Section 39.153. Required placement of switches

(a) Suitable switches or cut-outs which may be manually operated shall be inserted in all leads, except a grounded conductor, to generators, motors, transformers, other than instrument transformers, and outgoing supply circuits.

(b) In most cases the switch called for should be capable of opening the circuit under overloads. In some cases as between generators and transformers banks used with them, only disconnectors shall be required.

(c) If two or more pieces of electrical supply equipment or supply lines are operated as a single unit no switch is necessarily required between them.

(d) Switches are not required in underground manholes or in transformer vaults except as may be deemed necessary by the utility to meet operating requirements.