Recently had a strong thunderstorm roll through and strike very close if not strike the house. One the second floor of the duplex(seperate panelboard) one afci protected circuit was blown and on the first floor, the external cable modem was damaged, the cord for the modem was plugged into a surge protector strip and nothing else on the strip was damaged. Any ideas on what may have caused this?
Lightning strike
- Thread starter bwyllie
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Re: Lightning strike
More than likely you took a hit on the phone line and it discharge via you modem, quite common. Couple of things you can check.
1. Look at your NID (Network Interface Device, the box outside your house where the telephone company terminates their lint too called the demarcation point) and look to make sure the protectors inside are properyly bonded to the electrical service ground electrode.
2. Make sure the protectors inside the NID are functional.
3. Use a surge arresstor on your PC that also has an arrestor for the phone line, and telephone wire is not shielded.
[ May 28, 2003, 11:27 PM: Message edited by: dereckbc ]
More than likely you took a hit on the phone line and it discharge via you modem, quite common. Couple of things you can check.
1. Look at your NID (Network Interface Device, the box outside your house where the telephone company terminates their lint too called the demarcation point) and look to make sure the protectors inside are properyly bonded to the electrical service ground electrode.
2. Make sure the protectors inside the NID are functional.
3. Use a surge arresstor on your PC that also has an arrestor for the phone line, and telephone wire is not shielded.
[ May 28, 2003, 11:27 PM: Message edited by: dereckbc ]
Re: Lightning strike
No difference in technique than with a phone line modem, and more prone to problems due to ground being involved. I'll take a few shots in the dark.
Look at the demarcation point of the CATV. There should be a device installed at the demarcation point called a ground clamp with a built-in surge arrestor. It looks like a coax splice connector with a ground screw terminal. This device should have a dedicated ground wire going to the AC service GEC. They are notorious for using mechanical clamp connectors, which come loose almost immediately. If it is missing or improperly installed you likely found the problem
Another common problem is the CATV companies often install their own ground rod without bonding it to the AC service ground electrode, or do not ground the coax at all. This is sure to cause problems.
I suggest you read up on NEC 820.40 and understand the minimum requirements, then inspect the CATV. If you do find the ground clamp installed try to determine if it has built-in surge protection. If not replace the unit with one that does.
The other suggestion I can give you is to find a quality surge suppressor to use on the PC itself. Look for a unit that has a built in coax surge suppressor to supplement the one outside. It will form a ground reference equalizer at the device and help prevent this from happening again.
But be aware that surge suppressors installed on PC's are only a class A devices, if even that, and will not likely prevent any damage on a direct strike to the AC line. It would take a class C device installed on the main service panel to afford any real protection. The class A devices installed on PC's are just a backup or supplemental device, and most of them offered on the market are junk.
[ May 29, 2003, 04:21 PM: Message edited by: dereckbc ]
No difference in technique than with a phone line modem, and more prone to problems due to ground being involved. I'll take a few shots in the dark.
Look at the demarcation point of the CATV. There should be a device installed at the demarcation point called a ground clamp with a built-in surge arrestor. It looks like a coax splice connector with a ground screw terminal. This device should have a dedicated ground wire going to the AC service GEC. They are notorious for using mechanical clamp connectors, which come loose almost immediately. If it is missing or improperly installed you likely found the problem
Another common problem is the CATV companies often install their own ground rod without bonding it to the AC service ground electrode, or do not ground the coax at all. This is sure to cause problems.
I suggest you read up on NEC 820.40 and understand the minimum requirements, then inspect the CATV. If you do find the ground clamp installed try to determine if it has built-in surge protection. If not replace the unit with one that does.
The other suggestion I can give you is to find a quality surge suppressor to use on the PC itself. Look for a unit that has a built in coax surge suppressor to supplement the one outside. It will form a ground reference equalizer at the device and help prevent this from happening again.
But be aware that surge suppressors installed on PC's are only a class A devices, if even that, and will not likely prevent any damage on a direct strike to the AC line. It would take a class C device installed on the main service panel to afford any real protection. The class A devices installed on PC's are just a backup or supplemental device, and most of them offered on the market are junk.
[ May 29, 2003, 04:21 PM: Message edited by: dereckbc ]
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