How does surge protector/supressor work?

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Old 03-10-06, 11:38 AM
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How does surge protector/supressor work?

After a recent power surge in my house, I am considering adding surge protectors/supressors to important circuits so that I can be at least partially protected. However, I realized that I know almost nothing about how these devices work and what are the differences between surge protectors and surge supressors. So, here I am am with my questions, humbly asking the board for help...

There are home-type multi-outlet surge protectors that you plug into receptacles and then you plug your electronic devices into these protectors. (Usually can buy in any department/home/office store.) And then there are devices that are also called surge protectors/supressors but which one needs to hardwire on a circuit or install on an electric panel. What are the differences between these two types (if there are any)? And how do they work?

What are main characteristics of good surge protectors/supressors? How to distinquish a "good" one from a "bad" one? What do the ratings (joules, etc.) really mean?

What do these surge protectors/supressors protect from? (And from what they don't protect?)

As always, thanks in advance!
 
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Old 03-10-06, 12:06 PM
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It all depends on where you live, what kind of surges you typically get in your area, and how expensive the stuff you have to protect is. Most people get by with a simple $10-$20 power strip with built-in surge suppression for their computers and maybe their stereo or HDTV. The more expensive ones can absorb surges of higher energy, so look at the joule rating.

You can get a whole-house surge suppressor if you have extra spaces in your electrical panel for about $300. It installs quickly and easily. But these should be used in combination with the surge suppressing power strips.

I don't think there's any difference between a surge suppressor and a surge protector, but somebody might correct me on this one.
 
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Old 03-10-06, 12:28 PM
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Yep, there's actually two technical ratings important for "surge protectors". Joule is the amount of energy that the device will absorb and not destroy itself. The other is the "clamping voltage". You want a high joule rating and a fairly low voltage rating. There is an IEEE standard that describes the testing of a surge protector, you will find that referenced in advertisement as well.
OK, that said; both joules and clamping voltage talk to the limitations of a surge protector. They work by using devices call Metal Oxide Varistors, (MOV) that have a curious property that allows them to start conducting only when the voltage across their terminals exceed a certain value. All this "extra" surge/electrical energy will get dissipated as heat by the MOV's. Larger MOV and arrays of 3 to 6 or more MOV's in parallel are used to increase this energy (joule) rating. If you exceed the energy rating, the MOV's will overheat; if you exceed this by a large margin, flaming can occur. To prevent large surge events from causing fire in the actual surge protector, the protector itself is typically protected by a fusable element. So, if you are hit with a huge surge, the fuse will blow before the MOV will flame. You are also left with no protection. If you have seen the little green light on the protector, that typically tells you the status of this fuse. The biggest thing to take away from this discussion is that the MOV's have energy limits, and the larger the joule rating is better for you.

The best analogy i can think of right now is a bullet proof vest. Don't expect it to work with a howitzer shell.

Your question of whole house vs. line cord connected protectors is a good one. I personally have a load center protector (under a hundred$), with a high joule rating and a moderate clamping voltage rating. At the point of use of my computer and TV, I use a corded power strip with a smaller joule rating, but a lower clamping voltage rating. So, I expect the load center protector to handle the largest amount of energy, then leaving the corded jobs to deal with the leftovers. Make sense? Also, there is some chance, probably pretty low, that you can pick up surge energy between the load center and the various electronics, so there is some merit in local surge protection.
 
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Old 03-10-06, 12:44 PM
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Adding to Johns reply about whole house surge protection, in my area of the country the utilitiy will hang a whole house surge protector on your meter base. Then you have a couple options you can buy it for about 100 bucks and it belongs to you and you are responsible for replacement costs if it goes bad. Or you can lease it for about $2.50 a month and the utility is responsible for it.

I've always wondered how good the warranties are on the power strips with surge protection if they fail to prevent damage, does anybody know how that works? Seems you would have a heck of a time proving your equipment was damaged because the surge protector failed.
 

