Megger question URGENT.

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tonyou812

tonyou812

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Location
North New Jersey
My buddy just called me on his way to a service call. An old lady ran over a transformer and power company wants an EC to megg out the wires before they fix it. He has a BM122 megger but a vague Idea on how it works. I personally dont have alot of experiance with them. Does he test it on 500 volts for a transformer servicing residential? And does he connect one lead to the copper and the other to the insulation? If all is ok he should have the same ohm reading on all the wires right? And lastly he needs to isolate the wires meaning turning off the main breaker and disconneting the neutrals? any help would be appreciated.
I am serching in the archives now but thought it would be prudent to ask for help too. Thanks people.
 
let me rephrase my question. If a little old lady ran over a transformer and the power company said they want the wires megged out before they repair what would the procedure be in megging out the wires to test for any isulation damage. All I know about the tester being used is its a BM122. and the transformer is servicing two or three homes. Any help would be greatly appreciated.
 
Just not the right people here right now.

I have only used a Mega a handful of times and the readings where given to others to make sense out of.
 
Around here the POCO owns those conductors, so I don't know why they need an EC....

I think you would need to disconnect all wires at both ends. For a 120/240 system, 500v should be OK - but I would test @ 250 volt 1st.
You connect leads to the copper, not the insulation. Test L1 to L2, L1 to N, L2 to N. (Just 3 conductors, right?)

Are you testing from XFMR to meter?
 
The conductors need to be disconnected at both ends. Seperate the ends opposite where you are testing.

Or, if he tests from the XFMR end, just pull the meter, and unhook the neutral - the line conductors should be isolated by pulling the meter.
 
Also, a disclaimer....

I do own and occasionally use a megger, but I do not consider myself an expert on it's use. I am still learning myself.
 
To check out a cable, it's pretty straightforward. Just disconnect it at both ends, and meg each conductor to each conductor at 500 volts for your case. Hot1 to hot2, hot1 to neutral, hot2 to neutral. You'll want to see over 100 megohms for each measurement. Simple as that.
 
mdshunk said:
To check out a cable, it's pretty straightforward. Just disconnect it at both ends, and meg each conductor to each conductor at 500 volts for your case. Hot1 to hot2, hot1 to neutral, hot2 to neutral. You'll want to see over 100 megohms for each measurement. Simple as that.
Click to expand...
Ah the proffesor has finally chimed in. Thanks Marc after a little scrambling thats pretty much what found out. But your confirmation gives it its final stamp of "OKness" thanks again brother....:D Kirk out
 
deenergize all conductors, remove from lugs at both ends (you can turn off all breakers etc, but if you want to just test conductors simplify the test by isolating them)

as posted, test all conductors one at a time, one lead to the conductor being tested, the other to a) if metal conduit, the pipe, then each other conductor (some guys gang the conductors and ground to pipe and ground to simplify testing conductors one at a time)

use ppe if the meggar is old (gloves), allow the wire to deenergize for 30 sec before testing the next wire (or follow manufacturer instructions)

write down the test value for each conductor to neutral, other conductors, neutral, ground, and pipe (whatever applies)

anything <1000 megohms is suspect (others will give you lower values which they consider acceptable)
 
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