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Discussion Starter #1
I am just getting the destruction of another power surge cleaned up and wondering what others are doing in the line of prevention. June 4th at about 6 pm a surge ripped through 8-9 yards at last count doing thousands of damage at probably every one. There was a small thunderstorm that rolled through right about then but later the power company Fortis called and apologized for all the power outages and things going on. They are doing some major construction in the area. So not sure where the problem came from. Insurance deductible is $2,500 so it will be just over that to get everything running again and if I did make a claim I lose my claims free status for 6 years so will be paying back all I got and then some. My biggest damage was to my high efficiency condensing boiler combustion motor board and a couple of I Links. Relay panels for pumps. I have accumulated quite a stack of these components over 10 years. The old style boiler got hit, tripped the breaker, but all it needed was to turn the breaker back on. So I have been trying to educate myself (and all the local electricians) about the right way to do this. We live at the very end of a small power line. 14,400 V or maybe lower. We often get hit here. Way more often than neighbors on other lines. So I am leaning toward doing something a little more than average at suppression. From what I read, a "cascading system" is the best protection. That means I would have a large Type 1 MOV (metalic oxide varistor - which is two metal conductors precisely placed about .002 - .003" apart that a high voltage can jump and be bled off to ground) located close to the transformer pole to "grab" the big voltage surges that can be in the 10,000s of volts and 10,000s of amps. The second level would then be smaller and more precise Type 1 or Type 2 MOV units on each breaker panel where it enters a building. This cleans up the power even more to get down to the 117 - 122 volts that so much modern solid state controls require. As a third level in the cascade approach would be your power bar type surge suppressors on your computer, TV, etc. But what about all the other appliances and almost everything in your house and shop that has mini computers in them? Like a half dozen small maintenance battery chargers that are now dead. And these suppressors clean up voltage surges within your system that come from fridge, water pump, any motors in the shop etc.that shorten the life of all your electronics. So that's what I think I know. The more I read and talk, the more confused I become. There are dozens of companies making these things and each company has dozens of models with different technology, and different warranties for downline protection of your electronics.

So I found a smart electrician that has installed lots of these "systems" on large industrial complexes that use huge amounts of power for all kinds of things. And lots of computer based controls and monitoring. He said I should do the cascading method. In my travels I have heard about several customers installing small MOV units that are supposed to be adequate for the job, that have them blow out every time there is a surge and need replacing. If not every time, it seriously shortens their life to 2-3-4 hits. So I mentioned that I had found a very high capacity permanent suppressor designed for 347/600 V 3 phase WYE 4 wire plus ground. It is rated for up to 500 KW power supply and capable of suppressing 500,000 Amps of surge. There is no voltage rating but some of the small ones mention up to 6,000 volt spikes so this one is likely a lot more. This suppressor is a Surge Pure MACH 4 TVSS M4-1600-4 for primary locations. I will install this one just off the splitter panel that is close to my transformer pole. The second level of 4 suppressors I am looking at is Square D (now Schneider) SDSA1175 that can be mounted to a 20-30 amp breaker as close to the main as possible in the main panel of each building. This allows install and maintenance work without having to shut down the whole yard or building. So if the Surge Pure brings the voltage down to 600ish, then the 1175 can handle up to 700ish, we should be covered. Some of the larger suppressors can cost in the 5 figures range. I have found some of my parts on Ebay for just over $1,000. This smart electrician thought this was a very good approach to my problem and said I should go for it. He said no problem hooking the two 120 V hot legs to A and C and hook neutral to B on the big one. From some more reading I find that UL code in the US has made surge suppression a part of code as of 2014 I believe it was. Does anyone on this forum have any experience or suggestions? I was hoping Ken would weigh in!!
 

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Ouchy. When you say another when was the last one? Knock on wood we’ve never been hit. We have a large UPS that protects the major electronics in the house but a spike would still kill a lot of stuff. What isn’t loaded with a ecu nowadays.
What about some of these in each load center to clamp the nasty’s?
 

