Help fix surge protector

[bud--]

bud's job is to promote undersized and extremely profitable protectors.

My only association with the surge protection industry is I am using some surge protectors. If westom had valid technical arguments he wouldn't have to lie.

Meanwhile, the OP is asking for a solution. Not for paperwork that says a fire 'should not' happen.

The "solution" from about everyone is to replace the device.

bud is my personal troll who has followed me for almost ten years posting naysayings.

I first saw westom far less than 10 years ago. But westom has been posting this misinformation for 10 years?

Westom is on a crusade to eliminate the scourge of plug-in protectors. He googles for "surge" to post his beliefs. He has joined an astonishing number of forums to spread his belief that plug-in protectors do not work. Unfortunately almost everything he says about plug-in protectors is wrong.

Its MOVs, on the other hand, are a greater danger. As demonstrates by so many who had their UL1449 protectors catch fire.

Repeating Where is the record of fires in UL listed protectors made since 1998?
Note - UL listed and 1998.

 

[SOFTengCOMPelec]

Repeating Where is the record of fires in UL listed protectors made since 1998?
Note - UL listed and 1998.

Apparently (and in my opinion), not needed!

I investigated the source of information supplied by Westom, earlier in this thread repeated here, for everyones convenience which I have looked into.

It would seem that the existing technology/techniques and standard practices in the US, have a significant tendency to overlook/miss the exact cause of a "surge protector" fire incident.

I'm not blaming the fire investigators, or trying to suggest that they should be changing their procedures. But what I am suggesting is that just because they have not recorded problems with UL1449 (etc), does not necessarily provide proof that there is NO such problem.
Since it may simply have been missed by existing fire investigation procedures.

To me, it seems completely reasonable, that fire investigators are not highly trained Electronics engineers/experts, who know how to forensically examine burnt out MOV evidence, and collect it at the scene. We have to be practicable, about how the work of fire investigations is carried out.

 

[bud--]

Excellent information on surges and surge protection is at:
http://www.lightningsafety.com/nlsi_lhm/IEEE_Guide.pdf
- "How to protect your house and its contents from lightning: IEEE guide for surge protection of equipment connected to AC power and communication circuits" published by the IEEE (the IEEE is a major organization of electrical and electronic engineers).
And also:
http://www.eeel.nist.gov/817/pubs/spd-anthology/files/Surges happen!.pdf
- "NIST recommended practice guide: Surges Happen!: how to protect the appliances in your home" published by the US National Institute of Standards and Technology

The IEEE surge guide is aimed at people with some technical background.

Fuse is the last and emergency protection so that fire does not happen. That failure occurs only when MOVs are grossly undersized.

Because he can't figure out how plug-in protectors work westom believes they are all "grossly undersized".

The normal failure mode for a MOV is to be at low resistance. All UL1449 listed protectors have thermal disconnects, including service panel protectors.

Potentially destructive surges are maybe hundreds of thousands of joules. How many joules in that APC? A few hundred? So where are hundreds of thousands of joules absorbed? That question must always be answered to have effective protection.

As I wrote in a previous post the NIST surge expert, in a published paper, found the amount of energy that can reach a plug-in protector is a maximum of 35 joules, even with the worst surge that has any reasonable probability of occurring. (That worst surge on power wires is a 100,000A lightning strike to a utility pole adjacent to the house with typical urban overhead power distribution.) In 13 of 15 cases it was 1 joule or less. Any protector will have ratings far above that.

There are a couple reasons the energy is so low. One is that when a strong surge raises the service panel busbars to about 6,000V there is arc-over from the busbars to the enclosure. The voltage across the established arc is hundreds of volts. Since the enclosure is connected to the earthing system that dumps most of the surge energy to earth. That is where westom's imagined "hundreds of thousands" of joules go. (But westom just ignores anything that conflicts with his very limited beliefs about surge protection.)

The second reason the energy is so low is because of the impedance of the branch circuit. Since a surge is a very short event the surge current is relatively high frequency. That means the inductance of the branch circuit, which we normally ignore, is much more important than the resistance. You simply can't get a large surge current (and surge energy) on a branch circuit.

Lightning is typically 20,000 amps. More responsible manufacturers provide a 'whole house' protector that is at least 50,000 amps.

Even with the worst case 100,000A strike adjacent to a house the surge current is 10,000A per service wire. High ratings for a service panel protector mean long life, just like high ratings mean a long life for plug-in protectors. Recommended ratings for service panel protectors is in the IEEE surge guide on page 18.

And service panel protectors are a real good idea.
But from the NIST surge guide:
"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."

Service panel protectors do not by themselves prevent high voltages from developing between power and phone/cable wires. The NIST surge guide suggests most equipment damage is from high voltage between power and signal wires.

Service panel protectors are very likely to protect anything connected to only power wires from a very near very strong lightning strike. They do not necessarily protect equipment that also has a connection like phone or cable.

An effective protector does not stop, block, or absorb surges.

Of course not.

But because westom can't figure out how plug-in protectors work he thinks they work by stopping, blocking and absorbing.

Effective protectors connect to what does all (and so effective) protection. Single point earth ground.

