as em3 we used a high freq tester on cables to check for pinholes thats how i learned about pinholes in conductors and cables cvn-68 nimitz ? best to ya

I agree with that partial sentence. Whatever helps to find a problem quicker isn't a joke. Still like to see something on diagnosing pinhole and nicks with anything. If this is something a megger or highpot does, I'd like to read up.

I only found this one using a PSD but nothing about a megger, highpot, etc.

AGC-11, USS Eldorado

 

[ohmhead]

High potting high freq testing

High potting high freq testing

well high potting is a common test we do on every job , we use high voltage ac or dc test sets .Example of test we start at 1000volts then we go up in 1000 volt steps each step is a 5 minute test , we look for micro amps charging or discharge time it tells us all about that cable and whats wrong with it , we look at voltage holding time and leakage during the 5 minute test ramping up in voltage can tell us if the cable or conductor is cut or just a pinhole , if its got a bad termination or boot or if its a leak in the loadbreak or internally shorted . but the best tester is the high freq tester at 20,000 cps 45,000 cps at high voltage say 50,000 vac it could find a pinhole in a conductor so small you could never find ever with any common tester.Sometimes its very important to test cables or conductors in a area of say a nuke plant or a area of high degree of you can not fail ever !! and the test is engineered & spec on this stuff is most important . Best to ya Bill i just learned this at work and in the military if i find a link ill try and post it .

 

[electricalperson]

well high potting is a common test we do on every job , we use high voltage ac or dc test sets .Example of test we start at 1000volts then we go up in 1000 volt steps each step is a 5 minute test , we look for micro amps charging or discharge time it tells us all about that cable and whats wrong with it , we look at voltage holding time and leakage during the 5 minute test ramping up in voltage can tell us if the cable or conductor is cut or just a pinhole , if its got a bad termination or boot or if its a leak in the loadbreak or internally shorted . but the best tester is the high freq tester at 20,000 cps 45,000 cps at high voltage say 50,000 vac it could find a pinhole in a conductor so small you could never find ever with any common tester.Sometimes its very important to test cables or conductors in a area of say a nuke plant or a area of high degree of you can not fail ever !! and the test is engineered & spec on this stuff is most important . Best to ya Bill i just learned this at work and in the military if i find a link ill try and post it .

i do believe a pinhole or break in the insulation of a high voltage cable could break down due to the corona effect of that high voltage to the shield. when we pulled in high voltage cable underground for a service we had to hi pot it as well. we had to test it at around 68,000 volts and one of the load break elbows broke because water got in it

any comments zog?

 

[wptski]

well high potting is a common test we do on every job , we use high voltage ac or dc test sets .Example of test we start at 1000volts then we go up in 1000 volt steps each step is a 5 minute test , we look for micro amps charging or discharge time it tells us all about that cable and whats wrong with it , we look at voltage holding time and leakage during the 5 minute test ramping up in voltage can tell us if the cable or conductor is cut or just a pinhole , if its got a bad termination or boot or if its a leak in the loadbreak or internally shorted . but the best tester is the high freq tester at 20,000 cps 45,000 cps at high voltage say 50,000 vac it could find a pinhole in a conductor so small you could never find ever with any common tester.Sometimes its very important to test cables or conductors in a area of say a nuke plant or a area of high degree of you can not fail ever !! and the test is engineered & spec on this stuff is most important . Best to ya Bill i just learned this at work and in the military if i find a link ill try and post it .

Now you mention a cut conductor or a pinhole. Both are/have a lack of insulation. What's the difference?

What happens if you tested new cable before installing which some require or so I've read here. Three, four or whatever conductors. One end is cut clean. You strip the insulation off the other end and apply thousands of volts. Won't the clean cut end show up as a fault, similiar to a cut or pinhole? Or do just know what to ignore and what to look for?

 

[electricalperson]

Now you mention a cut conductor or a pinhole. Both are/have a lack of insulation. What's the difference?

What happens if you tested new cable before installing which some require or so I've read here. Three, four or whatever conductors. One end is cut clean. You strip the insulation off the other end and apply thousands of volts. Won't the clean cut end show up as a fault, similiar to a cut or pinhole? Or do just know what to ignore and what to look for?

well one end of the HV cable will be stripped properly, (taking outer jacket off, twisting shield, twisting off jacket under the shield then cut the dielectric. the other end might have a loadbreak elbow on it, attach the hi pot tester accordingly and test. any fault should show up. if theres a pinhole it might not show up but let that water soak in the dielectric then it will show up.

 

[ohmhead]

Well we rap or seal the opposite end of cable under test we use just your standard plastic handy wrap that you put your sandwich in everyday its rated for high voltage if left open it will pass high voltage to ground thur the air ,you can hear it hissing . The other end the part that the anode high voltage test end has a special cap over the conductor end or terminal sealing it airtight. Then we test it in steps this can take on the average 45 minutes to one hour on each cable or conductor lots of fun, The milliamp current meter is the key you must watch it at all times you can actually blow out a cable thats good if you do not test correctly . Thats why we ramp up voltage in slow steps so we dont blow out a cable , milliamps running up high fast dead short to ground . milliamps leaking down slowlly holding and then we increase voltage slightly and if it bleeds down again its a cut , nick ,pinhole in jacket 90% of the time ,we pull cable out of raceway and run it thur a water tank off a roll to roll you use a standard megger at 1000 volts and guess what you fine nick, cut , pinhole . once a cable is pulled out it is trashed hv cables are not repaired its real expensive ,so i get paid well by my company . best to ya

 

[ohmhead]

testing hv cables

testing hv cables

Well i added another post to help Zog we never test before install of cables the factory does that we pull and terminate but we do not connect up to switchgear or transformers ,motors , parallel gensets ect ect yet . Then we test after all ends are completed with lugs or load brks , Its always done that way after all the stress on the cable has been thur you know its good . One thing i must add we always ground each cable for 8 hours after a test if you dont the next day you come to work and grab that cable you will be zapped big time . hv cable can build up a charge after a test there just like a capacitor safe grounding is a must . you can pour water on a bad cable and the part thats got a cut or nick or pinhole smokes when you fine it after you pull it out take care best to yas