When the EMT is used as the equipment grounding conductor (EGC) for a circuit, what is the effect on the opening time of the circuit breaker protecting the circuit?

Using electrical metallic tubing (EMT) as the equipment grounding conductor (EGC) does not affect the opening time of the circuit breaker, regardless of the length of the EMT. The primary role of the EGC is to provide a low-resistance path for fault currents, allowing the circuit breaker to detect overloads or ground faults quickly.

In a well-designed electrical system, the circuit breaker will respond based on the current flowing through the load and the fault conditions, not the length of the EMT itself. While longer lengths of conductors can introduce more resistance, the EMT is typically designed to be robust enough to minimize any significant increase in resistance that would impact the circuit's fault current path. The sense of urgency for the breaker to open relies on the current through the load and the conditions triggering the fault rather than the physical dimensions of the grounding path. Thus, the EMT effectively fulfills its function without influencing the breaker’s opening speed due to its length.