The Triplett EG480 can measure 2- and 3-wire Earth Ground Resistance (in 3 ranges) and Earth Voltage (200V), plus multimeter functions AC/DC Voltage and Resistance (2000 Ohms). An earth ground is used as a zero-volt reference point for power substations, buildings, communication towers, and as a path to dissipate lightning strikes to prevent damage to them. The NEC (National Electrical Code) requires that a single path to ground should be 25 ohms or less. If it is higher than 25 ohms, you should add an additional ground rod 6 feet away. The Triplett Earth Ground Resistance Tester provides an easy way to check this reading in installed systems or for a good location to install a new system. Additional features include dual LCD display with backlight, Data Hold function, auto power off, and a low battery indicator. CAT III 1000V safety category. Includes test leads, (2) auxiliary earth rods, (6) AA batteries, and carrying case.