What is the term for the difference in potential observed when the CP current is interrupted?

The term that describes the difference in potential observed when the cathodic protection (CP) current is interrupted is known as IR Drop. This phenomenon occurs when an electrical current passes through a resistive element, causing a voltage drop across that element due to its resistance. When the CP current is turned off or interrupted, the voltage measured will differ from when the current was flowing, as the resistance in the circuit will maintain some level of voltage drop due to the previously flowing current.

Understanding IR Drop is crucial in cathodic protection testing because it helps professionals identify the effectiveness of the CP system and determine if there are any issues that need to be addressed. The analysis of IR Drop can provide insights into the performance of the protective system and its components, ensuring that the structures remain protected from corrosion.