Insulation Test Results

[AC\DC]

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.

 

[ptonsparky]

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.

 

[AC\DC]

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.

 

[ptonsparky]

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.

 

[AC\DC]

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.

 

[ptonsparky]

The old bulldogs would overheat. POS.

 

[AC\DC]

What does POS. Stand for point of service?
Sorry I’m still learning the abbreviations

 

[synchro]

What does POS. Stand for point of service?
Sorry I’m still learning the abbreviations

Piece of Shhh..
Shaving Creme https://www.youtube.com/watch?v=G8ffkDf0ol4

 

[AC\DC]

That makes more sense OK
Thanks for that song!

 

[Russs57]

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.