I mentioned the After-Christmas power outages we had. Since then, I've learned a few things.
Mainly, I've learned that nearly all my co-workers have the larger portable generators. They assert they had a local electrician involved. They 'tie in' by simply back-feeding a breaker. Their "interlock" is strictly procedural: they manually shut off the main, then flip on the breaker. They 'remember' not to run the clothes dryer or electric range while using the genny. They watch the streetlights to see if the power has been restored.
Nearly all my co-workers not using any sort of transfer switch or mechanical interlock.
