The SB3a Smart Booster adds expanded and updated features to a Power Cab DCC system. The first and most noticeable feature is additional power (5 Amps) to run trains and accessories.Power Cab(s) used with the SB3a can now be unplugged and used in true walk around fashion. It no longer needs to remain connected for the system to work.Up to 4 cabs can be used with the SB3a (Cab address range 2 through 5) Cabs have up to six recalls each when used with the SB3a.Additional 5 Amp boosters (DB3a) may be added to the SB3a for even more power handling on larger layouts. This manual covers only the addition and installation of the SB3a to a Power Cab system. For operation consult your Power Cab manual. The SB3a does NOT have a programming track output. The basic Power Cab provides this capability.