The GE FK and FKD are oil circuit breaker contact assemblies used in GE-manufactured oil circuit breakers. Unlike the LTC articles in this series, the FK and FKD are circuit breaker contacts, not load tap changer components. The FK is used in FK-series GE OCBs and comes in several variants based on the breaker rating. The FKD is a separate design that uses a yoke-based contact assembly with finger contacts and an arcing contact plate. Both designs include a baffle stack assembly that is a critical wear item and must be inspected and replaced on the same schedule as the contacts themselves.
The FK series spans several breaker ratings and contact configurations. The three primary variants are the FK-15-5-72-5, the FK-69-2500, and the FK-339. Each is dimensioned for its specific breaker rating and the contact assemblies are not interchangeable between variants. Before ordering replacement contacts, identify the breaker model and rating from the breaker nameplate and match it to the correct FK variant.
The FK-339 has an additional complication: it uses two intermediate contact styles, designated Style A and Style B, which differ in the contact geometry at the intermediate contact surface. The intermediate contact is the contact element that bridges between the arcing contact and the main contact during the opening and closing sequence. Inspect the existing intermediate contacts before disassembly to determine which style is installed — Style A and Style B are not interchangeable, and an incorrect intermediate contact will not produce the correct opening and closing sequence timing that the breaker is designed for.
FK contacts carry the arcing duty on each interruption. Inspect the contact tips for erosion depth and compare to the manufacturer’s minimum specification. Contacts that have worn past the minimum tip dimension must be replaced before the breaker is returned to service. OCB contacts that operate beyond their wear limit shift interruption energy to the underlying contact body, which can produce failures that damage the contact mounting structure in addition to the contact itself. At higher interruption duties, contact wear accumulates faster — breakers that protect high-fault-current feeders or that have operated on fault current should have contacts inspected immediately after any fault interruption, not just at scheduled intervals.
Measure contact resistance across the closed breaker contacts at each maintenance interval. Compare to the baseline and to the manufacturer’s maximum allowable contact resistance. An elevated contact resistance reading on a serviceable-looking contact indicates surface oxidation or poor contact pressure — clean the contact surfaces and recheck. A resistance reading that remains elevated after cleaning indicates a contact that has lost its seating force or developed subsurface damage and must be replaced.
The FKD uses a yoke assembly that carries a set of contact fingers and an arcing contact plate. The yoke assembly is the structural and electrical backbone of the FKD contact group — fingers mount to the yoke and make contact with the mating stationary contacts during the closed position, while the arcing contact plate handles interruption duty during the opening sequence. Inspect the yoke for physical integrity, cracks at the finger mounting points, and any evidence of deformation from contact forces or thermal stress. A yoke that has cracked at a finger mounting point will allow that finger to shift under operating loads, changing the contact geometry and producing uneven current distribution across the finger set.
The arcing contact plate on the FKD absorbs arc energy during interruption. Inspect the arcing contact plate for erosion at the arc impingement zone and compare remaining material to the manufacturer’s minimum specification. A deeply eroded arcing contact plate that allows arc energy to reach the yoke surface will cause yoke damage that requires replacement of the entire yoke assembly rather than just the arcing contact plate.
The baffle stack assembly is mounted in the arc quenching path and is responsible for deionizing and extinguishing the arc that forms during contact separation. It is a critical wear item on both FK and FKD breakers — a baffle stack that has eroded, cracked, or carbonized to the point of reduced quenching effectiveness increases arc duration on each interruption, which accelerates contact wear and can result in a failure to interrupt on a high-current fault. Inspect the baffle stack at every contact maintenance interval. Replace baffle stacks that show extensive carbonization, structural cracking, or measured erosion at the arc channel surfaces. Do not return a breaker to service with an out-of-specification baffle stack even if the contacts themselves are within wear limits.
GE OCB maintenance intervals are interruption-count based, with separate thresholds for fault interruptions vs. normal switching operations. A single fault interruption produces far more contact wear than a normal switching operation. Maintain a log of all fault operations and initiate contact inspection after any fault interruption at or above the breaker’s rated fault interrupting current. UnderNERC PRC-005, circuit breakers must be maintained on defined maintenance intervals with documented results. Contact resistance testing, insulation resistance testing, and trip timing tests are part of the standard NERC maintenance record for OCBs.
Southern Switch stocks FK and FKD contact assemblies including FK-339 Style A and Style B intermediate contacts and the FKD yoke assembly. Confirm the breaker model and rating from your nameplate before ordering.