Does a MOV shunt current or equalize voltage?

No. An MOV is a voltage dependent resistor that has a very high resistance over the normal range of voltages, but its resistance falls dramatically as the voltage rises above the normal range. This conduction helps limit how far above normal the line to line or line to ground voltage terminals of that point in the distribution system can swing by forming a voltage divider between the wiring impedance and the MOV resistance during the over voltage condition.

Unless the MOV arrangement has its own exclusive ground conductor system (available only on some breaker box mounted MOV systems) they have nothing to do with ground, directly. They limit voltage difference between nodes they are connected across by voltage divider action. As long as the connected devices can withstand the voltage within this clamped limit through all possible nodes connected to that device, the MOV has done its job. This may include more than just the line, neutral and ground receptacle terminals, like phone lines or cable TV lines. A useful MOV system should limit all node to node voltage to something below what the protected equipment can withstand. Keep in mind that during a severe surge, all those nodes at the protected equipment might have rather arbitrarily large voltage differences to other non connected nodes, including actual Earth potential.

The MOV is not a short, only a voltage dependent resistance. Assuming it survives the surge, it ceases to conduct significant current the moment the voltage difference across it falls below its rated operating voltage.

"John Doe"

Obvious, as the huge energy available from the AC supply would immediately destroy the MOV.

...... Phil

Such an efficiency with words. And after reading the group, I realize that's a good thing.

Shunts it to where?

Really? Don't they equalize the voltage at the circuit inputs until the transient goes away? How is that the same as "shunting current away from the protected device"?

"John Congenital Dope Head "

( snip pile of brain dead, way OTT abuse )

- needs to be taught a damn good lesson.

Plus kicked off SED for ever.

..... Phil

What you are having for dinner there is off-topic here, Philly.

You couldn't teach a mouse to squeak, you fairy kissing bug muncher.

You need a big dose of reality, Philly, you freaking idiot.

John Congenital Dope Head "

( snip pile of brain dead, way OTT abuse )

- needs to be taught a damn good lesson.

Plus kicked off SED for ever.

What a criminal ASSHOLE.

..... Phil

A MOV is a non-linear resistor, where the impedance decreases substantially above a given ("rated"?) voltage. Not as "sharp" or "abrupt" as a zener. Tends to degrade over useage; if said useage is measured as "dose rate" then degradation seems to be predictable.

MOV's work like zeners but not with the same response range of clamping.. They have a non-linear effect in it's clamp and they do not act like a thyristor to create a crow bar effect either.

They can handle a lot more than a conventional zener does how ever, due to their design the life cycle of these units are limited when getting hit hard enough to perform a heavy clamp even if the clamp fulls with in it's spec.

Those who recommend plug-in protectors do not have electrical knowledge. John Doe demonstrates why some are so easily educated on electricity by retail store salesmen. Posted are samples of his education.

A quote from John Doe's citation which John did not read or understand:

Where is energy in a surge current absorbed? Destructively in appliances if permitted inside the building. Harmlessly if that same current has a short path to earth ground. A protector is only as effective as its earth ground. Instead, some assume the MOV is a complete protection device - absorbs the surge energy.

John Doe saw the number of joules for an MOV. That was sufficient to *know* MOVs protect by absoring the entire surge. He posted that claim often using profanity, as quoted above, as proof. His latest question here: he suddenly learned MOVs do not work by absorbing the entire surge. IOW he is slowly admiting he was wrong. Even John Doe's profanity cannot keep him dumb forever.

A MOV does not have the ability to fully suppress the incoming surge with out destroying it self if it's severe. I think most of us can understand that. The idea is to have a fusable link or protect release circuit that will open in line with the MOV in this case so that it don't get past that point. Yes, the MOV may get and most likely will be destroyed in the process of a major hit how ever, in all cases I have seen the series protection circuit like breakers or fuses have been able to open only because the MOV was doing its job by putting excessive load in the circuit between it and the device its trying to open! Mainly the fuse or breaker.. Normally when a MOV gets destroyed it is shorted permanently but it does make the incoming circuit open as it should unless some one had done a hack repair job or does not know what they are doing!

once this device goes defect, to many times have I seen people just cut them out and replace the fuse instead of replacing both!. moron city!

I my self like using TVS bi-directional diodes to open a fast blow fuse.

. Among those who recommend plug-in suppressors are the IEEE and NIST.

