This is an interesting, but sort of unrelated topic, on grounds. The electrical ground of electricity is all relative. We typically use earth ground as reference for our appliances and electronics.
Today, I ran an interesting service call where the user was complaining about a RTS broadcast intercom system having a hum in it after installing a new camera. He said that whenever he connected up the ground line, it would trip the circuit breaker in the power supply.
After troubleshooting the system, I figured out that he had a bad power supply. Pin 3 was supposed to have positive 24 volts , and pin 1 was supposed to be ground. I found that the pin 1 line had negative 24 volts on it, and the pin 3 line was actually ground. The voltage potiental on the intercom system was still 24 volts, so the system worked fine...until it was earth grounded with the new camera!