Ground resistance is the resistance seen by the grounding conductor of an electrical system. The grounding conductor is usually an eight foot long copper rod that is buried to provide a solid earth ground for the system. NEC guidelines require the ground resistance to be less than 25 Ohms. This is easily measured with a device called a ground resistance tester, or ground resistance meter.

The lower your ground resistance is, the better connection your system has to earth ground. For most people, this means less worry about stray voltage or floating voltage, among other power system concerns.

In industrial applications and among professional electrical workers, however, the ground resistance is a more serious issue. The ground system is intended to provide a safe, zero volt baseline for the electrical distribution in a building or in outside electrical equipment. If the ground resistance is low, the ground system can be counted on to remain very close to zero volts. If the ground reistance is too high, anything bonded to the ground system can potentially be elevated to hazardous voltages in the event of a ground fault or other accident.