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Is your deductible 2500 straight across or 2500 to a certain dollar amount of damage then a percentage above that number. The fella who owns the maitnence company I contract to also farms with his brother, last fall they took a rock through the combine and he thought it was pay 2500 and get a rebuilt combine, it was 2500 to the first 10k of damage, then 25% of the total bill after that. So they paid a 25% of a 62000 bill. That same day a big outfit east of us took in 3 rocks and another guy took in a rock, there were 5 combines at Deere with rock ingestion that afternoon
 

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I have a whole home surge protector on my electrical panel. Will take one surge, then it has to be replaced. Electrician had put it in, was not that expensive.
Don't have one in my shop, should probably get that done as well.
 

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I can give you some theory TA but my experience is on the high voltage systems and haven't done any work on systems under 600v to address power quality problems. I have seen Eaton TVSS units showing up in 600v panel boards when commissioning but since this gear is relatively new I haven't seen failures or done testing/troubleshooting on them to need to learn how they work or how effective they are.

I think it is a good idea and is entirely dependent on the nature of your supply. If you live in the city and are one of 10,000 people fed off the same loop and everything is underground fed then you likely don't need much more than a powerbar with some surge protection. On a farm fed by a long overhead line which increases the odds of surge due to lightning you have reason to think about these things.

So the basics are a spark gap is old technology and was prone to explosion. I don't see them in high voltage systems anymore. It's all MOVs used to clip voltage spikes from lightning. But they do fail now and then but I haven't seen one explode, always identified by testing then getting a crane out to change out. It is up to the utility to put surge protection (call them MOVs or lightning arrestors - same thing) on their line, it's not your infrastructure so you don't have a say in that.

So you can only protect and install things on equipment you own so we are talking under 600v. And therefore I can only theorize on what would be needed since I have not done it personally.

To understand fault current and thus sizing, 35,000 amps is lots. The transformer the utility gives you is a resistor (correct term is impedance since TA is following those details) between the high voltage line and your service. If you take the transformer impedance which will be on the nameplate somewhere as "%z" you will be close. 5% z is close enough though, it maybe 3.5% of 6% but 5% is easy. 5 divides into 100 =20. If you have a transformer rated for 800 amps into your equipment then 800x 20 is 16,000 amps fault. Don't need surge protection that handles much more than that.

Now, let's look at the real issue and what you really need to understand. If 8 to 9 people suffer the same damage there is something to consider. I may be wrong but I will give some theory why I may be right. Usually a spike will find the weakest link and flash over thus clipping the spike. See my reference to spark gap previously - I am trying to form a mental picture. So, theoretically one customer should see a lot of damage while saving others. The person closest to the strike sees biggest spike as the surge travels down the line the line is essent a resistance to reduce it somewhat.

So what can effect 8 to 9 people is a theory to understand. When a voltage is shorted to ground you have high current. An electrical system is a big inductor meaning it resists a change in state. That short circuit creates a change in state but we know the current is there so the system has adapted (it could not resist) what happens is the voltage collapses (clipped to ground), the short circuit current flows (massive surge on system) but all the systems connected have adapted to this short circuit current and try to support it (inductor resist change and the new normal is high current) so all systems discharge into this short circuit.

So, the gist is > voltage clipped to ground =high current. Your system is now feeding its own stored energy into that short circuit trying to support the voltage. Current from your system feeding through the resistance that is your system is voltage (I x R = V). So your system discharging into the fault is creating a voltage spike in your system that is actually damaging your system. This is a reasonable explanation why many locations can see damage from one spike.

So a good system that removes spikes include a means to smooth the transition. A voltage going from peak to 0 in a vertical line is bad. This is how you get transients. A fast transition from one state to another creates its own spikes as the system tries to maintain a steady state. So you will have a capacitor to shape the slope of the clip to bring it down as a ramp versus a vertical collapse. The capacitor discharges into the short to help smooth it.

