O.T. Surge protectors losing effectiveness ?

O.T. Can surge protectors such as the kind we use on the back of the computer desk that have multiple outlets, lose the "surge protection effectiveness"? I was told this by computer techs at Best Buy and other stores. Supposedly, they will still function as electrical outlets as normal. If so, how do we know when this happens? How do we test for this?

JH

As I understand it, if an electrical surge should happen and the surge protectors do their job, their effectiveness may be reduced after the event. My guess is that specialized equipment is required to determine if they have been damaged.

Bob
WB8NQW

The answer to the first part of your question is yes, the techs didn't lie to you. As for testing I don't know but it would seem possible that testing would/could degrade the unit. There is plenty of information on Google.
Karl

Yes, surge protectors can "go bad". The device that does the protection is called an MOV and are placed across the terminals inside of a surge protector. The idea is that the MOV is designed to start conducting at a designed voltage and any voltage above the threshold is shunted to ground or across the terminals limiting the voltage. MOVs are designed to be able to absorb a specific amount of energy. If this level is exceeded, the MOV sacrifices itself while absorbing the voltage spike. The problem is that the cheaper surge protectors do not use a method of reporting the MOV condition. The better ones do.

It is usually considered best practice to replace a surge protector or at least the MOVs after a significant voltage spike.

"It depends." MOVs usually fail by shorting, permanently, according to what I recall from published information from (I think) GE. Also IIRC, this can take a few big shunts or a lot of small ones to occur. That's why all the suppressor strips (should) have (fast!) breakers or fuses. If they short for long enough before the breaker trips or the fuse blows, MOVs can catch fire or split. If they split before the breaker trips, you lose surge suppression entirely and might never know it.

We have very dirty power where I live, and used to have a lot of failures of electric and electronic equipment. I had whole-house MOVs (about the size of a brick, each) put on both legs in the breaker box when the service was redone, and also have MOVs on power strips for some sensitive radio and stereo equipment. If the breakers or fuses ever blow I'll replace them. But for at least 15 years now we have had no problems of any kind with the equipment or the MOVs. They've all eaten lots and lots of little surges by now.

As far as I know, MOVs are not designed to provide lightning protection of any sort. They're only intended to eat normal commercial power surges. If you're after lightning protection, look into PolyPhaser or similar stuff, and install it as directed. MOVs on power strips are to correctly selected and installed PolyPhaser devices what a Harbor Freight tabletop drill press is to a 30HP CNC mill. All my antenna connections run through PolyPhaser gas discharge devices that are very, very well-grounded to the ring that surrounds the house.

John

Thanks guys for the replies.

n2zon: Do the wholehouse MOV's have something like a fuse of fusible link. How do you know when they are blown?

JH

James H Clark said:

Thanks guys for the replies.

n2zon: Do the wholehouse MOV's have something like a fuse of fusible link. How do you know when they are blown?

JH

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MOVs typically fail by the "breakover" voltage decreasing as the small internal "crystals" (particles) short due to higher energy "hits". If it gets low enough, it starts to conduct during regular line current peaks, and soon fails altogether.

UL requires MOV surge protectors to have thermal and overcurrent protection*. Mostly the whole house ones have lights on each leg, AFTER the protection. So if it fails, the protection opens, and the light goes out.

The protection is sensible. I have seen MOVs that simply disappeared. Part of the case was still there, but the "works" had vanished, vaporized by the heavy current when they failed. When I say "vanished" I mean that the "works " were still present, but in the form of a dirty (and probably conductive) coating over the rest of the stuff in the unit. That's undesirable......

An MOV can handle a LOT of peak power, but not for long. It's intended to cut the peaks off short transients, Such as ones typically used in testing (and representative of reality). for instance 1.2 x 50 microsecond or 8 x 20 microsecond pulses. They are NOT intended to protect against longer overvoltages from causes like connecting to wrong voltage, faults in the power grid, etc.

* The MOV can draw a small current at full voltage, which is the usual endpoint of their life. Even though it is relatively small, it can overheat the device, which may only be the general size of a US "quarter", say 23mm or so diameter.

What he said. My big MOVs have the lights JST described and are plumbed into the system through breakers. If the lights go out or the breakers trip, it's time for new MOVs.

I think the short version is, "no, they don't become less effective." IMO, they either work (with decreasing trip voltages as they eat surges over time) or don't work (due to eventually shorting or because they've been blown completely apart). But an EE I am not, so take this with an appropriate grain of salt.

John

JST said:

MOVs typically fail by the "breakover" voltage decreasing as the small internal "crystals" (particles) short due to higher energy "hits". If it gets low enough, it starts to conduct during regular line current peaks, and soon fails altogether.

UL requires MOV surge protectors to have thermal and overcurrent protection*. Mostly the whole house ones have lights on each leg, AFTER the protection. So if it fails, the protection opens, and the light goes out.

The protection is sensible. I have seen MOVs that simply disappeared. Part of the case was still there, but the "works" had vanished, vaporized by the heavy current when they failed. When I say "vanished" I mean that the "works " were still present, but in the form of a dirty (and probably conductive) coating over the rest of the stuff in the unit. That's undesirable......

An MOV can handle a LOT of peak power, but not for long. It's intended to cut the peaks off short transients, Such as ones typically used in testing (and representative of reality). for instance 1.2 x 50 microsecond or 8 x 20 microsecond pulses. They are NOT intended to protect against longer overvoltages from causes like connecting to wrong voltage, faults in the power grid, etc.

* The MOV can draw a small current at full voltage, which is the usual endpoint of their life. Even though it is relatively small, it can overheat the device, which may only be the general size of a US "quarter", say 23mm or so diameter.

Click to expand...