ATC Diversified Electronics duplexor alternating relay ARA & ARB series can be specified in control panels where two loads alternate equal run times on the loads. The control switch initiates the alternating action and LED indicators display the position of the output relay. The ARA & ARB series both provide an automatic alternating sequence. The ARB series comes with a three position switch which allows field selection of duplexing action, or locking in the A-B or B-A sequence.