Recreational Vehicle (RV) Technician Practice Test

In order to measure the current drawn by a motor with a clamp on ammeter, where should the sensor clamp be placed?

1. Red wire

2. Green wire

3. Black wire

4. Blue wire

The correct answer is: Black wire

To accurately measure the current drawn by a motor using a clamp-on ammeter, the sensor clamp must be placed around a single conductor that carries the current. In most electrical systems, including those for RV motors, the black wire is typically associated with the negative or ground side of a circuit, particularly in DC systems. However, the key factor is that the sensor must measure current in one of the conductors while not including both the positive and negative conductors simultaneously, as this would result in a net current reading of zero. The clamp should be placed around the black wire since it completes the circuit and allows the ammeter to measure the flow of current accurately going through the motor. This method ensures that the reading reflects only the current being utilized by the motor, providing the necessary data for diagnosis or performance evaluation. The other wires mentioned do not fulfill the requirement of being a single current-carrying conductor necessary for this measurement task.