Littelfuse Model ALT-115-S-SW Alternating Duplex Pump Relay with Switch 95-125V 8-pin Plug-inLittelfuse ALT 115 S SW Alternating Duplex Pump Relay With Switch Product Description Model ALT alternating relays are used to alternate between two loads. The ALT is commonly used in duplex pumping applications to balance the runtime of both pumps. The Model ALT S is used in single high level float applications. When the float switch opens, the alternating relay changes state forcing the other pump to run the next time the float closes Littelfuse ALT