The S-240P is designed to be used with the S-4000S or S-4000H units that are part of an RSS S-4000 Modular Digital Snake. When properly connected, the S-240P will supply power to, and allow the continued operation of, the S-4000 unit that it is connected to in case the internal power supply of the S-4000S or S-4000H is damaged and fails; or if the power switch on the unit is accidentally turned off. In these rare and unexpected cases, the S-240P will allow the S-4000 unit to keep working and the audio of the system will continue without interruption. For this reason, we suggest that, whenever possible, the S-240P should be plugged into a circuit that is separate from the circuit supplying the power to the S-4000S or S-4000H.