Westom believes any protector must directly earth a surge. Since plug-in protectors are not well earthed he believes they can not possibly work. The IEEE surge guide explains (starting page 30) that plug-in protectors do not work primarily by earthing a surge. They work by limiting the voltage on all wires (power and signal) to the ground at the protector. The voltage between wires to the protected equipment is safe for the protected equipment.

When using a plug-in protector all interconnected equipment needs to be connected to the same protector. External connections, like coax also must go through the protector.

More conditions that say why APC will not even discuss earth ground.

That is because plug-in protectors do not work primarily by earthing. As the IEEE surge guide explains, earthing occurs elsewhere in the system.

More responsible manufacturers provide these superior devices. Most are names that any 'guy' would know for their integrity. Including Siemens, Leviton, ABB, Polyphaser, General Electric, Ditek, Square D, and Intermatic.

All these "responsible" manufacturers except SquareD and Polyphaser make plug-in protectors and say they are effective. Westom says plug-in protectors don't work.

SquareD says for their "best" service panel protector "electronic equipment may need additional protection by installing plug-in [protectors] at the point of use."

A protector is only as effective as its earth ground.

It appears to be a religious belief - immune from challenge. Unfortunately for westom, the IEEE surge guide explains how it is not true.

For real science read the IEEE and NIST surge guides. Excellent information on surge protection. And both guides say plug-in protectors are effective.

Then read the sources that agree with westom that plug-in protectors do not work. There are none.

 

[SOFTengCOMPelec]

The normal failure mode for a MOV is to be at low resistance. All UL1449 listed protectors have thermal disconnects, including service panel protectors.

I have not had time to read through all your links yet.
But I thought I would start the ball rolling, by 'questioning' your response.

BUT, the thermal disconnects will have a time delay (it takes time for them to heat up), BEFORE they can disconnect.

But, HUGE sudden transient surges (assuming that the joules available is ENOUGH to overheat the MOV enough, so that it can be a fire risk, max joules may be something we have to argue about elsewhere), are of the order of nanoseconds (can provide link(s) if requested).

Hence the MOV which may need to have been weakened/used-up/too-small/hurt-by-other-surges may have got a huge energy pulse from the very brief surge, to dangerously heat up to a fire starting temperature, BEFORE the thermal cut outs have operated.
(Without testing this out myself, or better understanding MOV's, this is ONLY a theory, I can't say that it is definitely the case yet, but it is what I think some people are trying to say).

 

[westom]

Numerous examples exist of undersized protectors causing house fires. For example, Norma witnessed how easy it can happen in "The Power Outage" in Dec 2008:

Today, the cable company came to replace a wire. Well the cable man pulled a wire and somehow yanked loose their "ground" wire. The granddaughter on the computer yelled and ran because sparks and smoke were coming from the power surge strip.

Only a wiring change created that threat. What happens when a surge is serious? Whitneyd88 describes his fire in 2011 in "My house caught on fire and my tank busted":

A plug caught fire in my room (which was plugged into a surge protecter) it was caused by a power surge and caused my tank to burst.

Fortunately water in his burst aquarium extinguished that fire.

A Boston fire is described in a news report:
http://www3.cw56.com/news/articles/local/BO63312/

The fire was sparked by a surge protector on the second floor. The device is supposed to protect from fires.

Anyone can recognize the problem in the numbers. Protector rated to absorb hundreds of joules can cause a fire if MOVs do not disconnect fast enough. Critical to protecting that protector is an earthed 'whole house' protector.

The NIST brochure demonstrates more problems. Page 42 Figure 8 shows a protector earthing a surge 8000 volts destructively via a nearby TV. Any nearby appliance can be a victim (a destructive path to earth) when an adjacent protector fails to block or absorb that surge. When a protector is too far from earth ground and too close to appliances. The NIST brochure even puts a number to the damage. 8000 volts destructively inside a TV.

Professionals routinely discuss what does protection. The IEEE Red Book says

In actual practice, lightning protection is achieve by the process of interception of lightning produced surges, diverting them to ground, and by altering their associated wave shapes.

All professional organizations define earthing as protection from a typically destructive surge. From the IEEE Emerald Book:

It is important to ensure that low-impedance grounding and bonding connections exist among the telephone and data equipment, the ac power system's electrical safety-grounding system, and the building grounding electrode system. ...
Failure to observe any part of this grounding requirement may result in hazardous potential being developed between the telephone (data) equipment and other grounded items

Risk of fire is less concern. But exists. Not from those 2K resistors that power an LED. From grossly undersized MOVs inside that APC protector. That are dependent only on a fuse to avert a potential fire.

If paid to promote those protectors (ie bud), then one would claim fire cannot happen. Somehow that protector magically makes hundreds of thousands of joules just disappear.

In every facility that cannot have damage (including munitions dumps), damage is routinely averted by connect surges harmlessly to earth. Earth is where hundreds of thousands of joules harmlessly dissipate. But not when using protectors without a dedicated and low impedance connection to earth.

 

[bryanl]

The other transistors likely drive other indicator lights and perhaps latch them.

Those resistors are ordinary, not flameproof. Flameproofs usually have blue bodies.

A resistor run at its rated power will easily reach 100C and eventually discolor, and I believe that's the sole reson those resistors discolored. If you see no other damage in the device, it's highly, highly likely that a surge had nothing to do with the discoloration. If I suspected a surge, I would either return the device to the manufacturer or destroy it.