IEEE guide to surges and surge protection:

NIST guides to surges and surge protection:

Both guides say plug-in suppressors are effective. .

. w_ has a religious belief (immune from challenge) that surge protection must use earthing. Thus in his view plug-in suppressors (which are not well earthed) can not possibly work. The IEEE guide explains plug-in suppressors work by CLAMPING the voltage on all wires (signal and power) to the common ground at the suppressor. The voltage between wires to the protected equipment is safe for the protected equipment. Plug-in suppressors do not work primarily by earthing (or stopping or absorbing). The guide explains earthing occurs elsewhere. (Read the guide starting pdf page 40).

Never answered - simple questions:

- Why do the only 2 examples of protection in the IEEE guide use plug-in suppressors?

- Why does the NIST guide says plug-in suppressors are "the easiest solution"?

. Very good answer by Robert Baer. .

. A MOV across a relay coil shunts nothing to ground and protects entirely by voltage limitation, absorbing the energy stored in the relay coil.

-------------------------- An airplane protects equipment from lightning entirely by voltage limitation and not at all by earthing.

---------------------------- For a service panel suppressor, with a MOV from hot to neutral/ground/earthing-electrode-(all connected in US services), say a

(Another critical element of protection in the example above is keeping the ground reference of power and cable and phone at the same potential, even though it is thousands of volts above 'absolute' ground potential. That requires a *short* wire from phone/cable entry protectors to the ground at the power service.)

------------------------------- For a plug-in suppressor, the impedance of the branch circuit 'ground' wire prevents much earthing of a surge. But the impedance of the branch circuit also prevents much surge current, and thus surge energy from reaching the suppressor. The suppressor clamps the voltage on all wires (power and signal) to the common ground at the suppressor. The voltage between wires going to the protected equipment is safe for the protected equipment. Is the protection the voltage limitation (H-N-G) or earthing the surge? Almost entirely from voltage limitation. (See the example in the IEEE guide starting pdf page 40.)

------------------------------- What happens when there is a plug-in suppressor and no service panel suppressor? At about 6,000V (US) there is arc-over from hot bus to panel/ground/neutral/electrode. After the arc is established the voltage across the arc falls to hundreds of volts. That dumps most of the surge energy to earth. Again, because of branch circuit impedance, not much surge energy can reach the suppressor. [There is also arc-over at receptacles at about 6,000V (US)]. In experiments with a MOV at the end of branch circuits 30 ft and longer, with a surge current up to 10,000A, the maximum MOV energy dissipation was 35J. In 13 of 15 cases it was 1 Joule or less. .

. As others have said, MOVs don?t short, they clamp. For power circuits, there will probably always be over 300V (US) across the MOV. High surge currents drive the clamp voltage up significantly.

It is very unlikely there will be a surge current on a hot service wire over 10,000A. Service panel suppressors with much higher ratings are readily available. .

. A surge from lightning will almost always have multiple paths to earth.

On Aug 2, 8:31=A0pm, Jamie

Jamie has posted about things he has seen. He does not post what MOV manufacturers states even in datasheets. MOVs that fail as Jamies has seen are grossly undersized - violate what MOV manufacturers require. Jamie has seen what happens with grossly undersized plug-in protectors that also do not even claim to provide sufficient protection.

Properly sized 'whole house' protector earths a direct strike and remains functional. Effective protectors that remain functional after a direct strike also costs tens or 100 times less money per protected appliance. But those who only know from what they have seen (ie " I have seen the series protection circuit like breakers or fuses have been able to open) did not first learn the science.

Those fuses or circuit breakers are emergency backup proetction when the protector did not do what it is supposed to do. Surges are done in microseconds. Those fuses or breakers open in milliseconds. Those fuses or breakers are to stop a fire because the protector was grossly undersized.

Jamie - go read some manufacturer datasheets. Note the charts so that MOV protectors can be properly sized - do not fail catastrophically. However plug-in protectors often gorssly undersized their MOVs. The myths promoted by that exploding MOV then get the naive to recommend more of those surge protectors.

An effective protector earths direct lightning strikes and remains functional. An effective protector means the human does not know the surge existed. But that would not promote sales of excessively overpriced plug-in protectors.

Relevant are these scary pictures. If the MOVs are grossly undersized, then the protector must fall back upon the emegency safety circuit. Sometimes that safety circuit does not work. These scary pictures result:

Last thing anyone wants is MOVs that routinely fail on that first surge; that must fall back on emergency safety circuits to avoid fire. And yet many who have only seen grossly undersized plug-in protectors feel that dangerous failure mode is acceptable and normal.

