Need help with new megger

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mdshunk

Senior Member
Location
Right here.
Ed Carr said:
Again Marc how long do I hold
the test button for? I've had more detailed instructions come with
a toaster. I just want to make sure I do this right. Thanks, Ed
I've got to tell you that if you're doing some sort of paid and documented test, you're probably going to be doing it for one minute. In those cases, you'd be using a different sort of megger that will have a timer. In reality, for troubleshooting, etc., your number will let itself be known within a few seconds. Holding the button in longer will let you see if the number is trending bigger, smaller, or jumping around, which can be helpful in alearting you to the nature of the fault.
 

electricalperson

Senior Member
Location
massachusetts
Ed Carr said:
Marc,Thank you! Now to clarify.I have 3 wires leaving the panel.
One hot,one neutral and the ground. I can test between the hot and
ground or the neutral and ground correct? To test between the hot
and neutral I have to disconnect at both ends. I figured I could smoke
the ballasts with them still in the circuit.Again Marc how long do I hold
the test button for? I've had more detailed instructions come with
a toaster. I just want to make sure I do this right. Thanks, Ed
test for at least one minute. a stitch in time will explain in detail about this

the insulation needs about 1 minute or so to charge completly before you get a reading. usually good insulation starts a little low and will slowly rise in resistance over the one minute test.

ive tested romex with my 1507 and it started at about 2000 megaohms and rose to about 9.6 gigaohms in about one minute
 

mdshunk

Senior Member
Location
Right here.
electricalperson said:
ive tested romex with my 1507 and it started at about 2000 megaohms and rose to about 9.6 gigaohms in about one minute
Since the accuracy on the 1507 is +or- 10%, I'd call 9.6 as good as "full scale". You'd certainly expect full scale readings on new cable.
 

Ed Carr

Senior Member
Location
way upstate NY
Well I guess maybe a good hands on start would be to
head out to the shop with my 1520 and try it on a piece of
romex.I should strip the insulation attach to the white and black
then hit test? Can I go from either insulated conductor to the
bare ground?
 

electricalperson

Senior Member
Location
massachusetts
mdshunk said:
Since the accuracy on the 1507 is +or- 10%, I'd call 9.6 as good as "full scale". You'd certainly expect full scale readings on new cable.
so are you saying analog insulation resistance testers are better? if so i agree with you. i like seeing the needle moving around and you can see stuff happen that you normally couldnt see with a digital read out. i like the features of the 1507 a lot
 

electricalperson

Senior Member
Location
massachusetts
Ed Carr said:
Well I guess maybe a good hands on start would be to
head out to the shop with my 1520 and try it on a piece of
romex.I should strip the insulation attach to the white and black
then hit test? Can I go from either insulated conductor to the
bare ground?
you attach the red/positive/earth lead to ground and you attach the black/negative/line lead to whatever wire you want to test

lets say you want to test the insulation of the black conductor to ground. you attach the black wire from your megger to the black conductor and the red wire to the bare conductor in the romex and hit test. if you test between the white and neutral you can attach the leads anyway you want. just make sure when you test to ground you hook it up right
 
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Ed Carr

Senior Member
Location
way upstate NY
Okay ,I went out to the shop and grabbed what I think
is an extension cord in good condition.It's a fifty foot 14/3
SJ.Put the red clip on the ground pin black on neutral pin.
At 250V got >1000, at 500V got >2000. I got the same readings
going from the ground to the hot pin. When I put the clips on
the hot and neutral pins I got 116mohms @250v and the same @
500v.What did I just find out? Thanks, Ed
 

electricalperson

Senior Member
Location
massachusetts
Ed Carr said:
Okay ,I went out to the shop and grabbed what I think
is an extension cord in good condition.It's a fifty foot 14/3
SJ.Put the red clip on the ground pin black on neutral pin.
At 250V got >1000, at 500V got >2000. I got the same readings
going from the ground to the hot pin. When I put the clips on
the hot and neutral pins I got 116mohms @250v and the same @
500v.What did I just find out? Thanks, Ed
the insulation of the neutral conductor is at full scale so thats ok, the insulation on the hot conductor is a little weaker than the neutral (probably from being stressed by high amperage) but its still ok, usually anything under 100megaohms might be damaged and you should investigate. if the resistance reading was lower at 500volts you would possibly have moisture or dirt or another type of problem with the insulation and should be watched.

