Check Sockets for Improper Wiring and Faulty Ground!
Electric sockets can be bad for a number of reasons: a wire can short or fray, a wire can become disconnected, or corrode at the contact, or the wires can be connected to the wrong contact altogether! These problems can be a fire hazard, a shock hazard, a problem for polarized appliances, and definitely a problem if you are using the socket’s ground connection to Earth your shielding.
There is no need to guess because it is so easy to test for proper wiring at a socket. Simply plug in the tester and look at the result. Large LCD display indicates if ground is missing or faulty. Easy to see LEDs light up to indicate all these possible problems: