A primary current injection test set injects a powerful current on the primary side of protective relay equipment or current transformer to determine how the system will react to an injection of current. Circuit breakers will respond to the current injection by either tripping, ending the flow the current, or failing, and allowing the current to continue traveling into the electrical system it is intended to safeguard. A primary injection test system will record is how long the current remains live before breaking. Performing current injection testing is essential to the maintenance of electrical systems, as circuit breakers can go a long time without being activated. A failure can be catastrophic to those using the electrical power a circuit breaker protects.