I'm not trying to start a flame war, I am just trying to provide information to prevent bad stuff from happening.
Most likely the surge came in from the mains and left through the phone line, using your modem as an exit port. Consider that a MOV's are typically wired to divert energy to ground wire, and that the phone line is also connected to the ground wire. There is a ground loop to the POTS line. The surge diverted to ground back into the modem to fry it. Was it just your modem fried or were all your phone line devices fried too? I am betting it was just your modem, If lightning hit your phone line, you can bet everything else connected to POTS lines (include other POTs lines connected to your building) will also get fried.
Another words, what appears to be a surge on the phone line, because the modem blew often is a false diagnosis of the problem. Your modem died because of MOVs diverting energy to the ground wire, creating a very high voltage differential between ground and the POTs line connected to your PC. MOVs don't absorb energy they divert it.
Frequently asked questions about surge protectors / suppressors for the home
Fuses are way too slow. They take 100's of milliseconds to 10's of seconds to blow. a high voltage spike can cause damage to electronics in nanoseconds. Short nano-second spikes are rare, but all it takes is one to ruin your week\month\year\etc (depending on how much damage is done). Also very high current surges will vaporize the fuse filments into plasma that will provide a low impediance path for current to flow, well after the fuse has blown.
Most of the time the line transformer suppresses or chokes most of the energy, then every now and than a tree (or drunk driver) will knock the transformer from pole, disconnecting a the center tap ground and causing a large common mode surge (as happened to me).
How much protection depends on how much risk you wish to take. I prefer to have the highest level of protection on my most expensive equipment for those 1 in 1000 surges. I don't like the idea of diverting a surge to the ground line, only to attack other devices from their ground connections. Its like moving a flaming cart away from one building and placing it next to another. You saved one building, but lost another to the fire. Surpressing the surge using a cap bank is a better solution (like pouring water on to the flames).
That doesn't mean they are not degraded. a MOV consists of thousands to hundreds of thousand micro pathways for current to flow during a surge. Each time a surge happens a few to thousands will blow reducing the amount of current it can carry. eventually it will lose its ability to pass any significant current. a resistance test on a MOV does not tell you how much current it can pass during the next spike. All it tells you is that the device isn't completely blown.
Metal Oxide Varistor Degradation | IAEI Magazine Online
Please read Pages 3 and 4:
http://www.wago.us/downloads/Transient_Surge_Technologies.pdf
Most likely the surge came in from the mains and left through the phone line, using your modem as an exit port. Consider that a MOV's are typically wired to divert energy to ground wire, and that the phone line is also connected to the ground wire. There is a ground loop to the POTS line. The surge diverted to ground back into the modem to fry it. Was it just your modem fried or were all your phone line devices fried too? I am betting it was just your modem, If lightning hit your phone line, you can bet everything else connected to POTS lines (include other POTs lines connected to your building) will also get fried.
Another words, what appears to be a surge on the phone line, because the modem blew often is a false diagnosis of the problem. Your modem died because of MOVs diverting energy to the ground wire, creating a very high voltage differential between ground and the POTs line connected to your PC. MOVs don't absorb energy they divert it.
Frequently asked questions about surge protectors / suppressors for the home
Fuses are way too slow. They take 100's of milliseconds to 10's of seconds to blow. a high voltage spike can cause damage to electronics in nanoseconds. Short nano-second spikes are rare, but all it takes is one to ruin your week\month\year\etc (depending on how much damage is done). Also very high current surges will vaporize the fuse filments into plasma that will provide a low impediance path for current to flow, well after the fuse has blown.
Most of the time the line transformer suppresses or chokes most of the energy, then every now and than a tree (or drunk driver) will knock the transformer from pole, disconnecting a the center tap ground and causing a large common mode surge (as happened to me).
How much protection depends on how much risk you wish to take. I prefer to have the highest level of protection on my most expensive equipment for those 1 in 1000 surges. I don't like the idea of diverting a surge to the ground line, only to attack other devices from their ground connections. Its like moving a flaming cart away from one building and placing it next to another. You saved one building, but lost another to the fire. Surpressing the surge using a cap bank is a better solution (like pouring water on to the flames).
That doesn't mean they are not degraded. a MOV consists of thousands to hundreds of thousand micro pathways for current to flow during a surge. Each time a surge happens a few to thousands will blow reducing the amount of current it can carry. eventually it will lose its ability to pass any significant current. a resistance test on a MOV does not tell you how much current it can pass during the next spike. All it tells you is that the device isn't completely blown.
Metal Oxide Varistor Degradation | IAEI Magazine Online
Please read Pages 3 and 4:
http://www.wago.us/downloads/Transient_Surge_Technologies.pdf
My job is largely in hospitals. I hear a lot of complaints about the quality of the utility power. One hospital had many of their variable speed motor drives trip off line at 7:00 am daily. I called my friend a power engineer at the utility, he told me that at 7:00 am they switch in large capacitor banks to adjust the power factor, “no big deal” the spike is well within Public Utility Commission quality standards. And oh by the way all those motors and ones like them is the reason for the capacitor banks being switched on line. Same hospital has a power / electronics intensive cardiac cauterization lab that was experiencing power issues and some items were tripping off line during procedures. Several hundred thousand dollars later the lab had new isolation transformer power conditioner. A generator power conditioner was too expensive. Turns out the switching power supplies in some of the lab equipment was causing the issues in the other sensitive to power quality equipment. Hospitals are full of “K” rated transformers to isolate stuff from other stuff. Separate “clean” grounds run all over the place. If you want to see power conditioners look in an operating room.
Is your stuff innocent?
DT
All just for fun!
Is your stuff innocent?
DT
All just for fun!
to be honest, i do not know....these chokes were taken from discarded mainframe computer psu's...i just gave those orphaned parts a new application.
Hello all,
Do not remove the ground clamp and bonding conductor from the iron gas pipe, it is required to be there.
We are speaking of the grounding of your electrical service and bonding of conductive systems in the building. The “ground” can be a water pipe, a grounding grid, a Ufer or a driven rod. Next the structural steel frame, metallic water piping and gas piping are all required to be bonded together to maintain a common potential. Think of it this way, you do not want to become the bonding jumper between the kitchen faucet and the gas range.
The reference for not using the underground gas piping for a ground is correct. Underground gas piping is technically not in the building and is required to be electrically isolated from building piping with a dielectric isolation fitting or flanges.
If you want Code references it will need to be later. My copy of the NFPA 70, NEC, California Electrical Code are at my desk at the office.
DT
All just for fun!
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Enhanced Main Voltage at Output from Power Conditioner
A user tell me, that the outut voltage from his power conditioner (in use some years ago) was 10% above from that one at the wall (i. e. 250-260VAC instead 225-235V).
Thus he observed extremly reduces lifetime of the used vacuum tubes.
He don't recall the model number (maybe "NF3-2000W"), but the brand name he know yet exactly: Mudra Acoustics by Nexus Acoustics - go to
Nexus Acoustics - Mudra Akustik
Are there similar experiences observed by the use of this brand?
Thank you for comments.
A user tell me, that the outut voltage from his power conditioner (in use some years ago) was 10% above from that one at the wall (i. e. 250-260VAC instead 225-235V).
Thus he observed extremly reduces lifetime of the used vacuum tubes.
He don't recall the model number (maybe "NF3-2000W"), but the brand name he know yet exactly: Mudra Acoustics by Nexus Acoustics - go to
Nexus Acoustics - Mudra Akustik
Are there similar experiences observed by the use of this brand?
Thank you for comments.
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