Larry W4CSC wrote:

Proper transfer equipment OPENS the circuit between the time it disconnects
from one AC source and connects to the other. There are no spikes. Break
before make it's called.

You'll notice a little dark period between when the AC line disconnects and
the genset connects when the transfer switch is thrown, automatic or
manual.

Surely a double throw relay does this as well in that it cannot connect
one (inverter say) unless the other (shore power) is disconnected.
Unless there is a much bigger delay than I am thinking (i.e. 20ms).
Even then I wonder what the delay would need to be to ensure no spike?