I put this on the outside switch. It looks like a rock to scare away bears - I don't actually know if it protects my AC from power surges, but it looks reliable, my AC hasn't failed yet and it has a bright green LED which looks reassuring. The LED is quite bright and lights up like a beacon at night. There are only 3 wires to connect, so it's difficult to screw something up. Just turn off the power first - that's why I installed it in the breaker rather than on the main panel where it could theoretically work better. You can completely turn off the power by shutting down, you can't turn off the power of the panel.
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