The interlock that is sold on the internet is listed by Wyle labs, another NRTL.
I have been in a discussion with an inspector about these interlocks on another BB and he is saying there is no legal way to connect a portable generator to a house anyway.
Also your typical Briggs generator is not listed at all.
OTOH this inspector has no problem converting well pumps and furnace blowers to cord and plug "in an emergency" citing 590.
