Final answer:
Sub mains and final sub circuits with a rating over 100 amps per phase require protection and correct design to safely handle high currents, which includes using the appropriate gauge wiring, rated devices, and adhering to electrical codes.
Step-by-step explanation:
For electrical circuit design purposes, sub mains and final sub circuits with a rating exceeding 100 amps per phase must be appropriately protected and designed to handle such high current levels. This involves selecting the correct gauge of wiring, devices such as circuit breakers or fuses rated for the higher amperage, and ensuring proper installation practices to prevent overloading and potential fire risks. It's important to follow electrical codes and standards which dictate the specific requirements for these high-capacity circuits.