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Q: How do surge protectors work?

Physicist: To control power in a house or an outlet you’d generally use a fuse. But fuses are slow, they need time to heat up. A surge (or the faster “spike”) happen too fast, so reacting to a surge is no good. Dealing with a surge properly has to be built into the nature of the machine. There are two (general) ways to do this: “choking” and “shunting”.

Shunting is what a sink does when it over-flows. You never worry about water getting to the ceiling above your sink, because the moment the water gets as high as the edge the sink starts overflowing and stops filling up. The ceiling is protected by the innate nature of the sink (which doesn’t need to react, it just “does”).

The zero-finesse surge protector is just a varistor placed between the power line and the ground line. The ground line (in this metaphor) is the floor around the sink, where all the overflowing water gets dumped.

While there is some fancy quantum mechanics tied up in varistors (I’m talkin’ valence and conduction bands here), what really gets my physics juices jumping is waves and frequencies.

The other type of surge protector is essentially a “band pass filter” centered around 60 hz (the frequency of the current in the electrical grid). You can think of this as the “radio” of the surge protector tuning into the “station” of the wall outlet (and tuning out everything else).

Now, I hope this doesn’t come as a shock to anyone, but most surges (e.g., lightning strikes) are fast. It turns out that because of the Uncertainty Principle, things that happen really fast are necessarily spread out over a lot of frequencies (small time uncertainty means large frequency uncertainty).

So while a power surge may have a lot of energy overall, the amount of energy right around 60 Hz, where it can get into the circuit, should be fairly small. You can build chokes to limit the frequencies that get past the surge protector by using carefully tuned LRC circuits, but generally (since most of the energy is in frequencies much higher than 60 Hz) you can just build a “low pass filter”.

Which is just fancy talk for “an inductor”.

Which is just fancy talk for “a coil of wire“.

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