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Lightning strike damage and grounding questions

New Poster

Lightning strike damage and grounding questions

I just moved in to a rented house here in Georgia two weeks ago. Last night we had a pretty bad thunderstorm and around 6PM I was sitting at my computer and we experienced a really close lightning strike. I can't find any obvious damage on the house and nearby trees that would indicate a direct hit, but it was a ears-ringing, house-shaking, everything-flashed white close hit. My computer and all electronics rebooted, but I remember hearing a distinctive metal "ping" (something like a BB hitting sheet metal) coming from my metal-enclosure router. Amazingly my computer works, and so does the Comcast cable modem, but my router (an Alix board in a metal enclosure), switch, and the onboard NIC on my desktop are all dead. My desktop doesn't even see the onboard NIC on the PCI bus anymore.


So I've ordered a PCIe NIC for my desktop and new switch and router. My (Comcast) modem still seems to be working fine.


I'm looking for input on what I can to do prevent this from happening again, and also some input on the current grounding of my CATV system (which as far as I can tell was done by Xfinity). Some pertinent details:


  • The house is in Georgia and was built in 1956. Most of the AC wiring appears original. The main panel is an ITE Imperial that I'd guess is probably from the '70s or so, and about half of the breakers are that old. According to my GB outlet tester, only three of 27 receptacles in the house are grounded. NONE of the GFCIs in bathrooms or kitchen are grounded. The house has been a rental for 20+ years, and appears to have been repaired as such - i.e. little money put into anything that doesn't photograph well.
  • The electrical service entry is at one side of the house and the cable service entry is at the other side. My desk with computer, modem, switch, etc. is up against the exterior wall with the CATV service entry; it's only about a dozen cable-feet from the CATV drop but some of the longest runs for mains power.
  • All of the electronic/network equipment in question is on the same APC surge protector. No damage to anything that wasn't connected to the switch, and no damage to some things that were (standalone AP, Raspberry Pi, etc.)
  • There's one cable box on the coax in addition to the modem, but it's on a *much* longer run. As far as I can tell it's unharmed.
  • The CATV aerial drop goes through a grounding block which is bonded (with relatively new-looking solid copper green-jacketed wire) to a terminal in the crawlspace under the house that also bonds the 2-way splitter and... another ground wire that goes off across the house towards the service panel. It's hanging loose, draped over some nails and the HVAC ducts, draped here and there, and finally connected to a really corroded and dirty piece of heavy copper wire disappearing between two floor joists in the direction of the mains panel. I have no way of knowing if that heavy (bare) copper is even connected to anything on the other end, or just hanging up in the wall. Given the coloring and level of dirt on the wire, it appears that all of the ground wiring from the CATV drop to this point was done at one time by Comcast.
  • The one thing in the house that has been upgraded is the water, which is all PEX including the service entry. So there's no metallic cold water piping to bond to. As far as I can tell, practically nothing in the house is bonded.
  • The bonding run from the CATV blocks to... wherever it ends... is about 40 feet, probably closer to 50 feet with the way it's just draped here and there.
  • There's no ground rod that I can find anywhere for the mains electical, either outside the house or in the crawlspace. I can't easily get the main panel open to check because it's recessed in the kitchen wall and has so many coats of paint that I can't even see the screw heads on the panel cover anymore.

My theory given the proximity of my desk/network HW to the CATV service drop, and that the only damage in the house is to equipment connected to the same router as the cable modem, is that the surge entered through the CATV line and somehow jumped to the ethernet cabling without harming the modem?


I'm a software developer and spent a few years doing datacenter and commercial networking and cabling, but this residential stuff is way different from that. I've also never had lightning-related damage before.


Does anyone have any thoughts on whether my theory of CATV lines as the surge entry point seems right, and whether the possibility of a bad (or nonexistent) ground for the CATV could contribute to the problem?


Lastly, any suggestions on how to protect my computer and the replacement router and switch? My current plan - which admittedly seems like overkill and maybe misplaced - is to move the cable modem off of the surge protector and to a different circuit in the house, and then connect the cable modem to my router with a pair of fiber media converters... so the cable modem has no conductive path to any of the other electronics, other than back through the mains wiring to the panel, and then to the circuit that the computer is on.


I know this has been a long post, but I've been researching for most of the last day and I'm really outside my area of knowledge here...

Valued Contributor

Re: Lightning strike damage and grounding questions

Well, you keep saying CATV wiring.. but I believe you mean COAX lines..
New Poster

Re: Lightning strike damage and grounding questions

Um... yes, Coax. Apologies if CATV is no longer an acceptable term... but yes, I'm aware that my "community" doesn't have its own "antenna".
Valued Contributor

Re: Lightning strike damage and grounding questions

Not sure what " your community not having an antenna " has to do with anything, at all. The coax line is the main wiring used from your drop line to your inside cabling inside your home, to your modem/tv boxes. Anyway, wasn't trying to be rude, but considering between your drop line and your modem and your computer network, BOTH of those types of wires are used, it makes it confusing. Yes, it is common for a coax line that is not properly grounded/not grounded at all, to be overloaded and fry equipment. Honestly, we could theorize all we want, but without actually having someone look at it, there is no way to be sure. Also, to prevent this from happening again, you need to have your house rewired. I doubt the landlord will pay for it though.

Re: Lightning strike damage and grounding questions

Hi @jantman,

I've seen lightning strikes do some funky stuff, just like you experienced. Some stuff survives, others not so much. You seem to have a pretty good understanding of bonding/grounding. The idea is to equalize the potential between the coax system and your home's electrical system. Even a properly bonded coax system won't protect you in the case of a lightning strike, that is not its purpose.  You want a 75 Ohm surge protector to guard against lightning strikes. With that said, a 40-50 foot ground wire off the block would not be up to code. If the system is not grounded/bonded correctly then Comcast may compensate you for your damaged equipment. It's their responsibility to install the ground properly. At the very least they can replace the old/corroded wiring. 


I've asked a Comcast employee to help you. You should expect a reply in this thread. 

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Official Employee

Re: Lightning strike damage and grounding questions

Hi @jantman


I can help by starting a damage claim. Can you please verify your first and last name, full street address, and the phone number or account number associated with your services in a private message? 


To send a private message click on my name "ComcastChe", then click private message me.

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Official Employees are from multiple teams within Comcast: CARE, Product, Leadership. We ask that you post publicly so people with similar questions may benefit from the conversation.
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