§ 2735. Overcurrent Protection.

(a) Feeders and branch circuit conductors shall have overcurrent protection in each ungrounded conductor located at the point where the conductor receives its supply or at a location in the circuit determined under engineering supervision.

(1) Circuit breakers used for overcurrent protection of three-phase circuits shall have a minimum of three overcurrent relays operated from three current transformers. On three-phase, three-wire circuits, an overcurrent relay in the residual circuit of the current transformers may replace one of the phase relays. An overcurrent relay, operated from a current transformer that links all phases of a three-phase, three-wire circuit, may replace the residual relay and one of the phase-conductor current transformers. Where the neutral is not grounded on the load side of the circuit, the current transformer may link all three phase conductors and the grounded circuit conductor (neutral); and

(2) If fuses are used for overcurrent protection, a fuse shall be connected in series with each ungrounded conductor;

(3) Each protective device shall be capable of detecting and interrupting all values of current that can occur at its location in excess of its trip setting or melting point.

(4) The operating time of the protective device, the available short-circuit current, and the conductor used shall be coordinated to prevent damaging or dangerous temperatures in conductors or conductor insulation under short-circuit conditions; and

(5) The nominal rating of the cables will be as required by Section 2821.

(b) The following additional requirements apply to feeders only:

(1) The continuous ampere rating of a fuse shall not exceed three times the ampacity of the conductors. The long-time trip element setting of a breaker or the minimum trip setting of an electronically actuated fuse shall not exceed six times the ampacity of the conductor.

Exception for fire pumps: Conductors may be protected for short circuit only.

(2) Taps to a feeder need not have separate fault protective devices, provided that the conductors are capable of withstanding the maximum short circuit current that can occur for the time necessary for a fault protective device on the source side of the conductors to operate.

HISTORY

1. Editorial correction filed 11-2-83 (Register 83, No. 45).

2. Amendment of section and Note filed 4-1-2009; operative 4-1-2009. Submitted to OAL for printing only pursuant to Labor Code section 142.3 (Register 2009, No. 14).

Note

Note: Authority cited: Section 142.3, Labor Code. Reference: Section 142.3, Labor Code.