The smoothing component is what differentiates a simple device to clip the voltage (spark gap or MOV) from something that protects the system more so.
 

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Clarify a bit more what I just said rather than edit.

An example to visualize how things work, maybe later I can figure out how to fit into lightning protection.
Let's say you have a short circuit on your site. Fault current is flowing into that short and is passing through a fuse. The fuse does its thing and opens. A fuse is on or off, a breaker actually draws an arc and dissipates some energy while ramping down the current. A fuse is instant. So a fuse instantly stops the flow of current but your system is trying to maintain that new state of high current (inductor resists change) and so this energy suddenly interrupted is looking for a place to go. If power = V X I and we know high current is flowing into the short and that means power is there, then if you go to 0 current then V is trying to go to infinity to maintain the equation of P = V x I. So it is perhaps valid to consider that a capacitor used for smoothing voltage is there to absorb that current. The capacitor is at 0 Volts during the fault but the moment the current is interrupted and looking for somewhere to go, then it has a path into the capacitor.

The basic design theory is if you are installing devices to clip the voltage, it goes hand in hand with installing surge capacitors to smooth the voltage and reduce system spikes when a voltage is actually clipped. How I explain that in theory is a different matter.
 

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Discussion Starter #7
Ouchy. When you say another when was the last one? Knock on wood we’ve never been hit. We have a large UPS that protects the major electronics in the house but a spike would still kill a lot of stuff. What isn’t loaded with a ecu nowadays.
What about some of these in each load center to clamp the nasty’s?
Thanks Joe. Yes OUCH! We have had dozens of damaging hits over the years and my electrician (s) have talked about installing a surge suppressor for the whole house/yard but always seemed hesitant so it never got done. As a count of hits I can count the growing pile of boiler parts that in 10 years is now at 4 blown I Links, 2 blown combustion motors, numerous thermostats, and various microwave clocks, cooking range clocks, clock radios, battery chargers, etc. etc.I can relate sitting in the kitchen and seeing a flash of electricity and a shower of sparks shoot all the way across the kitchen before. This is why I started this post because I was wondering if everyone has this much trouble. Apparently from this thread lots of people have surge suppressors. And they are somewhat effective. Maybe one time protection and then how do you know if your suppressor is good or not? Most of the ones I am looking at, like the Square D SDSA1175, has LED lights to indicate if it is still good or if it is time to replace it. This 1175 is rated higher( 25kA short circuit current rating) than the BR Surge you linked which is 10kA. So does a higher rating make it better as in able to take a bigger hit? Or worse as in not sensitive enough??? This seems to be where the cascade theory comes into play where you install a larger suppressor outside at the source of power and a smaller one on each panel. The effective sizing of these things is what I am trying to establish. Is bigger better??? When it comes to lightning type strike they can be millions of volts AND amps. Seems to me the suppressor outside needs to be BIG. This is why I am thinking the Surge Pure MACH 4 1600 which has 560kAmp rating at 1000 Volts L-N would be able to take the big spikes and not blow up in one hit.
 

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Discussion Starter #8
I can give you some theory TA but my experience is on the high voltage systems and haven't done any work on systems under 600v to address power quality problems. I have seen Eaton TVSS units showing up in 600v panel boards when commissioning but since this gear is relatively new I haven't seen failures or done testing/troubleshooting on them to need to learn how they work or how effective they are.

I think it is a good idea and is entirely dependent on the nature of your supply. If you live in the city and are one of 10,000 people fed off the same loop and everything is underground fed then you likely don't need much more than a powerbar with some surge protection. On a farm fed by a long overhead line which increases the odds of surge due to lightning you have reason to think about these things.

