Automatic transfer switch (ATS) annual maintenance checklist

Outage or bypass-isolation plan agreed for the switch's loads

Owner agrees when loads drop or ride on the bypass, how long the switch is out of service, and how life-safety loads are covered under their procedure.

Generator service booked for the transfer and the outage

Generator service on site for the on-load transfer and to hold the set out of auto during the outage, with engine-side work left to them.

Full on-load transfer to the alternate source and back

Actual building load transferred to the generator, run under load, then retransferred, transition timing observed against the settings.

Voltage sensing checked against a calibrated meter

Controller readings on both sources compared with a calibrated meter under the energized-work procedure, pickup and dropout confirmed to the setup sheet.

Line and load connections scanned for heat under load

Terminations checked with a thermal camera or infrared spot while loaded, any hot lug compared against its neighbors and flagged.

Both sources locked out and verified dead at the switch

Normal and emergency feeds opened and locked, or the switch drawn out of its bypass-isolation frame per the manufacturer, and the parts to be worked on tested dead.

Terminations re-torqued de-energized after the scan

Switch locked out after the load test, lugs torque-verified or resistance-measured, re-torqued only where found loose, heat-discolored hardware replaced.

Main contacts and mechanism inspected

Contacts checked for pitting and burning where accessible, mechanism and arc structures inspected, lubrication per the manufacturer.

Controller battery and control power verified

Controller battery or control-power source tested, so the switch can still run its logic during an actual outage.

Insulation resistance recorded pole to pole and across open contacts

Readings taken with the switch dead and the controller isolated as the manufacturer directs, recorded and compared with last year's results.

Mechanism operated by hand through both positions

With the switch dead, the manual operator moves it smoothly to each source, it latches fully, and the auxiliary position contacts change state.

Barriers and covers back on before either source is restored

Tools cleared, barriers and covers refitted, and each lock and tag removed by the person who hung it before normal or emergency power returns.

Switch re-energized on normal and left in automatic

Normal source restored under the outage plan, switch on normal, controller in automatic with no alarms, and the exercise schedule still set.

Owner and generator service told, and the service report filed

Owner told the switch is back in automatic, generator service released to return their set to auto, and readings, test results and deferred work filed.