Ground Bond Tester

A ground bond tester is specifically designed to verify the integrity of the protective earth grounding system of the device under test. The ground bond test is done by passing a high current (normally in the range of 25 to 40 amps) from an exposed conductive point on the chassis to the earth ground point.

Typically, a maximum resistance permittedfor a ground bond tester is 0.1 ohms. The theory behind a ground bond test is quite simple. If a unit develops an insulation failure, then the line voltage could come in contact with the conductive chassis. If the chassis was not grounded, then it would be setting there at line voltage and presenting a serious electrocution hazard to anyone coming in contact with the device. Protective earth grounding of a conductive chassis minimizes the risk that the chassis can be setting at an elevated voltage. However, the grounding system must be robust enough to survive the flow of electrical current until the protective circuit breaker kicks open. Imagine the following scenario without a ground bond tester, where an insulation breakdown occurs.

The process of the ground bond tester is when the chassis is electrified, current begins to flow from the chassis through its grounding wire to the earth ground point. The grounding wire has several broken strands and cannot handle the flow of current, so it fuses open before the breaker can kick. Now the chassis of the device is setting there at line voltage and presenting a serious electrocution hazard to anyone coming in contact with it, thus the need for the ground bond tester. In order for a protective grounding system to work properly, it must be tested by a ground bond tester to see if it is able to handle greater current levels than the typical circuit breaker. High current devices may call for a ground bond test using a current that is 50 to 100% higher than maximum load current of the device.