surge protector upgrade (adding MOV's to raise the joules rating)

[Guest " "]

here's your typical surge protector.

[Guest " "]

inside, there are flate waffer devices about the size of a dime called MOV's that absorb surges. I count three in this one.

[Guest " "]

the MOV's look tike this.

[Guest " "]

just happen to have a box of them. when I run my power tools, I blow these like pop corn. even if they don't pop, they don't last very long in normal use. The more surges you get, the shorter their life is. they have a memory.

[Guest " "]

we are going to slide 3 of them into these holes. this will basically double the joules rating of the surge protector. In a 4 outlet protector, I can slide 5 more into them. this one is a 3 outlet protector.

[Guest " "]

folding the leads so they are 1 inch apart helps, and a good set of needle nose pliers

[Guest " "]

they slide right into the holes. the leads lock once they get in about 3/8's of an inch. cover goes back on, and thats it. This is the last one. did 10 of them this morning.

[Guest " "]

I got a few PM's about this.....just have someone check your surge protector for the insert holes and enough clearance for a dime to stand up.....if you got the know how...PM me your address and I'll send you some MOV's. If your not electrically inclined, find someone who is and let me know.

[Guest " "]

Here's a 4 out let version....

[Guest " "]

fold the leads on 5 MOV's.....

[Guest " "]

slide them into the locking holes with a good pair of needle nose pliers.....

[Malcolm]

Well, they certainly shouldn't fail now. Any reason you are using S20K250's? Those are 250V parts. The originals are likely 130V parts. Maximum clamping voltage is something like 650V v. 170V.

FWIW paralleling MOVs doesn't necessarily resultant in a corresponding increase in the surge current the device can handle. The MOVs have to be closely matched to do that. If not, it is possible that a single MOV will handle most or all of the current. MOV manufacturers offer closely match MOVs, but it is special order. The S20K250 is plus or minus 10% which might be problematic. Paralleling MOVs does provide redundancy, though. If one fails, there are still others to do the job.

[Guest " "]

Well, they certainly shouldn't fail now. Any reason you are using S20K250's? Those are 250V parts. The originals are likely 130V parts. Maximum clamping voltage is something like 650V v. 170V.

250's are good for 110 or 220. a 130 would be clamping all day long since NYC voltage is 126 - 132 volts.

[Malcolm]

..a 130 would be clamping all day long since NYC voltage is 126 - 132 volts.

Perhaps in some some cases, usually not. Depends on where the varistor voltage of the part falls in the distribution.

OK, so why not use a 140V part, or something else in between that and 250V? Seems like using a 250V part is much more conservative than necessary from the standpoint of reliability, and pushing your luck as far as protection goes. The MOVs in my whole-house surge protector are 150V parts and have lasted 10 years. Of course, they are 40mm parts, not 20mm parts like in your strips.

[Guest " "]

Malcolm

I appreciate your suggestions. But the 250's are specified for both 110/120 and 220/240. The're fine in a 130 volt circuit. I didn't take out the MOV's in the earlier stages I think those are in between 130 and 250, these were added in the last stage. I also have 6 60mm MOV's (90 bucks each) that I installed in my main panel and my sub panel.

[westom]

You are doing some of what I did many decades ago to learn this stuff. Appreciate from numbers what has been created.

First, destructive surges are typically hundreds of thousands of joules. How do hundreds of joules in those MOVs absorb surges that are hundreds of thousands of joules. They don't. Surges too tiny to harm appliances can destroy undersized protectors. Effective protectors means even direct lightning strikes. And the protector remains functional. Unfortunatley, when a protector must absorb hundreds of thousands of joules, then a fire hazard exists. Some pictures demonstrate the threat:

http://www.ddxg.net/old/surge_protectors.htm
http://tinyurl.com/3x73ol entitled "Surge Protector Fires"
http://www3.cw56.com/news/articles/local/BO63312/
http://www.nmsu.edu/~safety/news/lesson-learned/surgeprotectorfire.htm
http://www.pennsburgfireco.com/fullstory.php?58339

Protectors are not sacrificial devices. But are promoted that way to sell power strip protectors with obscene profit margins. Protection is always about where energy dissipates. A concept understood by over 100 years of well proven science. A protector is only as effective as its earth ground.

Using protectors in that manner caused so many fires that UL 1449 (1st edition) was created. Kudos for trying things to learn. But move forward. Using MOVs as shown is also a threat to human life.

How do protectors absorb hundreds of thousands of joules? The solution is found in that statement. A protector is only as effective as its earth ground. Which is why effective protector makes a connection as short as possible (ie 'less than 10 feet') to single point earth ground. A protector must earth even direct lightning strikes. And remain functional. Those MOVs fail catastrophicially because voltage exceeded something like 800 or 900 volts.

