Which clearing time will be fastest on a molded case circuit breaker equipped with an electronic trip unit?

The fastest clearing time on a molded case circuit breaker equipped with an electronic trip unit is achieved with instantaneous pickup. This setting is designed to respond and trip almost immediately when a fault condition occurs, thereby minimizing the duration of fault current and reducing the potential for damage to the electrical system or connected equipment.

Instantaneous trip settings are particularly important in critical applications where rapid disconnection from potentially hazardous conditions is essential for safety. This type of trip eliminates delays associated with other settings that may require a certain period to assess the fault condition before responding. Thus, it provides immediate protection against short circuits at high fault currents, ensuring that any electrical faults are cleared as quickly as possible.

In contrast, the other options involve various forms of time delays or adjustable trip characteristics that permit a brief period of current flow, which can be useful in certain scenarios but do not offer the same level of rapid response as instantaneous pickup. These settings are typically intended for overload or temporary inrush conditions rather than urgent fault clearing.