The first step is to determine how to mount the Tripp Lite PDU in a rack: either vertically or horizontally. When mounted vertically, it occupies no rack spaces (0U), because it is attached onto or behind one of a rack's vertical rails. Select PDU models feature button and tab mounting to simplify horizontal (0U) installation. The second step in the selection process is to determine the input voltage the Tripp Lite PDU will be connected to. Tripp Lite Single-Phase PDUs plug into a single-phase source and deliver single-phase power to connected devices. Tripp Lite 3-Phase PDUs allow a customer to distribute Single-Phase power from any 3-phase power source. The PDU divides the 3-phase power into three separate single-phase circuits. The National Electrical Manufacturer's Association (NEMA) has developed standards for plugs and receptacles to ensure that end users do not accidentally connect devices to power sources with incompatible voltages and amperages. If the customer decides that all they need the PDU to do is to simply distribute power to multiple devices, the Tripp Lite Basic PDU is the best solution. To locally view the PDU load (in amps) of all connected devices a Tripp Lite Metered PDU is the ideal solution. Likewise, if the customer wants to remotely view the PDU load and alarms the Tripp Lite Monitored PDU is the choice. To remotely control individual PDU outlets a Tripp Lite "Switched" PDU is ideal.