So the basics are a spark gap is old technology and was prone to explosion. I don't see them in high voltage systems anymore. It's all MOVs used to clip voltage spikes from lightning. But they do fail now and then but I haven't seen one explode, always identified by testing then getting a crane out to change out. It is up to the utility to put surge protection (call them MOVs or lightning arrestors - same thing) on their line, it's not your infrastructure so you don't have a say in that.

So you can only protect and install things on equipment you own so we are talking under 600v. And therefore I can only theorize on what would be needed since I have not done it personally.

To understand fault current and thus sizing, 35,000 amps is lots. The transformer the utility gives you is a resistor (correct term is impedance since TA is following those details) between the high voltage line and your service. If you take the transformer impedance which will be on the nameplate somewhere as "%z" you will be close. 5% z is close enough though, it maybe 3.5% of 6% but 5% is easy. 5 divides into 100 =20. If you have a transformer rated for 800 amps into your equipment then 800x 20 is 16,000 amps fault. Don't need surge protection that handles much more than that.

Now, let's look at the real issue and what you really need to understand. If 8 to 9 people suffer the same damage there is something to consider. I may be wrong but I will give some theory why I may be right. Usually a spike will find the weakest link and flash over thus clipping the spike. See my reference to spark gap previously - I am trying to form a mental picture. So, theoretically one customer should see a lot of damage while saving others. The person closest to the strike sees biggest spike as the surge travels down the line the line is essent a resistance to reduce it somewhat.

So what can effect 8 to 9 people is a theory to understand. When a voltage is shorted to ground you have high current. An electrical system is a big inductor meaning it resists a change in state. That short circuit creates a change in state but we know the current is there so the system has adapted (it could not resist) what happens is the voltage collapses (clipped to ground), the short circuit current flows (massive surge on system) but all the systems connected have adapted to this short circuit current and try to support it (inductor resist change and the new normal is high current) so all systems discharge into this short circuit.

So, the gist is > voltage clipped to ground =high current. Your system is now feeding its own stored energy into that short circuit trying to support the voltage. Current from your system feeding through the resistance that is your system is voltage (I x R = V). So your system discharging into the fault is creating a voltage spike in your system that is actually damaging your system. This is a reasonable explanation why many locations can see damage from one spike.

So a good system that removes spikes include a means to smooth the transition. A voltage going from peak to 0 in a vertical line is bad. This is how you get transients. A fast transition from one state to another creates its own spikes as the system tries to maintain a steady state. So you will have a capacitor to shape the slope of the clip to bring it down as a ramp versus a vertical collapse. The capacitor discharges into the short to help smooth it.

The smoothing component is what differentiates a simple device to clip the voltage (spark gap or MOV) from something that protects the system more so.
Thanks for the detailed explanation Ken. I have to admit some of that is a little murky! LOL! I understand that below 600 V is out of your area of knowledge somewhat but I will ask you some specific questions and respect your answer as "opinion" since it comes from a much more comprehensive understanding than I have.

1/ Assuming I put a Sq D SDSA1175 on each panel which protects each of 4 branches coming from my 25 KVA transformer pole and splitter, will the Surge Pure MACH 4 1600-4 provide first line protection as a Type 1 MOV to "grab" bigger spikes and surges coming into my system? I realize the Mach 4 is 600 V 3 phase but it is rated for very large spikes which it seems that I am prone to getting. I have no depth of comparison of these specs but this Mach 4 is rated as 45,000 Amps of non degrading surge capacity, so it should be able to handle the 35,000 amps you mention as enough and do it over and over as time goes on without breaking down and becoming ineffective like all these other smaller suppressors. The only downside is cost of the Mach 4 but I found it at a great price on ebay.

