Auxiliary Supply Panel (HB1, HB2) consist of completely wired contactors, circuit breaker etc. it controls the input to several Auxiliary Assemblies of Locomotive like Machine Room Blower, Compressor, Crew Fan, Cab Heater etc.
Control Panel (SB1, SB2) used to control the various function of Locomotive. Control panel provide interface to locomotive device like Pantograph, Traction Converter, Auxiliary Converter, Pneumatic Panel as well as to the control electronics.
Filter Cubicle (FB) is a panel with surge arrester, current sensor, contractor, capacitor etc. It control filterning high frequency harmonics induced from the primary of the main transformer.