Insulation Test Results

Status
Not open for further replies.
A

AC\DC

Senior Member
Location
Florence,Oregon,Lane
Occupation
EC
Hello, I recently Purchased a Fluke 1587FC for a job I posted on this site. Next day I got a call for a blown fuse on L2 in the service disconnect. I don't believe it was overloaded since it serves only lights, and L1 only reads 40 amps on a 100 amp fuse.

The equipment and wire are about 75 years old. Wires are ran in RMC, 3 wire circuit, RMC is EGC

I disconnect all wires to test them

I did a spot test at multiple ranges ohm range from L2-G. Was fine till I got to 500v and 1000v. So I did a DAR test( the 30/60) and on L2 to ground. I got 328m to 585m. Dividing them gave me 1.1 so that wire looks like it's on its last leg (To me)

L1 to ground was 2.2g
L1 to N was 2.2g
Neutral to ground was 1.1g to 2g
L2 to L1 was 1.9g to 2g
L2-N was 1.5g to 2g

So looks like its Going to the RMC

I took a few classes on flux for insulating testing. So I feel I am correct. I would just like your guys input, since this is my First Insulation test by my self.
 
Last edited:
I would look closer at the connections for L2. Any discoloring? Use a thermal camera or do a FOP, voltage drop, across the connections. The VD drop across the connections should all be similar. You will need a meter that reads in the mVolts.

Did you remove the wires tested from the connections on both ends? Wires clean and dry at both ends?
eta:
I see you removed them...

Looked up your new toy. Nice.

You could try the resistance readings across those connections as well, if you prefer not to work hot.
 
I’m getting the fuses today.I’ll see if Any in my meter do millivolts. I didn’t do the resistance and they’re all close. I was thinking it shorted out because of the insulation test and also the fuses blown apart.
 
Details...the fuse blew apart? What is your voltage?
Post a picture of your disconnect.

I would not consider any wire that tests in the G ohm range as bad on the first tests of it. You would need a trend line developed over time.

That does not mean you did not have a fault that has now blown apart or is clear.
 
240 V single phase. The disconnect an old bulldog three fuse disconnect. I agree any wire in the gig ohms are good. Line 2 to ground was at the 328 mega ohms to 500 Mega ohms. on my dar test.Thats the one that’s bad and blew the fuse.
 
Don't forget to meg the disconnect. People always think it has to be the wire or the load. Can't tell you how many times I have discovered carbon arcing on fuse holders, motor starters, etc.
 
Status
Not open for further replies.
Top