Here is an indication of the sizes of 1/2W and 1W resistors, shown against 1mm graduations. Don't install 1W resistors if there isn't enough room or if their leads will be too thick for the circuit board. Piggybacking two identical 1/2 W resistors, each twice the resistance of the original, is an acceptable substitute for single 1W resistor, but make good mechanical connections as well as good solder connections.

 

[westom]

A resistor run at its rated power will easily reach 100C and eventually discolor, and I believe that's the sole reson those resistors discolored.

Complete the math. Two 2K resistors on 120 volts means two one watt resistors might dissipate something less than 4 watts. That is a fire hazard. They may not have used flame retardant resistors. But if only two 2K 1 watt resistors, then a fire threat does exist.

Meanwhile, irrelevant here is what they used - even if that 'cost controlled' design creates a risk. Relevant is what is necessary so that that one strip remains safe.

Its transistors also do not latch anything. Transistors only drive that one LED to report on MOV thermal fuse status. To report an emergency safety device tripped to avert fire.

 

[bryanl]

Piggybacking two identical 1/2 W resistors, each twice the resistance of the original, is an acceptable substitute for single 1W resistor,

Complete the math. Two 2K resistors on 120 volts means two one watt resistors might dissipate something less than 4 watts. That is a fire hazard. They may not have used flame retardant resistors. But if only two 2K 1 watt resistors, then a fire threat does exist.

Meanwhile, irrelevant here is what they used - even if that 'cost controlled' design creates a risk. Relevant is what is necessary so that that one strip remains safe.

Its transistors also do not latch anything. Transistors only drive that one LED to report on MOV thermal fuse status. To report an emergency safety device tripped to avert fire.

You're likely right regarding the function of the transistors, but there are three 2K resistors in series, making each dissipate under 1W.

 

[VirtualLarry]

So, Westom, why can't you just do your magic, and ask for multimeter readings, accurate to three digits, and predict if the surge supressor will fail in six months.

At least, that's what you claim for power supplies, that you can predict failures six months out, just by multimeter readings of voltages.

 

[Torn Mind]

So, Westom, why can't you just do your magic, and ask for multimeter readings, accurate to three digits, and predict if the surge supressor will fail in six months.

At least, that's what you claim for power supplies, that you can predict failures six months out, just by multimeter readings of voltages.

In the PSU thread, the multimeter's voltmeter function was being used to measure voltage at an output. A voltmeter is not the proper tool to use in this case as the seen output voltage is not what we're concerned about here. I don't know the details of electrical engineering, but I conjecture the voltage or indicates that something upstream from the output is not performing exactly as it should.

 

[westom]

You're likely right regarding the function of the transistors, but there are three 2K resistors in series, making each dissipate under 1W.

Three resistors must be sized for the potential failure. Meaning each existing half watt resistor dissipates almost one half watt in normal operation. That explains the observed surface cracks and browned PC board.

Those same resistors might dissipate almost one 1 watt in a catastrophic failure mode. So 1 watt would be minimally sufficient. Where I come from, those three 2K resistors HAD to be flame retardant. But then we exceed what is considered safe for homes.

Power strip protectors are made as cheap as possible. Therefore a slightly better design using flame retardant resistors was recommended. However that does not change what is the greater threat. Its grossly undersized MOVs protected only by a thermal fuse.

Three resistor and three transistor circuit monitors MOV thermal fuses. LED only reports a more common failure: fuse blew to protect from fire. Fuse blows because a protector is undersized. Of greater concern than those 2K resistors are its undersized MOVs.

 

[bud--]

I have not had time to read through all your links yet.
But I thought I would start the ball rolling, by 'questioning' your response.

BUT, the thermal disconnects will have a time delay (it takes time for them to heat up), BEFORE they can disconnect.

But, HUGE sudden transient surges (assuming that the joules available is ENOUGH to overheat the MOV enough, so that it can be a fire risk, max joules may be something we have to argue about elsewhere), are of the order of nanoseconds (can provide link(s) if requested).

Hence the MOV which may need to have been weakened/used-up/too-small/hurt-by-other-surges may have got a huge energy pulse from the very brief surge, to dangerously heat up to a fire starting temperature, BEFORE the thermal cut outs have operated.

The MOVs will not heat up any more from a surge at the 'end of life' than from a surge when they are new. And note that the energy that can reach a protector on a branch circuit is actually very limited, as determined by the author of the NIST surge guide, as described in a previous post.

The normal failure mode of MOVs is that they continue to clamp at about the same voltage, but the voltage at which they start to conduct progressively gets lower, until they start to conduct at 'normal' voltages and go into thermal runaway. That happens after the surge is gone. "Time delay" is not a factor.

The NIST surge expert has written:
"In fact, the major cause of [surge protector] failures is a temporary overvoltage, rather than an unusually large surge."
Temp overvoltage is a much longer event and might be caused by crossed power wires.

(If there is a direct lightning strike to the building lightning rods are required for protection.)

 

[bud--]

Numerous examples exist of undersized protectors causing house fires. For example, Norma witnessed how easy it can happen in "The Power Outage" in Dec 2008:

Anyone with minimal knowledge of electronics will recognize that whatever happened (if anything) was not a surge.

And perhaps westom can explain how a service panel protector will provide any protection for whatever happened.