Datasheets are quite blunt about this. Catastrophics failure that results in vaporization or shorted MOVs is not listed as acceptable operation. MOVs must be sufficient sized so as to degrade - a 10% voltage change. Those who did not read datasheets - who saw what grossly undersized protectors do - would then post as Jamie has. Those scary pictures are not acceptable - but can happen when the protector is grossly undersized - completely unacceptable.

What A piece of s*it you are, operation of MOV's is common knowledge among those that know what the hell they're doing. This excludes you pecker head!.

what a piece of s*it!, 100% all the way... You know nothing about the subject other than what you think you understand from material you have gotten your hands on.

Try talking from real experience for a change instead of out your ass.

My god, I just hope our current instructors in school teaching this field aren't as dim as you are. God help us all if this is the case.

Please digest better what you read before polluting it all over the place.

We have enough miss guided people already..

. Service panel suppressors are readily available with ratings far higher than the strongest surge that can be reasonably expected.

Plug-in suppressors are not likely to see much of the surge energy because of the impedance of branch circuit wiring and arc-over at the service panel. And very high ratings are readily available. .

. w_ believes service panel suppressors have mega ratings and plug-in suppressors have minuscule ratings. Plug-in suppressors need significant surge capacity to pass UL tests.

Plug-in suppressors with high ratings are readily available and inexpensive. The last plug-in suppressor I bought had 1 MOV that was

. w_ can't understand his own hanford link. It is about "some older model" power strips and says overheating was fixed with a revision to UL1449 that required thermal disconnects. That was 1998. There is no reason to believe, from any of these links, that there is a problem with suppressors produced under the UL standard that has been in effect since

But with no valid technical arguments all w_ has is pathetic scare tactics.

Never seen - a source that agrees with w_ that plug-in suppressors are NOT effective.

Never answered - simple questions:

- Why do the only 2 examples of protection in the IEEE guide use plug-in suppressors?

- Why does the NIST guide says plug-in suppressors are "the easiest solution"?

For real science read the IEEE and NIST guides. Both say plug-in suppressors are effective.

Bud must lie to protect sales of plug-in protectors. Most of those scary pictures are protector manufactured after 1998. And UL1449 standard was crated in August 1985. But must avoid that fact to protect sales. Most every fire company has seen examples of those scary pictures. Where is the worst place to put a protector? On a desktop of papers or behind furniture in dust ball on a rug. This is effective protection? No. But many will spend tens or 100 times more money for protectors that may even create those scary pictures.

UL1449 was created in Aug 1985. Bud must avoid that reality to disparage a serious problem with plug-in protectors - as demonstrates by those scary pictures including a NC fire marshal who explains the problem and resulting fire. Just another reason why the informed homeowner installs only one =91whole house=92 protector from far more responsible companies such as Square D, GE, Siemens, Keison, Leviton, Intermatic, Cutler-Hammer, etc. A protector is only as effective as its earth ground.

Bud is a sales promoter who must post insults to protect those sales. No plug-in protector even claims to provide protection from typically destructive surges. So Bud does not post facts =96 he posts insults. See those scary pictures of protector with UL1449 approval that can still create fire threats.

. w_ got the manufacturing dates from his Ouija board. .

. The village idiot can't figure out the difference between a creation date (1985) and a revision date (1995). .

. Still missing - any source that says suppressors manufactured under UL1449 *2nd edition* (effective 1995) are a problem. .

. Service panel suppressors are a good idea.

What does the NIST guide say? "Q - Will a surge protector installed at the service entrance be sufficient for the whole house? A - There are two answers to than question: Yes for one-link appliances [electronic equipment], No for two-link appliances [equipment connected to power AND phone or cable or....]. Since most homes today have some kind of two-link appliances, the prudent answer to the question would be NO - but that does not mean that a surge protector installed at the service entrance is useless." .

. All of these "responsible companies" except SquareD also make plug-in suppressors.

SquareD, for its "best" service panel suppressor, says "electronic equipment may need additional protection by installing plug-in [suppressors] at the point of use." .

. w_'s religious mantra protects him from evil thoughts (and reality). .

. w_ is so pathetic. .

. Poor sensitive w_ is insulted by reality. Facts:

- Both the IEEE and NIST guides say plug-in suppressors are effective.

