Through an interlock kit or a transfer switch, full stop. Both connect the generator to chosen circuits through the panel and mechanically prevent power from ever flowing backward onto the street, where it can injure or kill a line worker restoring your neighborhood. Published guides put the hookup at $500 to $1,500 installed depending on method and distance. The two fatal shortcuts are the dryer outlet backfeed cord and running the generator in a garage; outage season produces carbon monoxide deaths every year from the second one alone. Generator outside, 20 feet from windows, feeding an inlet: that is the whole safe pattern.
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