2/ The Mach 4 1600 has a VPR (voltage protection rating) of 1200/1800 @ 20kA L-N/L-L . It also has a Max Clamping Voltage L-L of 1800 V and L-N of 1120 V. Will this provide protection ahead of the 1175 which has a VPR of 700 V L-N and a L-L V of 1200. Is that too big of a spread? There are other brands like an Intermatic IG2200 that has VPR of 800 and 1500V
 

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Discussion Starter #9
Is your deductible 2500 straight across or 2500 to a certain dollar amount of damage then a percentage above that number. The fella who owns the maitnence company I contract to also farms with his brother, last fall they took a rock through the combine and he thought it was pay 2500 and get a rebuilt combine, it was 2500 to the first 10k of damage, then 25% of the total bill after that. So they paid a 25% of a 62000 bill. That same day a big outfit east of us took in 3 rocks and another guy took in a rock, there were 5 combines at Deere with rock ingestion that afternoon
I believe from talking to an agent of Wawanesa that they pay everything over $2,500. I got bogged down in legal gobbledy gook after about page 15 of the policy so really have no good feel of what it really says. If they want to screw you they will find a loop hole. The loss of "claims free" status just gives them an opening to raise your premiums even more so I don't want to open that door.
 

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Thanks Joe. Yes OUCH! We have had dozens of damaging hits over the years and my electrician (s) have talked about installing a surge suppressor for the whole house/yard but always seemed hesitant so it never got done. As a count of hits I can count the growing pile of boiler parts that in 10 years is now at 4 blown I Links, 2 blown combustion motors, numerous thermostats, and various microwave clocks, cooking range clocks, clock radios, battery chargers, etc. etc.I can relate sitting in the kitchen and seeing a flash of electricity and a shower of sparks shoot all the way across the kitchen before. This is why I started this post because I was wondering if everyone has this much trouble. Apparently from this thread lots of people have surge suppressors. And they are somewhat effective. Maybe one time protection and then how do you know if your suppressor is good or not? Most of the ones I am looking at, like the Square D SDSA1175, has LED lights to indicate if it is still good or if it is time to replace it. This 1175 is rated higher( 25kA short circuit current rating) than the BR Surge you linked which is 10kA. So does a higher rating make it better as in able to take a bigger hit? Or worse as in not sensitive enough??? This seems to be where the cascade theory comes into play where you install a larger suppressor outside at the source of power and a smaller one on each panel. The effective sizing of these things is what I am trying to establish. Is bigger better??? When it comes to lightning type strike they can be millions of volts AND amps. Seems to me the suppressor outside needs to be BIG. This is why I am thinking the Surge Pure MACH 4 1600 which has 560kAmp rating at 1000 Volts L-N would be able to take the big spikes and not blow up in one hit.


I don’t know if I’d read a bunch into the current rating. They rate it a microsecond so somewhat glorified.

IMO the sacrificial type that goes right in a panel slot across each leg to ground is a pretty good start.

The sparks flying across the kitchen has me wondering just how hard your getting hit though.
 

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Discussion Starter #12
I don’t know if I’d read a bunch into the current rating. They rate it a microsecond so somewhat glorified.

IMO the sacrificial type that goes right in a panel slot across each leg to ground is a pretty good start.

The sparks flying across the kitchen has me wondering just how hard your getting hit though.
That's why I am looking at some of the bigger capacity suppressors as the first level of a multi tiered suppressor system. If we are getting lightning kind of voltage and amperage, the little ones that plug into a panel aren't going cut it. Was just talking to a neighbor in a different direction and on a different leg of the supply and two more farms hit there. The wall is all black above a power bar surge suppressor at his place.
 

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I would say you are on the right track TA. I looked at my house panel and I have a unit in there like Joe mentioned and has a status light for each leg with one light out so I guess I have to do something. Light out means failed so then I had a surge at one time that was too large for it.

I did some reading today to get a bit more informed. The cascade approach makes sense. You certainly want to protect the main incoming first, everything after that is optional. So it would make sense to put a large unit at the main service and smaller units at other panels to get those lower energy surges that are let through by the main one. And if the main unit takes a nasty hit and fails then the your other panels have some protection because a spike will no doubt be coming to them.

