insulation testing

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Charlie Bob

Charlie Bob

Senior Member
Location
West Tennessee
got my fluke 1587 advance troubleshooting kid this week.
I'm gonna start getting used to this testings, but tell me if im correct, please.
1--If i'm to meeger a circuit with 5 receptacles, for instance, I disconnect the load side from breakers,(Everything that is plugged in, and disconnect hot wire from breaker, white from neutral bar, and groun from ground bar.)
Then can i run the test with the five recep.in the circuit, or should i disconnect circuits ?
2--If i disconnect recep. can i wire nut wire together and then test.
3--If the insulation test measures resistand along the insulation, showing weak points where insulation is damage or non existant, how does the terminals on the recptacles affect the test?
4--What can i do to start getting used to it?
Plase i appreciate any ideas>
 
ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
1. Yes, you can test with the recepts in the circuit
2. Yes, you could use wirenuts & test
3. The terminals will only affect the tests if they are compromised in some way. Dirt, moisture, insects, paint. Lose connections won't show up unless they have deterorated to the point of destuction at the device.
4. Use your house as a lab. Check the furnace motor. Drive the significant nuts with opened boxes and circuits under test.
 
K8MHZ

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
ptonsparky said:
1. Yes, you can test with the recepts in the circuit
2. Yes, you could use wirenuts & test
3. The terminals will only affect the tests if they are compromised in some way. Dirt, moisture, insects, paint. Lose connections won't show up unless they have deterorated to the point of destuction at the device.
4. Use your house as a lab. Check the furnace motor. Drive the significant nuts with opened boxes and circuits under test.
Click to expand...

Exactomundo!!

I have three megohmeters. One crank and two battery powered ones. One is your basic Biddle and the other is a beautiful old Sanwa.

Test the output with a volt meter. I you ever have to use a hand cranker you will be surprised at how much human energy it takes to get the thing up to 1000 volts. Then keep going for 30 seconds to a minute?? Doable, but not as easy as one would think.

Using a resistor with a known value (I use 2 megs) test the accuracy of the meter. I was surprised at how close all three of my meters were for this test as well as the voltage tests. (The hand cranker is the only one that get 1000 volts)

Either test or take out the batteries or risk losing your meter. My Sanwa had deteriorated batteries in it when I got it and I had to make some repairs. Nothing horrible, but I could see that over time the meter would have been toast.

Play around checking out what moisture does to your tests. Test water. Start with purified water and then add some salt to it.

Once you get used to the feel of your meter you will nearly instantly be able to detect a fault just by sensing that the needle movement is not right for instance.

And be careful. Even the little 500 volt rigs can give a person quite a jolt. I know that from a test I will refrain from recommending.

:roll:
 
Speedskater

Speedskater

Senior Member
Location
Cleveland, Ohio
Occupation
retired broadcast, audio and industrial R&D engineering
Marky, where did you get high voltage rated resistors? Most resistors are only rated at 200 or 300 Volts. Or did they come from the HAM radio shack?
 
K8MHZ

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
Speedskater said:
Marky, where did you get high voltage rated resistors? Most resistors are only rated at 200 or 300 Volts. Or did they come from the HAM radio shack?
Click to expand...

I just used regular old off the shelf ceramic 1 watt resistors. Two 1 meg in series.

They handle the voltage with no problem as they are not mounted, the test is only for a few seconds and the testers put forth very little current.

The voltage rating means that the resistor can handle the rated voltage continuously at full power mounted on a PC board without degradation or arc-over.

Please note that conductors rated at 600 volts are tested at 1000 volts. That said, there are many in the field that consider this to be 'destructive testing' as the possibility of damaging insulation, particularly old insulation, exists during testing. I have worked in old factories where megging existing conductors was not permitted.

There are other ways to test insulation using ELF and ultrasound but the equipment is very expensive.
 
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