Last edited by Roger; 03-10-06 at 12:57 PM.
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Old 03-10-06, 12:52 PM
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Originally Posted by telecom guy
If you exceed the energy rating, the MOV's will overheat; if you exceed this by a large margin, flaming can occur. To prevent large surge events from causing fire in the actual surge protector, the protector itself is typically protected by a fusable element. So, if you are hit with a huge surge, the fuse will blow before the MOV will flame. You are also left with no protection.
Yes, I had one of those surge supressor boxes with a green light (made by DiTeK) installed on A/C circuit. It did caught on fire and was ultimately destroyed by voltage fluctuations during the power surge. Are you saying that after this type of protector/supressor is destroyed, the circuit is not "broken" and is left totally unprotected (and still under load)?
 
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Old 03-10-06, 01:01 PM
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Are you saying that after this type of protector/supressor is destroyed, the circuit is not "broken" and is left totally unprotected (and still under load)?
The little fuse that protects the MOV's are not in line with the load, so yes. The power strip's main job is to provide power, secondly, to clean up surges. If the MOV's are taken off-line, what you have left is unprotected power. This is the case even with load center protectors. Mine is integral, and fits in place of a double pole breaker. Remote boxes are typically fed from a double breaker. In all cases, the protection is put in parallel with the load, not in series with it.
 
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Old 03-10-06, 01:44 PM
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Oh-oh... There were few minutes between the time surge supressor caught fire and the time when I shut down electric panel completely. So, during those few minutes my A/C unit was left unprotected and was bombarded with voltage spikes? Up until now I was hoping that the surge protector had saved my A/C unit. There were no visible signs of damage or burnt smell coming out of it. And because of the cold weather the past couple of months I was not able to check A/C unit operation. But now I am starting to worry...
 
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Old 03-10-06, 04:51 PM
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Don't try to design a surge protector yourself. MOV's are rated by the peak voltage at which they begin to conduct. You actually need something like a 340Volt MOV as the absolute minumum on a 120 volt circuit. Leave the design to the engineers.

Surge protectors are useful to protect delicate circuits like computers from very high voltage, very short duration spikes. While the voltage is high, the energy may often be well within the joule rating of the MOV. If you house takes a direct strike from lightning, nothing is going to totally protect you. Also, if the power company sends a large surge of voltage down the line, the voltage may only be several hundred as opposed to several million, but the energy will be huge, and again a MOV will probably fry. Fuses and circuit breakers will provide crowbar protection in most cases. Also, an undervoltage condition can technically be thougt of as a surge, and of course only a UPS will protect against that.
 
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Old 03-10-06, 06:53 PM
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I would like to add a few things to the already very informative replies:
-Do not confuse a surge protector with a GFCI. I have encountered several clients that have plugged appliances in their bath or kitchen into small surge suppressors, thinking that it was a GFCI.
-I have encountered people that turn off appliances in a thunderstorm. That is not enough. When you turn off an appliance, you are only disconnecting the hot side, not the neutral or ground. It is better to unplug it if you are going to turn it off.
-Don't buy cheap surge suppressors. They are almost worthless. Better ones use more than one method of grabbing those surges.
-Get one with an indicator light. If the light no longer lights, replace the unit.
-Don't forget to protect the telephone and cable lines also.
 
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Old 03-10-06, 07:02 PM
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As a rule of thumb, the closer an arrester is to the device it is protecting, the better job it can do. So as for your question "wholehouse protection vs. individual strips", the best answer would be both. Put the whole house in as general protection for the entire house. Then invest in localized protection for your critical components (PC, Stereo, etc.).
 
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Old 03-11-06, 02:25 PM
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Just to update about my A/C unit. The temperature was in the 70s today so I turned my A/C unit on to check if is working. It does! Apparently the A/C (electromotor, I guess) is using 240V and was not really affected by the "loose neutral" condition that had caused problems throughout my house. The surge supressor that was installed on the 240V A/C circuit was in fact destroyed, but as people already explained me above, it was not really designed to protect from "loose neutral" problems. So, the surge supressor self-destructed under continuos load of fluctuating 240V for a long period of time, but the A/C motor did not even blink. So, now I wonder if the location (or the rating) of the surge supressor unit was chosen wisely by the installers of the A/C unit.
 
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