A Boston fire is described in a news report:

Still entirely missing - UL LISTED UL LISTED PROTECTORS MADE SINCE 1998

From westoms previous horror story from a fire department - the text included
"More modern surge suppressors are manufactured with a Thermal Cut Out mounted near, or in contact with, the MOV that is intended shut the unit down overheating occurs."
Wouldn't the author then say if any of the failed protectors were made with thermal disconnects (after 1998).

With no valid technical arguments for why plug-in protectors do not work westom has to resort to scare tactics.

Critical to protecting that protector is an earthed 'whole house' protector.

Nonsense.

But the opposite may be necessary.
SquareD says for their "best" service panel protector "electronic equipment may need additional protection by installing plug-in [protectors] at the point of use."

The NIST brochure demonstrates more problems. Page 42 Figure 8 shows a protector earthing a surge 8000 volts destructively via a nearby TV.

Anyone with minimal mental abilities can discover what the IEEE (not NIST) surge guide says in this example:
- A plug-in protector protects the TV connected to it.
- "To protect TV2, a second multiport protector located at TV2 is required."
- The illustration "shows a very common improper use of multiport protectors"
- In the example a surge comes in on a cable service with the ground wire from cable entry ground block to the earthing system at the power service that is far too long. In that case the IEEE surge guide says "the only effective way of protecting the equipment is to use a multiport [plug-in] protector."
- westom's favored power service protector would provide absolutely NO protection.

It is simply false that the plug-in protector in the IEEE example damages the second TV.

Any nearby appliance can be a victim (a destructive path to earth) when an adjacent protector fails to block or absorb that surge.

Surge protectors do not work by "blocking" or "stopping".

And "to protect TV2, a second multiport protector located at TV2 is required."

When a protector is too far from earth ground and too close to appliances. The NIST brochure even puts a number to the damage. 8000 volts destructively inside a TV.

With even minimal reading ability westom could find that in the IEEE (not NIST) example, without the protector at TV1 the voltage at TV2 is 10,000V. With the protector at TV1 the voltage at TV2 is 8,000V.

But the whole point of the example is "to protect TV2, a second multiport protector located at TV2 is required."

From the IEEE Emerald Book:

Everyone, of course, is in favor of earthing electrical systems. The question is whether plug-in protectors are effective.

With minimal reading ability westom could find the "Emerald" book recognizes plug-in protectors as an effective surge protection device. The "Emerald" book is about protecting sensitive electronics.

If paid to promote those protectors (ie bud)

The lie repeated. Aren't personal attacks a violation of the TOS?
If westom had valid technical arguments he wouldn't have to lie.

Somehow that protector magically makes hundreds of thousands of joules just disappear.

It is only magic for westom. He ignores my explanation of where the energy goes (which originally comes from the NIST surge expert). Just like he ignores the explanation of how plug-in protectors work in the IEEE surge guide (staring page 30).

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

Then read the sources that agree with westom that plug-in protectors do not work. Still entirely missing.

 

[SOFTengCOMPelec]

The MOVs will not heat up any more from a surge at the 'end of life' than from a surge when they are new. And note that the energy that can reach a protector on a branch circuit is actually very limited, as determined by the author of the NIST surge guide, as described in a previous post.

The normal failure mode of MOVs is that they continue to clamp at about the same voltage, but the voltage at which they start to conduct progressively gets lower, until they start to conduct at 'normal' voltages and go into thermal runaway. That happens after the surge is gone. "Time delay" is not a factor.

The NIST surge expert has written:
"In fact, the major cause of [surge protector] failures is a temporary overvoltage, rather than an unusually large surge."
Temp overvoltage is a much longer event and might be caused by crossed power wires.

(If there is a direct lightning strike to the building lightning rods are required for protection.)

Good answer!

Your reply makes a lot of sense to me, I had not taken enough consideration into the gradual failure mechanisms of MOV's.

Thanks for the reply.

 

[westom]

I had not taken enough consideration into the gradual failure mechanisms of MOV's.

Put numbers to that degradation. A maximum Vb voltage change for any MOV is 10%. A voltage change this small means no visual indication (ie no burned MOVs). A greater voltage change means a catastrophic (unacceptable) failure (ie fire) often seen with undersized power strips. Also called thermal runaway. bud has described that catastrophic failure as if it was acceptable.

If an MOV threshold voltage changes more than 10%, then that protector was grossly undersized. And a potential fire. Only failure mode also reported by the OP's indicator light (with 2K resistors) is a catastrophic (unacceptable) failure. That light cannot report the other and acceptable degradation (a 10% voltage change).

An MOV manufacturer's datasheet describes how to test this normal (acceptable) failure mode. Note the numbers.

The change of Vb shall be measured after the impulse listed below is applied 10,000 times continuously with the interval of ten seconds at room temperature.

10,000 times? If an MOV is properly sized, then its voltage does not change by 10% after many surges. An application note from Littlefuse says same:

A "failed" device is defined by a +/-10% change in the nominal varistor voltage at the 1mA point.

The unacceptable and catastrophic failure mode (thermal runaway) must never happen. As in never.

A fire threat does not exist when the protector is properly sized so that degradation (voltage change) is well less than 10%. Numbers say no appreciable degradation after many surges over many decades.

