MAINTENANCE OF LOW-VOLTAGE CIRCUIT BREAKERS

FREQUENCY OF MAINTENANCE.-Low-voltage circuit breakers operating at 600 volts alternating current and below should be inspected and maintained very 1 to 3 years, depending on their service and operating conditions. Conditions that make frequency maintenance and inspection necessary are:

Ø     High humidity and high ambient temperature.

Ø     Dusty or dirty atmosphere

Ø     Corrosive atmosphere

Ø     Frequent switching operations

Ø     Frequent fault operations

Ø     Older equipment

A breaker should be inspected and maintained if necessary whenever it has interrupted current at or near its rated capacity.

MAINTENANCE PROCEDURES.-Manufacturer's instructions for each circuit breaker should be carefully read and followed. The following are general procedures that should be followed in the maintenance of low-voltage air circuit breakers:

Ø An initial check of the breaker should be made in the TEST position prior to withdrawing it from to enclosure.

Ø Insulating parts, including bushings, should be wiped clean of dust and smoke.

Ø The alignment and condition of the movable and stationary contacts should be checked and adjusted according to the manufacturer's instruction book.

Ø Check arc chutes and replaces any damaged parts.

Ø Inspect breaker operating mechanism for loose hardware and missing or broken cotter pins, etc. Examine cam, latch, and roller surfaces for damage or wear.

Ø Clean and relubricate operating mechanism with a light machine oil (SAE-20 or 30) for pins and bearings and with a nonhardening grease for the wearing surfaces of cams, rollers,etc.

Ø Set breaker operating mechanism adjustments as described in the  manufacturer's instruction book. If these adjustments cannot be made within the specified tolerances, it may indicate excessive wear and the need for a complete overhaul.

Ø Replace contacts if badly worn or burned and check control device for freedom of operation.

Ø Inspect wiring connections for tightness.

Ø Check after servicing circuit breaker to verify the contacts move to the fully opened and fully closed positions, that there is an absence of friction or binding, and that electrical operation is functional.