The Model ALT-X
has an internal cross-connected relay and is used in dual high-level float applications. These floats are commonly referred to as lead and lag floats.
The pumps alternate as in the ALT-S version but the cross-connected relay configuration allows both pumps to run simultaneously when both the lead and lag floats are closed.  These relays are also available with a built-in switch (SW option) that is used to manually force one of the pumps to run every time the float switch is closed. This is helpful when a pump has been removed for repair or for test purposes.  In the case of the Model ALT-X-SW, the switch essentially forces one pump to be the lead pump, while still allowing the second to run when both floats are closed.  All Model ALT relays have a built-in debounce feature that prevents the relay from  changing state if the switch or float contact bounces momentarily.