MOVs with burn marks or any other physical deformities seriously exceeded MOV manufacture's requirement for safe operation. When undersized and when its fails catastrophically, then naive consumers recommend them as 'one shot' protectors. Failing prematurely (being undersized) promotes sales.

An indicator light (with 2K resistors) originally discussed by the OP only reports a thermal runaway - due to being undersized.

bud's expert says adjacent (point of connection) protectors can even make appliance damage easier. We, who did this stuff as engineers for decades, have identified similar damage created by an adjacent protector. Martzloff says in a conclusion to his 1994 IEEE paper:

Conclusion:
1) Quantitative measurements in the Upside-Down house clearly show objectionable difference in reference voltages. These occur even when or perhaps because, surge protective devices are present at the point of connection of appliances.

Critical is for MOVs to be properly sized so that degradation (voltage change) remains less than 10% after numerous surges. (IOW earth a properly sized 'whole house' protector). Critical is protectors distant from appliances and low impedance (ie 'less than 10 feet') to single point earth ground. These superior, properly sized, and less expensive solutions are provided by manufacturer's with better integrity. Then hundreds of thousands of joules dissipate harmlessly outside the building.

Energy that dissipates harmlessly outside does not change MOV voltages by more than 10%. Does not create thermal runaway. Properly sized MOVs must not exceed the 10% voltage change after those 10,000 surges. Protector voltages become more than 10% lower (and can suffer thermal runaway) when undersized.

The 2K resistors were a less threat. MOVs in that APC protector are undersized. So undersized that the protector must be protected by properly earthing a 'whole house' protector. Because thermal runaway is the reason for so many house fires.

 

[SOFTengCOMPelec]

Put numbers to that degradation. A maximum Vb voltage change for any MOV is 10%. A voltage change this small means no visual indication (ie no burned MOVs). A greater voltage change means a catastrophic (unacceptable) failure (ie fire) often seen with undersized power strips. Also called thermal runaway. bud has described that catastrophic failure as if it was acceptable.

If an MOV threshold voltage changes more than 10%, then that protector was grossly undersized. And a potential fire. Only failure mode also reported by the OP's indicator light (with 2K resistors) is a catastrophic (unacceptable) failure. That light cannot report the other and acceptable degradation (a 10% voltage change).

An MOV manufacturer's datasheet describes how to test this normal (acceptable) failure mode. Note the numbers. 10,000 times? If an MOV is properly sized, then its voltage does not change by 10% after many surges. An application note from Littlefuse says same: The unacceptable and catastrophic failure mode (thermal runaway) must never happen. As in never.

A fire threat does not exist when the protector is properly sized so that degradation (voltage change) is well less than 10%. Numbers say no appreciable degradation after many surges over many decades.

MOVs with burn marks or any other physical deformities seriously exceeded MOV manufacture's requirement for safe operation. When undersized and when its fails catastrophically, then naive consumers recommend them as 'one shot' protectors. Failing prematurely (being undersized) promotes sales.

An indicator light (with 2K resistors) originally discussed by the OP only reports a thermal runaway - due to being undersized.

bud's expert says adjacent (point of connection) protectors can even make appliance damage easier. We, who did this stuff as engineers for decades, have identified similar damage created by an adjacent protector. Martzloff says in a conclusion to his 1994 IEEE paper:
Critical is for MOVs to be properly sized so that degradation (voltage change) remains less than 10% after numerous surges. (IOW earth a properly sized 'whole house' protector). Critical is protectors distant from appliances and low impedance (ie 'less than 10 feet') to single point earth ground. These superior, properly sized, and less expensive solutions are provided by manufacturer's with better integrity. Then hundreds of thousands of joules dissipate harmlessly outside the building.

Energy that dissipates harmlessly outside does not change MOV voltages by more than 10%. Does not create thermal runaway. Properly sized MOVs must not exceed the 10% voltage change after those 10,000 surges. Protector voltages become more than 10% lower (and can suffer thermal runaway) when undersized.

The 2K resistors were a less threat. MOVs in that APC protector are undersized. So undersized that the protector must be protected by properly earthing a 'whole house' protector. Because thermal runaway is the reason for so many house fires.

Disclaimer: I am giving you a quick/rough answer, which SHOULD NOT be used when designing equipment etc. I would have to spend much more time researching this, performing bench experiments and possibly referring to experts in this and other fields.

I think there may be some confusion over the usage of the term "Thermal runaway".

The MOV wiki Also called Varistor gives the following quote:

In general, the primary case of varistor breakdown is localized heating caused as an effect of thermal runaway. This is due to a lack of conformity in individual grain-boundary junctions, which leads to the failure of dominant current paths under thermal stress.

I am taking the "thermal runaway", in the above quote to mean that a tiny part of the MOV, so happens to have a slightly lower "trigger" voltage, than the rest of the MOV.
This means that when a 'surge' hits the MOV, the tiny (slightly reduced trigger voltage) section, begins to absorb, almost ALL of the incoming surge.
As this progresses, the same tiny section of the MOV gets, rapidly hotter and hotter, and its resistance gets lower and lower, i.e. you get a tiny section, where 'thermal runaway' of that tiny section, has caused the tiny bit to get extremely hot, and "burn away".
So the use of the term 'Thermal runaway' is trying to describe the "wearing out" mechanism of MOV's, NOT a dangerous MOV overload situation.

