Check with a megger household wiring

Good afternoon, dear techies, please tell me in the next question. In one of the rooms with a central input on the machine, the shield is periodically completely knocked out, I have not been there yet, but I made assumptions that I would act already in place. I need specific advice in working with a megger, can someone tell me on the basis of experience in years and cases. I understand the cable with a good cross section to check, twist and twist, but what is the minimum indicator in ohms for home, household wiring. In Omaha, in order to understand that it still has an acceptable limit to the short circuit, or go straight to zero at all? A 500 Ohm number is spinning in my head. I have a 2500 V meger with switching limits to 1000 V, thanks in advance.