Asbestos-cement arc-chamber barrier plates and interphase barriers used inside Federal Pacific Stab-Lok circuit breakers and panelboards

Product Description

Federal Pacific Electric’s Stab-Lok circuit breaker product line — described more fully on the Stab-Lok panels page — depended on an internal arc-suppression assembly to safely interrupt fault current. Behind and around the arc chute, the breaker required rigid dielectric structure — walls, back-plates, and interphase barriers — capable of withstanding the ionized gas, heat, and mechanical shock generated during an arc-interruption event.

Plaintiffs alleged in publicly filed U.S. asbestos litigation that Federal Pacific specified asbestos-cement composition for these barrier and back-plate components — a hard, cementitious material bound with chrysotile fiber that offered high dielectric strength, structural rigidity, and heat resistance at low cost. Asbestos-cement barriers were common in mid-century circuit-breaker design because they held their shape and dielectric integrity under conditions that would char, deform, or fracture unreinforced phenolic or thermoplastic material.

The asbestos-cement barrier and back-plate components worked in parallel with the asbestos arc-chute material identified in the Stab-Lok arc-chute product page — two distinct asbestos-containing components inside the same breaker.

Workers Exposed

Asbestos-cement is a friable material when disturbed. Plaintiffs alleged three principal exposure pathways for the Federal Pacific arc-chamber barrier plates:

Breaker disassembly during service. Maintenance electricians who opened Stab-Lok breakers for internal service — testing calibration, replacing burned contacts, cleaning arc-damaged interiors — chipped and scraped the interior barrier surfaces, releasing cement dust.

Arc-damaged breakers. A Stab-Lok breaker that had experienced a heavy fault-interruption event or partial failure often showed cracked, spalled, or partially disintegrated barrier plates. Workers pulling the damaged breaker for replacement encountered friable material that had already been mechanically degraded by the fault.

Destructive panel removal during renovation and demolition. Construction electricians and demolition workers who tore Stab-Lok panels out of walls during residential renovation, commercial fit-out, or industrial demolition frequently broke the panel bodies and internal breakers in the process. Fractured asbestos-cement barrier debris entered the workplace atmosphere as the panels were reduced for disposal.

Plaintiffs alleged that this work was performed without respiratory protection and without warning labels identifying the internal barrier material as asbestos-cement.