A non-UL1449, very poorly made surge protector, with a tiny MOV, when given a HUGE surge, may indeed have a (potentially dangerous) MOV overload and possible fire hazard. This can also be called "thermal runaway", because of the rapidly reducing resistance, as the MOV temperature goes through the roof. (Which reminds me of second breakdown in bipolar power transistors).
But this type of "thermal runaway", should not be confused with the "thermal runaway" nature of MOVs wearing out by repeated surges.

In the ideal world ALL surge protectors would have really big, high rated MOVs, such that they could withstand 10,000's of big surges, suffering from little or no damage.
But in practice, this would make surge protectors more expensive, quite possibly so expensive that most people would not be interested in buying them anymore.

Therefore the realistically priced surge protectors, which many people buy, have smaller MOVs, which don't give the huge lifetime of big MOV surge protectors.
But that does not necessarily mean, that with the correct, safety improving UL1449 techniques, all or most of the safety, can be designed back in to the standard sized MOV surge protectors.

UL1449 might mean that the MOVs parameters (voltage rating) changes by more than the 10% datasheet value, and hence can be declared faulty.
But if UL1449 has got sensible safety features built in, such as thermal protection, fuse(s) and safety indicator lights, then the situation can still be safe (assuming the UL1449 design features work ok).

One thing that does make me a bit concerned is that the user is expected to regularly check the 'safety' LED lights, so that they know when the useful life of the surge protector, is used up.
My personal view is that many users will either NOT realize they need to regularly check the lights, or they will simply forget or not bother to check them.
I.e. I would prefer UL1449 surge protectors to NOT rely on the user regularly checking these (led) lights, as part of the safety case of surge protectors.

 

[westom]

In the ideal world ALL surge protectors would have really big, high rated MOVs, such that they could withstand 10,000's of big surges, suffering from little or no damage.
But in practice, this would make surge protectors more expensive, quite possibly so expensive that most people would not be interested in buying them anymore.

That is what a 'whole house' protector does. Properly sizing MOVs are in protectors that actually do protection. That even earth direct lightning strikes and remain functional.

The other and different device, also called a protector, is often a profit center. MOVs in them are only more robust when UL 1449 is requires it. Take a $3 power strip. Add some ten cent protector parts. Sell if for $25 or $40. Monster has a long history of duplicating this design, making it look expensive, and then selling their products for $80 or $120. A profit center that does not even claim to protect from typically destructive surges such as lightning.

Once that thermal runaway starts inside an MOV, typically, heat then causes the entire MOV to fail catastrophically. A fire marshal describes how this happens. And why investigators overlook the reason:
http://www.esdjournal.com/techpapr/Pharr/INVESTIGATING SURGE SUPPRESSOR FIRES.doc

Recent fires involving multiple outlet devices toted as surge suppressors raised attention at the Gaston County Fire Marshal’s office primarily when one such fire occurred in a fire station. Investigation of a fire that started behind a desk in an office revealed the ignition source was a surge suppressor. ...
Alternatively, fire investigators m[a]y correctly determine the suppressor was involved in ignition but improperly categorize the cause as overloading or other related failure initiated by the user.

He also says why fire occurred.

. ... workers were attempting to connect an emergency generator to the firehouse's electrical system to provide an alternative electrical source. Workers noted problems with the system and later, after the fire, discovered the generator was shipped from the factory with a loose neutral (a condition that causes voltage differences between legs of a 120 volt electrical system). Fire fighters noted fluctuations in their radio and other electronics thus started to disconnect all electronics from the system. In the office area they discovered a small fire burning behind the desk.

Others have seen trivial anomalies create fire when protectors are undersized; are not even designed for typically destructive transients. Norma in 2008 describes the danger:

Today, the cable company came to replace a wire. Well the cable man pulled a wire and somehow yanked loose their "ground" wire. The granddaughter on the computer yelled and ran because sparks and smoke were coming from the power surge strip.

All he did was disconnect a wire to only damage the protector. Fire occurs without damage to other appliances from anomalies that otherwise have no indication (ie no other appliance damage). Whitneyd88 in Mar 2011 describes a fire:

A plug caught fire in my room (which was plugged into a surge protecter) it was caused by a power surge and caused my tank to burst. ... We're lucky the fire started right next to the tank because when it busted it instantly put the fire out. So the only damage besides a torched wall and flooded room was soot covering everything all over the house.

UL1449 was created in 1986 because undersized protectors caused so many fires. The threat continued. So UL 1449 was upgraded twice over. But fires occur even after the latest upgrades.

A protector must be rated to earth direct lightning strikes and remain functional. Then fire risk is minimized. And that protector is actually protecting from what otherwise causes appliance damage. We don't scatter undersized protectors all over a building - spending $thousands. We earth one properly sized protector so that a surge does not even enter the house. For protection from all types of surges. For about $1 per protected appliance. So that the protector makes another 'always required' connection: a low impedance (ie 'less than 10 foot') connection to single point earth ground.

A protector that does not degrade by 10% does not (almost arbitrarily) create fires. Typically does not go into thermal runaway if its voltage does not change more than 10%. Its 'catastrophic failure' light needs no frequent inspection. In fact, one friend had 33,000 volts drop onto local distribution so that even electric meters exploded from their pans. Others had numerous appliance and protector damage. At least one had fused circuit breakers. He only had a damaged meter; nothing else. Even the 'whole house' protector's light did not report damage. Because his one and only protector was properly sized. But more important - properly earthed.

