By which of the following a bus-bar is rated?

Answer: Option D

A bus-bar is rated based on current, voltage, frequency, and short time current.

Current: The maximum amount of current the bus-bar can carry without overheating.

Voltage: The highest voltage the bus-bar can handle safely without breakdown.

Frequency: The frequency of the alternating current (AC) the bus-bar can operate with.

Short time current: The maximum short-circuit current the bus-bar can withstand for a brief period without damage.

These ratings ensure the bus-bar operates safely and efficiently within its designed parameters.