The Maxiswitch 4-Way is a control unit used for safely switching HID lights on and off.
Segmental timers alone will not handle the electrical load demanded by HID lights - it works by diverting the live load around the segmental timer to a contactor/relay and the timer simply switches the contactor/relay to complete/break the circuit.
A core component of any grow room and rated 13A, it can handle up to 4 x 600W grow lamps (3A each). There's two plugs running from it - one goes into the mains socket and the other goes into the timer.