- The only 2 examples of protection in the IEEE guide use plug-in suppressors?

- The NIST guide says plug-in suppressors are "the easiest solution"?

- SquareD says "electronic equipment may need additional protection by installing plug-in [suppressors] at the point of use."

Still never seen - a source that agrees with w_ that plug-in suppressors are NOT effective.

For real science read the IEEE and NIST guides. Both say plug-in suppressors are effective.

This is what a sales promoter will do. Distort facts by forgetting something. Effective protection is about earthing before surges can enter a building. Why are modems damaged? Because AC electric is not properly earthed (via a 'whole house' protector) AND because the phone line has a 'whole house' protector. Any wire carrying a surge into the building defeats the entire protection system. Why are modems damaged? Because the surge incoming on AC electric is permitted inside the building AND finds earth ground destructively through the telephone 'whole house' protectors.

What makes this damage easier? What gives that surge a path around protection inside a computer? The plug-in protector. The plug-in protector diverts an AC electric hot (black) wire surge to green safety ground wire. Surge now bypassed protection inside computer's power supply and is connected to directly to computer motherboard. Now a surge has the perfect path to earth ground, destructively, via modem and telephone line 'whole house' protector. Damage made easier because a surge was not earthed BEFORE entering the building.

Bud citation says why a 'whole house' protector does not work. Because all other incoming utilities must also connect to the same earth ground. An AC electric 'whole house' protector is superior protection - makes plug-in protectors redundant - if all incoming utilities wires also have a 'whole house' protectors or a direct earthing connection.

Telcos have installed surge protection on all phone lines long before the PC even existed. Cable TV (if properly installed) makes that earth ground connection without a protector. If these utilities are properly earthed, the one AC electric 'whole house' protector is complete protection.

But again, the protector is only as effective as its earth ground. If the concrete floor is a better conductor that the single point earth ground, then no protector (plug-in or 'whole house') will be effective. A destructive surge seeks the better earth ground. As every responsible source notes, earthing (what a surge is diverted to) defines surge protector effectiveness.

The resp> What these protective devices do is neither suppress

How curious. That quote comes directly from a Bud citation. Bud says plug-in protectors (without earth ground) will do what? It cannot divert that energy to earth? Why must the building have properly earthed 'whole house' protectors? So that plug-in protectors (for example) do not earth surges destructively through the computer's motherboard and modem.

A protector is as effective as its earth ground. What must Bud get you to ignore? Bud claims a plug-in protector (without earthing) will magically make that energy disappear. But even Bud's NIST and IEEE citations say differently. Effective surge protection means that surge energy is earthed before getting to the appliance.

Where is earthing done best? What provides enough protection for every home and for tens or 100 times less money? One properly earthed 'whole house' protector on every incoming utility wire.

Why do better cable companies properly earth their cable before entering a building? Why does that same cable company recommend not using plug-in protectors? Why does the cable (properly installed) already have effective surge protection. It is earth before entering the building.

Why does the telco install a 'whole house' protector on every home where their wires meet yours? Why does the telco also earth their 'whole house' protector to the same earth ground used by AC electric and cable? Again, the best surge protection that also costs massively less money. In every case, the best surge protectors ... "simply divert it to ground, where it can do no harm." Again, from Bud's NIST citation.

Bud hopes you don't grasp the point. If so, you will divert that money (wasted on obscenely overpriced plug-in protectors) on better earthing and a 'whole house' protector. Even plug-in protectors can contribute to appliance damage if the 'whole house' protector is not installed and properly earthed. Bud forgets to mention that part.

Why will I even sell anyone a plug-in protector? Anyone so naive as to through money away - well a $3 power strip with some ten cent parts sells for $25 or $150. The profit margin is so large that anyone will also sell plug-in protectors. But responsible companies (which do not include the scammers such as APC, Belkin, Tripplite, and Monster Cable) sell a lower profit protector that actually provides protection. Only responsible companies, such as GE, Siemens, Square D, Cutler Hammer, Polyphaser, Keison, Leviton, and Intermatic, sell 'whole house protectors.

A protector is only as effective as its earth ground. Therefore every professional discusses what provides surge protection - earth ground. Those 'complete protection' plug-in protectors that do not claim to protect from typically destructive surges (see their spec sheets - it does not even claim such protection) ... Why do sales promoters for those scam artists never discuss earth ground? Plug-in protectors do not have that necessary earthing.

