I recently had a power surge at my house, and some devices on my surge protectors died (graphics card, tv, modem) but others were fine (router, xbox, apple tv). I don’t understand what the difference was, can surge protectors be explained more on how they work?
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From an electrical perspective, any time you have two devices in parallel they will have an equal potential (voltage) across them. So if you have a printer, PC and LED light all plugged into a power strip (i.e., in parallel), they all have the same voltage 120v across them.
But if a jumper is placed in the last slot of the power strip, you have a direct short also in parallel. If the jumper is zero impedance, then by Ohms Law, there will be no voltage drop across it. So by Ohms Law, the other devices in parallel (the printer, PC, LED) will also have zero voltage across them. The jumper has effectively collapsed the voltage across your devices and source voltage is dropped internally in the source itself and the accompanying wires. Kirchoffs 2nd Law.
An arrester is basically a jumper that is voltage activated. It sits in parallel with your devices and appears electrically as an open (high impedance) circuit under normal voltage conditions. But they have a voltage threshold (often around 330 volts) where the impedance collapses and they become a short instead of an open. That in turn collapses the voltage across across any device in parallel with it. When the high voltage is removed, the arrester becomes a high impedance device again and the circuit is back to normal.
That’s the theory.
In reality, the arrester (normally a metal oxide varistor (MOV) or something similar) doesn’t go to zero impedance, so there is always some voltage drop still present. Also, the arrester has to have the capacity to survive being a short circuit for the brief length of time it is acting as such. This capacity is expressed in either amps, Joules, or both.
So in answer to your question, the voltage across all the devices is mitigated to some extent, but not entirely, and at that point whether they survive or not is more a matter of their individual protection and robustness. Having one device survive a surge while another dies is very common.
They are NOT an over voltage device; they are a surge/spike protector. In other words, a condition lasting milliseconds if not microseconds. A sustained over voltage, like from a bad transformer, will simply destroy it if it exceeds its voltage rating.
There are a multitude of sources for surges, not only lightning. Utility device operations are a constant source (breaker operations, capacitor bank switching, etc.) and while they are usually of longer duration, they are usually lower energy. Anyone thinking these are infrequent occurrences has never seen an isokeraunic map.
[https://hazards.fema.gov/nri/lightning](https://hazards.fema.gov/nri/lightning)
Bottom line. You are not aware of most surges.
An arrester is like a seat belt. A dog runs in front of your car, you hit the brakes and the shoulder strap goes tight. No blood, no foul. Then someone hits you going 30 mph in an intersection. You may have a bruise, but you didn’t lose your teeth on the steering wheel.
But if you hit a semi going 70 mph head on, you’re dead.
Arresters are the same way. If lightning hits your house, it won’t matter if you have an arrester or not. But if it hits a block away, you might be fine. And most do. And as noted, you probably aren’t even aware of most surges.
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