Megohmeter usage tips

[Ravenvalor]

Hello Friends,

I am using a megohmeter for the first time. I am using it to check the insulation on all of the conductors in a home. The reason that I am doing this is because the local power company's primary line (13,000 volts) fell into a customer's front yard, energized the CATV cable going into the home and fried most of the electronics. Does anyone have any operation tips that they would not mind sharing with me?
The megohmeter is a Fluke 1520.

Thanks

 

[zog]

Been covered many, many times here, just search the forum for megger.

 

[Ravenvalor]

Been covered many, many times here, just search the forum for megger.

10 4

Thanks.

 

[Ravenvalor]

Megging a home right now. Can someone please PM me. Thank you.

 

[Ravenvalor]

Thanks volta for the timely advice.
I had everything sensitive to high voltage disconnected from the electrical system before I started.
I then proceeded to megg all of the circuit conductors in the electrical panel.
I tagged every circuit with a label stating the HN, HG, NG readings.
There were some circuits that were reading infinity, some were in the 500M range some in the 300M range and then about 4 - that were under 50M. I immediately started on one in the 30M range. After about an hour of narrowing down I found a receptacle in the bathroom that was reading 30M. I replaced the receptacle and now that circuit is in the 600M range. I did not get to narrow any more problems down due to the time constraints.
I was wondering which ranges should I be concerned about and which ranges are fine?

Thanks for all of the help.

 

[kbsparky]

Did you megger a circuit with a GFI receptacle in it?

We recently megg'd out a whole house after a lightning strike. There were a couple of circuits that I could not get a satisfactory reading on. Here are a few items that had to be located and disconnected before the megger would read properly:

• Paddle fan remote receivers
• Photocell in post lamp
• garage door opener
• gas fireplace remote control unit
• GFCI outlets
• door chime transformer

 

[Ravenvalor]

Is 100 Megohm's acceptable?

Is 100 Megohm's acceptable?

Thank you.

 

[Volta]

Thank you.

I would consider it to be the lowest end of acceptable.

Comparison is key, as we can't look at previous records for a particular cable here, noting the differences from cable to cable and looking closely at the outlying readings may do some good.

And to be anal about it, I wouldn't call your best readings infinity, rather I'd think of them as "over one billion', or wherever the scale tops off. In this case the cables won't likely be megged again, but if they are with say, a 2 gig scale, and the reading is 1.5 gig, the next tester won't have to wonder if the resistance has dropped.

 

[Ravenvalor]

Great advice Volta, it helped me to see the issue much clearer.

Thank you,

 

[Volta]

Great advice Volta, it helped me to see the issue much clearer.

Thank you,

Your welcome, glad to help!