My PD5100 Automatic Transfer Switch owner's manual states:
Description of Operation
When the shore power is applied the relay is at rest and power is transferred to the panel.
When Generator power is applied there is a 20-45 second delay and then the relay activates transferring Generator power
to the panel.
If shore power returns while the Gen power is present nothing will happen. When the Gen power is removed the relay will
drop out and allow the shore side to supply power.
Generator overrides shore power.
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