Alternating Relay: An alternating relay is advantageous when equal pump run-time is required. When the leading pump shuts off the next one in line will start the next time that pumping is required.

PLC (Programmable Logic Controller): A PLC controller is more advantageous when equal pump run-time or multiple pumps may need to run at the same time. An alternating relay only switches to the next pump when the one prior to it shuts off. If the leading pump may be on for extended periods of time, a truly equal run-time may not be achieved. The PLC can be programmed to allow the pumps to run for set time periods or even delay switching if conditions warrant. The PLC can also be used to log run-times as well as total hours saving the additional cost of run-time meters or dataloggers.