I didn't understand how these MOVs are being used in smaller systems. I always considered them as a fine tuned spark gap meaning they had better control of when they break over and short to ground. They can hold the current at a steady state for a short period of time where as a spark gap just flashes over and shoots all current to ground and so not controlled at all. So MOVs have a power rating and a short circuit current rating. The way I understand these low voltage ones is they are designing some of the MOVs to absorb more energy. So, rather than act as a controlled arc gap to ground with a small amount of resistance, they are increasing the resistance of the MOV thus reducing current to ground. So, if you can follow what I said earlier, reducing the current will reduce transient voltage spikes as a system tries to maintain a high level of short circuit current. So the energy rating of the surge supressor becomes a key point. I see KJ (killo joules) used often but have no idea how to transpose that to my background. But, it stands to reason that a supressor that can absorb more energy will reduce the magnitude of spikes travelling your system.

I looked at the two items you mention and the Mach 4 makes sense. Just clip the voltage and don't worry about absorbing the energy because you have other devices downstream and the rest of the system to act as an absorber. In my case, I have a house panel and a shop panel off the same transformer so I may benefit more from two of the same units but each one built with a higher energy absorbing rating than the one failed in my panel right now.

Keep in mind those voltage ratings are peak. A 600v system has a peak to peak voltage of 850v at normal operation and 490v to ground. That 1200/1800 seems a little high but there are codes and standards that I am not aware of so that may be perfectly fine. My thinking would be 50% of normal so perhaps 800/1400v but strange things happen when you send one phase to ground because the other two phases rise up in voltage (I would have to sketch to explain) so their numbers may be correct, it's maybe simply a matter of how they calculate and present the data. I would need to study more to know. But let's say that Mach 4 does let a spike through that is under its rating, then I think you are ok with the Square D as it will clip that spike.

Interesting stuff. Our farm has never had issues like you mention. Probably why I haven't looked into these things. But I may need to now.
 

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I don't know for sure, but the surge current rating may be how they define the energy rating. You really won't find a house panel that has higher than 18ka or 25 ka rated breakers because fault currents just are not that high for residential stuff. So a 80 ka surge current rating seems pointless. I suspect this is a simple way of defining how much energy the MOV can handle. 80 ka in milli second is more power than 35 ka in a milli second. Rather than use joules.
 

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Is your deductible 2500 straight across or 2500 to a certain dollar amount of damage then a percentage above that number. The fella who owns the maitnence company I contract to also farms with his brother, last fall they took a rock through the combine and he thought it was pay 2500 and get a rebuilt combine, it was 2500 to the first 10k of damage, then 25% of the total bill after that. So they paid a 25% of a 62000 bill. That same day a big outfit east of us took in 3 rocks and another guy took in a rock, there were 5 combines at Deere with rock ingestion that afternoon
I don't know where you guys are but, but in MB, Hydro has sometimes paid for damaged electronics. Not sure if it's only from faulty equipment failures. You still have the hassle of fixing tho.
 

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Discussion Starter #16
Thanks for all the input everyone. Yes I follow you Ken when you say adding resistance slows the drain of amps which reduces the voltage spike. I try to visualize electricity as liquid flowing in a pipe. If the flow stops instantly you see the hose or pipe jump from the pressure shock from inertia of the moving fluid. Electricity is similar I believe. An accumulator in the liquid system absorbs the shock much like you are saying to restrict the current discharge by restricting the flow. Am I hearing you thinking a capacitor would work like an accumulator? I am unsure of what will happen to the 120/240 1175 MOV when the voltage that the Mach 4 passes through hits it. My reason for trying to go a step better than a simple recommendation for a house is because of the number of serious hits we have. Half a dozen breakers were tripped in the last surge. I am not sure if that is high Volts or Amps. Likely both. From what I hear from the ordinary by the book guys is lots of people have a box full of burned out small house sized MOV surge suppressors in the corner of the garage. I am hoping the Mach 4 will grab the big voltage that may be in the 10,000 or 100,000 Volt range or possibly much more from a lightning strike. Too much for a normal house MOV to handle. This Mach 4 is supposed to be permanent so hopefully this combo will be low maintenance.

