The automatic transfer switch shall monitor the utility power source, signal the engine/generator set start-up, automatically transfer power, and return the load to the utility source once the utility power returns and is stabilized.

Voltage monitoring shall be done on all phases on each power source. Adjustable solid state time delays shall be provided for engine start (zero to five minutes), transfer (zero to 120 seconds), retransfer (zero to 30 minutes), and for cool-down and stop (zero to 10 minutes). Other accessories shall include status indicating lights, auxiliary contacts, and a Hand-Off-Test-Auto selector switch. An automatic exerciser is not required.

The automatic transfer switch shall be of a type that allows a short time delay while transferring the load from the generator to the utility power source, to allow induced voltages to decay, and to allow transfer without synchronizing the two sources.

Acceptable manufacturers: Onan, Russelectric. (Design Guideline DG-08 § 18.2.5, dated August 2006)