Perko Medium Duty Battery Selector Switch w/Alternator Field Disconnect & Key Lock. Capacity 250 Amps continuous 360 Amps intermittent. When used with non-unitized alternators these models will interrupt the field current (reducing the possibility of damage) if turned "OFF" with the engine running. 5-1/4" Diameter. 2-5/8" depth. Specifications for Perko 8504DP Medium Duty Battery Selector Switch w/Alternator Field Disconnect & Key Lock: Manufacturer: Perko Color: Black Amperage: 250 amps Features of Perko 8504DP Medium Duty Battery Selector Switch w/Alternator Field Disconnect & Key Lock AFD: Yes Lockable: Yes Positions: 2 Continuous Amperage: 250 Package Contents: Perko 8504DP Medium Duty Battery Selector Switch w/Alternator Field Disconnect & Key Lock Perko 8504DP: Medium Duty Battery Selector Switch w/Alternator Field Disconnect & Key Lock 8504DP