# Surge Protector Questions

How important are the plug-in retail-store-bought surge protectors for protection of household appliances? Is the danger primarily from lightning strikes and that sort of thing, or will normal fluctuations in the regional and local electrical grid produce surges? If it's a normal thing to expect from the grid, will the cheapest surge protector I can find be effective for that level of risk - do I just need the more expensive ones for protection from lightning and other unusual Acts of God? And if you've got a schpiel on surge protectors, sit down, pour yourself a martini and reel it off! (or link to it.)

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NoTime
Homework Helper
They primarily protect from lightning strikes with the active device in the unit called a MOV.
If a voltage spike (say over 300v for a US 120v circuit) the MOV switches on and shorts to ground until the voltage is once again below the switch point.
Clamping the voltage protects the rectifier diodes in your equipment from having their ratings exceeded which causes them to fail.

Most plug in electronic devices have built in surge protection nowadays.

The common wall wart is fairly immune to the lightning strike effect due to the transformer in it.

Some units also add a line filter which can reduce interference for TVs and Radios.
Generally this addition is meaningless for something like a computer.

For a direct lighting strike things are going to melt, surge suppressor or no.

My personal opinion is that anything from Monster is way overpriced BS.

http://en.wikipedia.org/wiki/Surge_protector

chroot
Staff Emeritus
Gold Member
The cheapest surge protector is probably electrically identical to much more expensive ones. They all use $2 MOVs. You might find the more expensive ones to have better workmanship, higher quality outlets, that sort of thing -- but they'll all protect your equipment pretty well. Even more expensive as power conditioners, which effectively eliminate the (slight) dangers of air conditioning system surges, brownouts, etc. Most people have no legitimate need for these conditioners. - Warren mheslep Gold Member The cheapest surge protector is probably electrically identical to much more expensive ones. They all use$2 MOVs. You might find the more expensive ones to have better workmanship, higher quality outlets, that sort of thing -- but they'll all protect your equipment pretty well.
But maybe just once. I suspect the MOV's do their job for a few microseconds and then often fail open (can't confirm this). Thus the 2nd hit takes you out.

Edit: yeah ok wikip says same under Varistor hazards but then thats wikip.

chroot
Staff Emeritus
Gold Member
Yes, an MOV works only once.

- Warren

Thanks for the answers guys and mheslep for another good question. Wikipedia had some interesting information too.

Most plug in electronic devices have built in surge protection nowadays.

The common wall wart is fairly immune to the lightning strike effect due to the transformer in it.

So does this mean that, for example, my laptop while plugged in and my cell phone while charging are protected from lightning? If so, would plugging them in through a surge protector convey any additional protection, or is the only way to do better to completely unplug them? (If, for example, there's a thunder storm going on outside.)

Lost a modem during a thunderstorm once... bits were vapourised, but I managed to repair it.

That one wasn't connected via a surge protector.

Happily my satellite box was.

NoTime
Homework Helper
Yes, an MOV works only once.

- Warren

I think that depends on if its max dissipation is exceeded.

I've seen them fail both open and shorted.

NoTime
Homework Helper
Lost a modem during a thunderstorm once... bits were vapourised, but I managed to repair it.

That one wasn't connected via a surge protector.

Happily my satellite box was.

The voltage spike quite likely came in the phone line even though the phone company installs surge suppressors.
The suppressors are good enough to protect you and your phone, but a modem has a direct ground path thru the computer frame and can start acting as an unintended surge suppressor before the standard ones kick in.

In any event I lost a few older modems to this while the other electronic equipment (no surge suppressors) in the house suffered no damage.
I haven't lost a modem in a while so I suspect the newer designs started paying more attention to the problem.

NoTime
Homework Helper
Thanks for the answers guys and mheslep for another good question. Wikipedia had some interesting information too.

So does this mean that, for example, my laptop while plugged in and my cell phone while charging are protected from lightning? If so, would plugging them in through a surge protector convey any additional protection, or is the only way to do better to completely unplug them? (If, for example, there's a thunder storm going on outside.)

Laptop and cellphone wallwarts tend to be switchmode power supplies now.
Distinctly different from the common wallwart.
The power units most likely have built in MOVs.
But as has been mentioned previously surge suppressors have their limits.
Plugging them in through an external surge protector can provide additional protection.

I was looking at some expensive ones at wal-mart, and one included coaxial and ethernet protected ports. It didn't go into detail about how these are protected, I wonder if they work essentially the same as any standard surge protector. It seems I hear about lightning storms taking out modems more than any, and that's including it happening to me. It does specify that 4 of the outlets are transformer spaced...does that make it worth a toot? I think if anything the extra money should pay for the $150,000 warrenty on your property plugged in is covered even by surges due to lightning strikes. But there's probably some loophole around that... dlgoff Science Advisor Gold Member I lost a modem from lighting. The surge didn't come in on the power lines. It came in through the phone line (yes I know. I'm still on dial-up). Now when I know a good light show is coming, I just unplug the phone line and sometimes the power cord. Yup. It was the line side stuff that was damaged. It took out 3 transistors and a resistor... the modem electronics was ok... I heard the storm begin & couldn't be bothered to get out of bed to unplug the modem... Silly me. I now unplug it every time I turn the pc off. I think that depends on if its max dissipation is exceeded. I've seen them fail both open and shorted. MOVs degrade rapidly over time, hence it's recommended to change a new surge protector roughly once every two years. Degraded MOVs are dangerous as it not only provide little to no protection for your equipment, it can potential lead to fire hazards. (http://en.wikipedia.org/wiki/Metal_oxide_varistor" [Broken]) Last edited by a moderator: The cheapest surge protector is probably electrically identical to much more expensive ones. They all use$2 MOVs. You might find the more expensive ones to have better workmanship, higher quality outlets, that sort of thing -- but they'll all protect your equipment pretty well.

Even more expensive as power conditioners, which effectively eliminate the (slight) dangers of air conditioning system surges, brownouts, etc. Most people have no legitimate need for these conditioners.

- Warren

http://computer.howstuffworks.com/surge-protector5.htm" talks about the differences between the levels of protection provided by cheap versus more expensive surge protectors. There are different ratings to look out for.

More expensive ones may also include a light indicator to tell you if the surge protector is still functioning. But again if you change it regularly, you probably wouldn't need that feature. It's just handy to have it.

I see this like buying insurance.. it's how much you're willing to go for and how much you can afford. :p

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