So why did the appliance not fail? About 1970, electronics had to withstand 600 volts without damage. Today those standards are hundreds of thousands of volts. Destructive surges typically occur once every seven years. A number that will vary signficantly even within the same town. Any 1000+ volts surge will blow through both protectors and appliance. Effective protection means the typically destructive surge must not even be inside the building. Protection is always about where energy (hundreds of thousands of joules) dissipates. A protector is only as effective as its earth gorund. And must not even fail catastrophically as even MOV manufacturer defined in datasheets. An MOV that fails catastroohically is even a threat to human life as well as not provide effective protection.

[Guest " "]

westom, sure, I have seen MOV's blow, thats why I only use surge protectors made of heavy gauge metal. I learned the hard way the surges power tools can generate be it mine or other home owners on my local transformer. Lighting, sure, we get plenty, and before dressing out the place with point of entry and local surge protection we have had our share of blown laptops, TV's, peripherals.

[Malcolm]

Malcolm

I appreciate your suggestions...

Actually, I wasn't suggesting anything. I am just tying to follow your logic in doing something at odds with most manufacturers of surge protectors. Of course 250V MOVs are fine in a 130V circuit. But you wind up with a much higher clamping voltage. Surges below 600V or so are not an issue for you?

FWIW it sounds like you live in one hell of a neighborhood, electrically, that is. I read somewhere that most MOV failures are not due to surges, but sustained over-voltage situations. Using a higher voltage rating would help with that.

[westom]

I have seen MOV's blow, thats why I only use surge protectors made of heavy gauge metal. I learned the hard way the surges power tools can generate be it mine or other home owners on my local transformer..

Any protector that fails did no protection. Is considered a threat to human life. Protectors with blown MOVs are mostly to promote mythical protection to naive consumers. Effective protection means all surges - even direct lightning strikes - cause no protector damage.

Appliances do not create surges for a long list of reasons. If they did, then you are replacing dimmer switches and digital clocks daily. What some consider surges are only noise. If an appliance is generating surges, then a first thing destroyed is what is closest to that surge generator. Itself.

Always use blown laptops, TV's etc to learn both the incoming and outgoing paths through that appliance. Learn from each failure. For example, modems and answering machines are most often damaged by surges incoming on AC mains. Outgoing via a telephone line (due to the always existing connection to earth). Without both incoming and outgoing paths, then no surge damage can exist.

Most will see a destroyed modem. Then assume a surge entered on its phone line. Assume rather than remember what is always required to have electricity - the always required incoming and outgoing path.

Protection is always about the current. And a low impedance connection to what the surge seeks. Low impedance is another critically important factor. Explains why effective protectors make that short (ie 'less than 10 foot') connection to earth. Impedance is also why a protector is more effective when distant from protected electronics.

Effective protection means a protector must not fail. Protecting even the furnace and bathroom GFCIs. And is located where failure will not threaten human life. Protectors should not be on a desktop covered in papers. On a rug. Or behind some furniture. Just another reason why effective protection is located at a service entrance (ie in a breaker box or on the meter pan).

. In one case, a 33,000 volt wire fell upon local distribution. Electric meters literally exploded 30 feet from their pans. Many homeowners with plug-in protectors had numerous appliance and protector damage. At least one had failed circuit breakers. But my friend knows someone who knows this stuff. He had one 'whole house' protector properly earthed. Other than a damaged meter, he had no other damage. Even his 'whole house' protector remained functional.

Just because you have seen protectors destroyed does not mean that is acceptable or protection. MOV manufacturer data sheets define such catastrophic MOV failures as unacceptable. Must not happen. What may happen when protectors are grossly undersized or not properly designed. Made even worse if located where fire is easiest. Your examples are how protectors were designed before 1985 - before safety standards made that catastrophic failure unacceptable.

Effective protection means even direct lightning strikes exist without anyone knowing a surge existed. Even the protector must not fail.

While at it, also experiment with bi-directional avalanche diodes (ie Transorbs) rated at above 185 volts for 120 volt operation. A number obvious if relevant parameters are understood. Also learn an important difference between longitudinal and normal mode currents.

[mark1101]

I'd like to see a consumer electronics protector that can take a direct lightning strike and still function. I don't believe one exists. A direct lightning strike will destroy most anything. We have one of those protectors on our electric meter and it got hit once and sacrificed itself to save our large applicances and motor items like refirgerators, furnaces, and washing machines. Of course power was out till they replaced it. I was told by the power company if we sustained a direct lightning stike nothing in our electrical system would have survived. That's why people use lightning rod systems.