testing at a low voltage then at a higher voltage and comparing the two readings is called a step voltage test
 

Ed Carr

Senior Member
Location
way upstate NY
Back out to the shop and this time tested a piece of
1/0 SO cord 3 conductor.Tried various combinations
with the leads from hot to neutral, hot to ground etc.
This time the readings were all the same.At 500v And 1000v
the scale would climb to max.Is this the absortion affect?
Me again
 

electricalperson

Senior Member
Location
massachusetts
Ed Carr said:
Back out to the shop and this time tested a piece of
1/0 SO cord 3 conductor.Tried various combinations
with the leads from hot to neutral, hot to ground etc.
This time the readings were all the same.At 500v And 1000v
the scale would climb to max.Is this the absortion affect?
Me again
im pretty sure if you megger something it normally starts out low then slowly rises to the correct measurement after 1 minute or so of testing. dont worry what the reading is at the first few seconds of testing. the reading after 1 minute is what you are looking for
 

zog

Senior Member
Location
Charlotte, NC
electricalperson said:
im pretty sure if you megger something it normally starts out low then slowly rises to the correct measurement after 1 minute or so of testing. dont worry what the reading is at the first few seconds of testing. the reading after 1 minute is what you are looking for
There are 3 different currents that you are measuring using a DC source, after about 30 sec the absorbsion current should start to decay and be gone at around 60 seconds, then you just have leakage current and polarization currents left, in non inductive equipment polarization current is negligable so 1 minute should be long enough, however for inductive equipment it should be a 10 minute test.
 
L

Lxnxjxhx

Guest
1520

1520

This megger seems to be the equivalent of a 1000v source in series with a 1 megohm resistor, with the meter reading current through the load or voltage across the load, and converting this reading to a resistance value.

At 1 mA max current, you should barely notice a shock from this thing (10 mA = painful, 100 mA = possibly fatal) but I guess there still ways you can get zapped using it.
E.g., between 1 and 50 joules of energy can be fatal. Joules = (1/2)xCx(V^2) so a 2 uf capacitor charged to 1 kV = 1 joule.
Cardiac defibrillators go up to about 10 joules.

Cuidado, senor!
 

ptonsparky

Senior Member
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
Electrical Contractor
Normally you would think pvc conduit would mean the conductors would be isolated from ground or earth. Your conduit is buried so most likely it has water inside which also means a test to earth can be done. We have found and repaired faulted conductors in PVC that showed up with an initial 3 volt Greenlee test. Obviously your Fluke will do the job.

When the length is 1500 feet of 250MCM Al, yes it is worth the splice.
 

Ed Carr

Senior Member
Location
way upstate NY
Would any of you members that have experience with
one of the Fluke insulation testers such as my 1520 be
interested in giving me a pm with a # I could contact
you at? I basically am just looking for some information
on the proper use of this tool and what is possible with it.
I have been to the Fluke users site and see quite a few
familiar names there.Any advice would be greatly appreciated.
Thanks, Ed
 

mdshunk

Senior Member
Location
Right here.
electricalperson said:
so are you saying analog insulation resistance testers are better?
No, I haven't said that at all. They might be, but I plainly don't know. I'm not so sure you'd have too much credibility in the eyes of a customer using analog equipment. They want to see digital stuff for the mere perception of high-tech. The one's with the hybrid display are nice for observing a trend. They have an analog scale, but it is on the digital screen, if that makes sense.
 

acwservices

Senior Member
Location
Eastern NC
Any recommendations on where to purchase a Fluke insulation tester? I know I can purchase one locally at my supply house or Grainger, but is there a place that may sell it at a better price?
 

acwservices

Senior Member
Location
Eastern NC
BTW, I just saw that with this post I have "graduated" from a Junior Member to a Member- is this kinda like going from a helper to a mechanic, or a green helper to a helper?
 
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