Maybe I'll show the limits of my experience, too. I have a cheap megger that I bought through ebay.
I've never used a megger on residential work. My main use is to confirm that a motor is good. Most ground faults in a motor can be read with an ohmmeter. Apparently they are a good tool for preventative maintenance, but I never get called until something has failed.
So, when the customer has a motor that they are going to install, or start, and I am asked to check it, I hit it with 500 or 1000 volts just to cover my ass.
tim
