Which device is specifically designed to indicate when fault currents have passed through?

A fault indicator is a specialized device used in electrical distribution systems to detect and indicate the presence of fault currents. When a fault occurs, such as a short circuit or ground fault, the fault indicator senses the abnormal current flow and activates a visual or audible alarm. This feature helps linemen and maintenance crews to quickly identify the location of a fault on a power line or circuit, thereby streamlining the troubleshooting and repair process.

Other devices mentioned serve different purposes. For instance, an electromagnetic detector focuses on identifying electromagnetic fields and does not specifically target fault currents. A cable spear, generally used for pulling cables through conduits or ducts, does not have any electrical monitoring capabilities. An insulation tester, on the other hand, is designed to assess the integrity of insulation in electrical equipment, ensuring it is effective at preventing leakage currents, but it does not indicate faults after they have occurred. Hence, the fault indicator stands out as the primary device for signaling the passage of fault currents.