I found out a few months ago that cable TV/Internet service is supposed to be grounded at the entrance to the building. I learned the hard way, when during two storms, the Comcast Business cable at my office was hit by surges (I suppose from lightning strikes somewhere exposed upstream). The surges killed our cable modem, which Comcast had to send a technician out to replace and reconfigure each time. That part cost us a day or so of downtime in each storm. Worse, the surges traveled down the Ethernet cable from the modem and destroyed other equipment. The first storm fried one Ethernet port in our firewall appliance, and the second strike killed all the Ethernet ports in our firewall appliance and a packet shaper rate limiter attached to it, equipment worth around $8,000 which we had to replace and make an insurance claim for.
After that, I did some research about what could be done. It appears that the National Electrical Code requires communications cable lines to be grounded at the building service entrance, as referenced in this Q&A from the New York State government and this Q&A from the Electrical Contractor Network. I am not an expert in the topic.
I came up with a two-pronged defense. The first was, we had Comcast send another technician out to ground the cable to an electrical panel where it enters our server room. He affirmed what I had read on the net, that the cable is supposed to be grounded at the building service entrance. He said that Comcast used to do it by driving a rod in the earth, but that now grounding to an electrical panel is preferred. He demonstrated the constant voltage differential between the two by touching the grounding wire against the splitter lug while the other end was screwed to the breaker panel; we saw little sparks arc.
The second prong of defense was to install an Ethernet surge protector on the CAT5 run between the cable modem and the new firewall, so even if a surge did hit the cable modem, it wouldn’t continue up the line to damage other equipment. We got the APC PNET1GB ProtectNet Standalone Surge Protector for 10/100/1000 Base – T Ethernet Lines for around $24 from Amazon. It uses a grounding wire run to an electrical outlet’s screw.
After getting the office taken care of, I implemented the same measures at home. We happen to have a Comcast-provided splitter where the cable enters our house, with a grounding lug on it, and a corner clamp for grounding already installed on the electrical meter box just above it. So all I needed to do was run a copper wire between them. I also got the Ethernet surge protector noted above to run between our cable modem and firewall/router.
So far, so good; no damage during storms at either place. It’s sad that Comcast doesn’t consistently protect customer lines when they do an install, though. If you have a cable line that isn’t grounded, consider calling your cable provider and asking them to send someone out to do it, and/or install an Ethernet surge protector yourself.
Here are some pictures of the installation at home.