What percentage of the momentary rating must the capacity of supply branch circuit conductors and the overcurrent protective device meet?

The capacity of supply branch circuit conductors and the overcurrent protective device must meet at least 50% of the momentary rating. This requirement is crucial for ensuring that the circuit can handle temporary surges of current without tripping or causing damage to the circuit components. This 50% threshold is designed to provide a balance between safety and performance, allowing for short-term overload conditions that may occur during the initial startup of equipment or due to transient loads without resulting in nuisance tripping of the circuit protection devices.

In practice, this means that when designing a system or selecting components, electricians must ensure that the selected conductors and overcurrent protection devices are capable of handling at least half of the maximum expected momentary current draw. This practice is aligned with industry standards and helps maintain the reliability and safety of electrical systems.