It is called a surge protector. 'Protector' sounds like 'protection'. Therefore it must be surge protection. False. Protection is earth ground. Effective protectors "divert it to ground, where it can do no harm." I am not saying that. Even IEEE and NIST say what the effective protector does - divert surge energy harmlessly into earth. Plug-in protectors 1) do not divert surges to earth and 2) do not even claim to protect from the typically destructive type of surge.

Bud must ignore both points. Sales promoters will say anything to obfuscate facts. Even a plug-in protector can contribute to appliance damage if every incoming utility is not properly earthed. Earth ground is the protection. Every incoming utility wire must be earthed directly or via a 'whole house' protector ... even if using those obscenely overpriced plug-in protectors.

How overpriced? The same protector circuit in the $25 and $150 protectors is also found in the surge protector, selling in a grocery store, for $10. If you need a plug-in protector, then buy the same protector for massively less money - a $10 power strip protector sold in grocery stores - et al. But the same protector selling for less does not pay Bud's bills.

Without proper earthing and a 'whole house' protector, then plug-in protectors can even contribute to electronics, computer and modem damage - as explained up top AND on Page 42 Figure 8 of Bud's citation. Did Bud forget to mention: his plug-in protectors do not even claim to protect from the typically destructive surge? Simply look at its numeric specs. It does not even claim to protect from surge. What kind of protector has no earthing? Ineffective, obscenely overpriced, and promoted by half truths from a sales promoter. See Bud's posts as examples. Even Bud's citations state that earthing (not a protector) provides the protection. A surge protector is only as effective as its earth ground.

The complete answer. One 'whole house' protector will not be sufficient. Every incoming wire must be earthed either directly or via a 'whole house' protector. Properly installed cable and telephone wires already have that protection. The only incoming utility left is AC electric - the most common source of surges AND the only incoming utility that does not automatically have earthed protection. The homeonwer must upgrade earthing to exceed post 1990 code requirements and install one 'whole house' proector. How good is that protection? From IEEE Standards (where IEEE makes recommendations):

No plug-in protector will even dare to predict such protection. The 'whole house' protector is not perfect. After all, protection is only as effective as it earth ground. But at least the 'whole house' protector will not earth a surge, 8000 volts destructively, through adjacent appliances - Bud's citation - Page 42 (of 61) Figure 8. How good is one properly installed 'whole hosue' proetctor? Only 99.5% protection? Did Bud also forget those numbers when posting half truths?

A protector is only as effective as its earth ground. Plug-in protectors do not even claim to provide such protection.

Some people know by learning from datasheets, studying the science and building these things even decades ago - such as this author. Jamie is classic of one who knows only by posting insults.

The properly sized protector should never fall back on those thermal fuses - the emergency protection circuit. But if the MOVs are grossly undersized and if the thermal fuses must trip to protect from fire, then the naive will recommend more of those protectors. The resulting damage gets the naive to promote more grossly undersized (plug-in) protectors.

The effective protector earths direct lightning strikes AND remains functional. MOV manufacture datasheets provide charts to help make this possible. Properly sized 'whole house' protectors earth surges AND remain functional. Those who learn the science know why those thermal fuses are there - to protect from fire when the MOV was grossly undersized - operated in regions that violate manufacturer specs.

No MOV must vaporize or spit flames. The properly sized protector never trips that failure light. That failure light says the surge was massively too large for the protector; so protector abandoned the appliances. Grossly undersized protectors will even indicate failure

- disconnect thermal fuses - when the surge is too small to harm an appliance. All appliances contain internal protection. The surge struck protector and appliance simultaneously. Surge protector was grossly undersized and failed. Protector circuits inside the appliance confronted the same surge and remained undamaged. This causes the naive to promote more grossly undersized plug-in protectors.

If Jamie has basic electrical knowledge, he would have known this AND would have read same in manufacturer datasheets. Instead, Jamie's only reply is insults. Why no quotes from manufacturer datasheets? Jamie does not understand the science. He only saw protectors fail catastrophically and assumed that is normal. When confronted with facts, Jamie can only post profanity. It is also what Jamie understands. It works when the reader does not demand numbers =96 uses profanity as if supporting facts. Jamie never even posts numbers. If he did, then we would learn the extent of his technical knowledge really is. Jamie cannot afford to admit insufficient electrical knowledge =96 and that he never read a datasheet.

Jamie - what you have posted violates what every MOV manufacturer required for normal MOV operation.