Monitoring the Integrity of Engine Start Signal Circuits


The 2017 edition of the National Electrical Code® (NEC®) introduced a requirement to continually monitor the integrity of generator start signal circuits. This paper explains how unmonitored wiring presents a reliability risk, and describes the responding NEC requirement. It also describes ASCO’s solution for complying with the code, without having to rewire existing power equipment control circuits.


In order to provide an engine start signal to an emergency generator, a transfer switch typically uses a circuit controlled by a normally closed contact. During normal operation, this component is energized and the contact remains open, but closes when the Automatic Transfer Switch (ATS) requires generator power. Upon closure, the contact completes the circuit used to send a start signal to the engine of a standby generator. The engine start signal wiring is shown in Figure 1.