OP's APC is a perfect example of a protector undersized as to (rarely but) sometimes cause house fires. Those three 2k resistors are not the threat. Undersized MOVs create a greater risk.

BTW, parallel bipolar transistors because thermal runaway is not problematic. However Fet transistors exhibit catastrophic failure due to thermal runaway. We learned this stuff the hard way over many decades.

 

[sm625]

I was taught that a resistor must be sized to provide double the maximum dissipation.

Given the fact that they are only 1.5 watts total, the circuit was clearly not designed to handle 120V. In order to safely dissipate 120V @ 20 mA you need 2.4W (*2 for safety margin) of resistors. That is 4.8W, yet this circuit only has 3 half watt resistors. Oops. Even if they were each 1 watt resistors, it would still be eating into the safety margin.

To fix that design issue you could replace each of those three 2K resistors with two 1K half watt resistors in series. Those are fairly common parts. But you can use whatever values you want, as long as together they provide 6Kohms and about 5 watts.

 

[SOFTengCOMPelec]

I was taught that a resistor must be sized to provide double the maximum dissipation.

Given the fact that they are only 1.5 watts total, the circuit was clearly not designed to handle 120V. In order to safely dissipate 120V @ 20 mA you need 2.4W (*2 for safety margin) of resistors. That is 4.8W, yet this circuit only has 3 half watt resistors. Oops. Even if they were each 1 watt resistors, it would still be eating into the safety margin.

To fix that design issue you could replace each of those three 2K resistors with two 1K half watt resistors in series. Those are fairly common parts. But you can use whatever values you want, as long as together they provide 6Kohms and about 5 watts.

I think it's likely that most people's calculations in this thread, as regards the resistors are incorrect.
I have NOT seen its schematic, but, because transistors are involved, and especially the led, it is VERY likely to be DC rectified (probably by the diode I think I can see, nearby).
This halves the power dissipation, because the resistors will only see a significant current, every other AC cycle.

You may well have been taught that doubling the resistor dissipation is a good idea. But in real life electronics industry practice, they want to save money, and high rated components cost a lot more (usually).
Therefore, although there may be some kind of safety margin, they were probably designed on purpose to be those values.

It may well be DANGEROUS to increase the ratings of those resistors, because they may be intended to "burn out" open circuit, rather than set the unit on fire.
A quick and rough look by me, would seem to indicate they are some kind of flame resistant or flame proof resistor, but I am not 100% sure, as I don't have enough information available to be 100% sure.
But the other resistors appear to be normal resistors.

I still say, play safe, and bin it.

 

[westom]

I was taught that a resistor must be sized to provide double the maximum dissipation.

Fire risk is lower than from the other more common reason for fire. However that risk is why I recommended flame retardant resistors or a tiny fuse. Manufacturer did not consider risk high enough to spend a few more pennies even on one watt resistors.

 

[westom]

I have NOT seen its schematic, but, because transistors are involved, and especially the led, it is VERY likely to be DC rectified (probably by the diode I think I can see, nearby).

Correct. If I remember, it was a 1N4005 diode. However design so that a one part failure does not cause a catastrophic event. Should the diode fail shorted, then what happens to those resistors? Diode is more likely to fail during a higher and normal voltage. Again, the risk is tiny compared to another. But it does exist.

Those three 2K resistors at half watt were the tiniest they could have used. Remember the objective of that type product - that does not even claim to protect from typically destructive surges.

 

[SOFTengCOMPelec]

That is what a 'whole house' protector does. Properly sizing MOVs are in protectors that actually do protection. That even earth direct lightning strikes and remain functional.

If any of the following were done, they would be likely to save lives:

• Put more air bags and other safety devices in cars
• Double the number of hospitals and number of Doctors available
• Give everyone $1000 a year to spend on improving their health, wellbeing and safety
• Double the size of all law enforcement capabilities
• Reduce the AC voltage down to 9 Volts for safety sakes
• Put RCD and other safety devices into all electrical AC plugs and sockets
• Give every household a free annual AC supply health and safety check, including grounding of all sockets

Basically the above things are not done for three main reasons,
which are, cost, cost and cost.

So the problem is it would cost too much money to give every household incoming AC supply surge protection, and/or people are not interested enough in it to have it done and/or any possible life saving is not big enough to justify the cost and hassle involved.

I'm not convinced that it would be that cheap, because if the unit was FREE, it would still cost a small fortune to get a qualified electrician to fit the all house surge protectors.

----------------------------------------------

But I don't know the exact costs and/or cost/benefit.
So it could be a worthwhile thing (All home AC surge protection), I'm not really in a position (at the moment) to know the answer for certain.

BTW, parallel bipolar transistors because thermal runaway is not problematic. However Fet transistors exhibit catastrophic failure due to thermal runaway. We learned this stuff the hard way over many decades.

Fets (everything else fixed, temperature rises) resistance (Rds on), rises with increasing temperature. So paralleled up Fets, will usually work out ok (with some exceptions, including REALLY sudden transients, although even those may well be ok).
BUT bipolar transistors, unfortunately, reduce their resistance (strictly speaking the voltage drop gets reduced between emitter and collector, as the "gain" of the bjt (Hfe) increases), meaning that paralleled up bipolar transistors, DO potentially suffer from thermal runaway.
But there are plenty of circuit solutions to minimise the problem, and thermally connecting them together (e.g. sharing a heatsink), usually helps a fair bit.

