Grounding outside

Inside building there are situations where you can see 60-115 V AC between different equipment grounding points. When going outside the building the voltage differences can between different grounding points can become larger. In electrical engineering, Earth Potential Rise (EPR) also called Ground Potential Rise (GPR) occurs when a large current flows to earth through

Lack of safety ground

Besides short circuit surge currents flowing on safety ground wire there are also other situations where you can see 60-115 V AC between the equipment cases. In the age of switch mode power supplies the safety ground has a new job, ie EMC line filter ground. When the power supply EMC filter is not connected

Safety ground is not reliable ground reference

I have written quite a bot of material on Ground loop problems and how to get rid of them. The ground loop related problems are often caused by small ground potential differences between different electrical outlets. Typically those ground potential differences are few volts or less. Not your fault article by Howard Johnson published in