I am sure you know this but to get Joules you multiply watts X time in seconds. A 1 watt device consumes 1 Joule of energy every second. So joules brings time into the quantification of energy.
1 watt in 1 second = 1 Joule
30,000 watts in 1/10 second = 3000 Joules, the size of my power bar surge suppressor for $28.
My mind is getting ahead of the knowledge here, but if one of those 30,000 amp surges at 1000 volts hit for 1/10th of a second or 100 milliseconds would that be 3,000,000 Joules? I think I just fried my 3,000 Joule surge bar!!

Interesting trying to figure this all out!
 

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I don't know where you guys are but, but in MB, Hydro has sometimes paid for damaged electronics. Not sure if it's only from faulty equipment failures. You still have the hassle of fixing tho.
That is a good thought and they haven't said no yet. But I am holding off trying to collect as much info as I can so they can't snow us with some line. They have left two long messages apologizing for the power outages and surges that have been happening recently. So admitting to a problem. But the most recent, today, they were unsure but maybe it was a bird strike on a transformer and they were going to look into putting up bird deflectors. No mention of "send in your bills". I am south east of Edmonton. And I just learned of 4 more farms and town people with substantial damage from this electrical problem. I do know that Fortis is doing some line construction or repair in the area so maybe they don't have all their usual surge suppression equipment in place. So who should pay then???
 

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It's rare in Sask but have seen some powerlines in Manitoba where a higher voltage line is strung on same poles as lower voltage. Say 72 KV on top and 25 KV below. If a 72 KV conductor falls down for some reason and hits the 25 KV line, you get lots of damage and it is occurring for longer than a one shot lightning strike.

The water hammer analogy and accumulator is a great way to visualize. A surge capacitor acting like an accumulator makes sense but I never tried to correlate the two before. Surge caps and spark gap arrestors were used together a long time ago. Now we don't see surge caps much except for at terminals of motors. Probably because MOVs have become standard and now the electrical system can act more like an accumulator without as great a risk to damage from transient voltage spikes (water hammer analogy).

I would stick with the manufacturer design values. If you are installing on a 120/240v system then go with what they design for the system. You could talk to them directly about your issues and your thinking TA. You understand the basics well enough to explain your thought process and then let some who really knows these things to confirm what makes the most sense.

I was rethinking my early post regarding short circuit current. From a design/analysis standpoint, what i said was based on nameplate operating voltage. When you have a short on the system and fault current flows, the voltage is actually collapsing. With a lightning strike the voltage is actually going higher. So, if I said a system operating at normal voltage has a maximum theoretical fault current of 25 ka, then i need to rethink this and say that if the voltage is doubled before being clipped by a surge protector, then the fault current may be 50 ka (just throwing a number out there as I have no idea the methodology to calculate for voltage surges).

And so we can get to joules. What I meant is, nothing in my design back ground involved joules - never used that unit of energy to calculate anything electrical before. But from a surge suppression perspective I think it seems valid. And I think why I have a light burnt out on the suppressor in my panel. And that comes back to my thinking that a guy with a house in the city with all underground feeds can get by with a smaller rated surge suppressor than us on farms with an overhead powerline exposed directly to lightning strikes. Think of a city power grid as an accumulator if there ever was a surge (say utility power transformer shorts from high voltage side to low voltage side) vs you with the only power network at the end of a 15 mile overhead line. Two very, very different exposures to voltage surges.

So probably a good time to talk to a manufacturer directly since this is quite a bit out of my wheelhouse. But, if I understand your system with a main panel that then feeds to sub panels ( a series system where as I have 2 panels in parallel off the transformer) then I would take your approach as a starting point to discuss with a manufacturer who knows all aspects of such design needs.
 
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