Theory Of Operation

VOLTAGE DROP TESTING:  Voltage drop is the reduction in voltage in an electrical circuit between the voltage source and load components. A voltage drop test is an effective way to locate excessive resistance in a typical series circuit. The wires and connectors of a circuit should contain almost no resistance and all  the voltage should be consumed through the load. A circuit must be complete and energized in order to perform a proper voltage drop test of the circuit, meaning that there must be a source voltage (usually 12 volts), some type of a load with resistance, and a path to ground. The "load" is the component using the power, such as a light, starter, or blower motor. If a circuit has excessive resistance, it prevents the wire from carrying sufficient current under high load conditions. The acceptable amount of voltage drop across a circuit is dependent upon the resistance of the component in the circuit that is being tested. For example, a 12 volt supply circuit that has 2.0 Ohms of resistance will have a greater voltage drop measurement when connected to a component with 6.0 Ohms of resistance than it will if connected to a component that has 60.0 Ohms.

• A 12 volt supply circuit with 2.0 Ohms of resistance, connected to a component with 6.0 Ohms, would have a voltage drop of 3.0 volts.
• A 12 volt supply circuit with 2.0 Ohms of resistance, connected to a component with 60.0 Ohms would have a voltage drop of 0.3 volts.