Depending on circuit configuration Fets and/or Bjt (Bipolar Junction Transistors) can both exhibit thermal runaway, but generally Fet's are considered free of it, and Bjt considered prone to it.

Really it was VERY old electronics from the 1960's and older which tended to especially have thermal runaway problems, because the Germanium transistor technology of the time, was VERY prone to it, because of the characteristics of Germanium, which I will not go into here.

 

[westom]

So the problem is it would cost too much money to give every household incoming AC supply surge protection, and/or people are not interested enough in it to have it done and/or any possible life saving is not big enough to justify the cost and hassle involved.
I'm not convinced that it would be that cheap, because if the unit was FREE,

The best solution even sold in Lowes and Home Depot for less than $50. Costs: about $1 per protected appliance. This superior and less expensive solution has been routine in facilities that cannot have damage. Why are power strips banned from some of these facilities? ie Munitions dumps cannot have that risk.

Cost is irrelevant. Value is relevant. Bean counters only worry about costs. Therefore create a short term cost reduction followed by massive cost increases. Costs are only reduced when using innovation. When using cost as one parameter to something far more important - value. A major difference between bean counters who destroy companies verses product people who make prosperous companies. Cost controls usually result in increase costs. Only innovation reduces costs.

Again, a solution to averting house fires is one protector that costs tens of 100 times less money. And that is routinely available from other more responsible companies - for decades. About $1 per protected appliance. That friend who had a 33,000 volt fault? His 'whole house' protector originally cost $39. Today, it costs slightly more. And remains about $1 per protected appliance.

It's not just a good idea. It should be installed in every facility. But again, a protector is not so important. A connection to and quality of earth ground makes it so successful. Protectors are simple science. A protector that is a fire risk identifies a bean counter foolishly using cost controls. Because the superior solution also costs tens or 100 times less money. Provided by companies known for their integrity.

 

[SOFTengCOMPelec]

The best solution even sold in Lowes and Home Depot for less than $50. Costs: about $1 per protected appliance. This superior and less expensive solution has been routine in facilities that cannot have damage. Why are power strips banned from some of these facilities? ie Munitions dumps cannot have that risk.

Cost is irrelevant. Value is relevant. Bean counters only worry about costs. Therefore create a short term cost reduction followed by massive cost increases. Costs are only reduced when using innovation. When using cost as one parameter to something far more important - value. A major difference between bean counters who destroy companies verses product people who make prosperous companies. Cost controls usually result in increase costs. Only innovation reduces costs.

Again, a solution to averting house fires is one protector that costs tens of 100 times less money. And that is routinely available from other more responsible companies - for decades. About $1 per protected appliance. That friend who had a 33,000 volt fault? His 'whole house' protector originally cost $39. Today, it costs slightly more. And remains about $1 per protected appliance.

It's not just a good idea. It should be installed in every facility. But again, a protector is not so important. A connection to and quality of earth ground makes it so successful. Protectors are simple science. A protector that is a fire risk identifies a bean counter foolishly using cost controls. Because the superior solution also costs tens or 100 times less money. Provided by companies known for their integrity.

$50 does not sound too bad, and if it was fitted on a new house build, when a major home rewiring is taking place, or other major works, it should not cost too much to fit.
I guess it needs legislation, but I'm not qualified (as regards AC surge stuff etc) and don't know the finer details, to be able to determine how important it is to get this legislated and/or persuading people to have them fitted.

Your latest arguments have made me tempted to go for all home AC surge protection, if I was in that position.

It makes sense that there would be plenty of companies who want to make money from selling small, plug in surge protectors.

 

[westom]

I guess it needs legislation, but I'm not qualified (as regards AC surge stuff etc) and don't know the finer details, to be able to determine how important it is to get this legislated and/or persuading people to have them fitted.

Codes (ie legislation) only addresses human safety issues. It does not address transistor safety. That difference is critical.

First, no protector does protection. Protection (be it using a lightning rod or a protector) is defined by the quality of and connection to earth. Earth is where hundreds of thousands of joules are harmlessly absorbed. Critical to any surge protector is a low impedance (ie 'less than 10 foot') connection to single point earth ground. An electrode that both meets and exceeds code requirements.

For example, if a breaker box ground wire goes up over the foundation and down to earthing electrodes, then protection is compromised. Wire length (not thickness - length) is too long. Sharp bends exist going over the foundation. Ground wire is not separated from non-grounding wires. Better protection connects a 'whole house' protector on a wire through the foundation. Eliminating feet of wire. No sharp bends. And separated from other wires above the breaker box.

Second, a key term is "single point earth ground". A utility demonstrates good, bad, and ugly (preferred, wrong, and right) solutions.

A minimal 50,000 amp number for a 'whole house' protector defines life expectancy over many surges. Quality of that earthing and its connection define protection during each surge. Most important component of any protection system is its earth ground. Not just any earth ground. A low impedance connection to "single point earth ground". That addresses both equipotential and conductivity.

Code and legislation do not address 'transistor safety'.