scope:

NOTE:

This guide specification covers the requirements for three phase secondary unit substations for step-down operation at primary voltages of 601 volts through 38 kilovolts, and secondary voltages, of 600 volts or less.

When feasible, provide a separate liquid-filled pad-mounted transformer outside of the facility and a separately erected switchboard/switchgear assembly inside the respective facility in lieu of a secondary unit substation. For LANTNAVFACENGCOM projects, do not use secondary unit substations with secondary current greater than 5000 amperes.

For LANTNAVFACENGCOM projects, where the available fault current is less than 12,000 amperes rms symmetrical, provide pad-mounted switchgear with a fault interrupting switch-way as the transformer primary protection device in lieu of a load interrupting switch. Clearly indicate requirements for identifying signage at switch-ways and at the transformer.