[en] On November 23, 1991, while performing an eighteen month engineered safety features operability test, the licensee for the Millstone Nuclear Power Station, Unit 3, noted that control power was interrupted to three safety-related motor operated valves (MOVs). The valves were located in the charging, component cooling water, and steam generator atmospheric dump systems. The licensee inspected the valves' control power circuitry and determined that three normally energized auxiliary relays had failed. These relays provided control power alarms and thermal overload protection for the MOVs. The relay failures rendered each valve inoperable. The relays, which had been in service for about seven years, were class J10 relays with J20M magnet block assemblies and standard G10JA126, 120V, 60 cycle coil assemblies manufactured by the ITE/Gould Manufacturing Company. Inspection of the relays revealed that the movable plastic armature carrier, which surrounds the core and coil, and the retainer for the magnet yoke assembly were discolored, brittle and severely cracked. Insulation degradation was severe, allowing electrical shorts to develop within the coils. The licensee concluded that the failures resulted from the thermal aging of the coil assemblies and plastic parts near the coil assemblies