Many homeowners and apartment dwellers discover too late that their lovely surge strips were completely useless at protecting their computer and hifi gear from lightning when a surge has come in through a cable TV/Internet or antenna.
Whats worse is that minor surges that don't cause visible, or olfactory evidence can still make your TV, PC or music streamer useless from damage to a $1 network part.
Surge protection for your household outlets is critical but if that's all you do you are still vulnerable to surges from your Internet and Ethernet wiring. We'll show you how to close these gaps.
Full Disclosure
Doing the research for this blog takes time and effort and I justify it by using Amazon associate links. Purchasing items linked on this page will probably make me a buck or two. It is also true I personally use all off the approaches and most of the gear I link to.
When you consider how much time and effort to take in protecting your
home consider not just the cost to replace but the time and effort to
replace, and whether you can live without the gear while fixing it. My
work PC and home office equipment for instance is not at all something I
want to think about replacing. My stereo receiver is 60 lbs and an
absolute beast to take out of the rack, anything I can do to keep it
from moving before I die is well worth it. On the other hand, I have lived in
the south near thunderstorm prone areas for about half of my life so the
risk assessment for me may look more paranoid than for you.
Perfect Protection
There's no such thing as perfect protection when it comes to lightning, or a car accident, but just like a like car accident our goal is to turn the majority of incidents into survivable events your gear metaphorically walks away from unscratched. A better example may be a bicycle helmet. A 5 MPH accident on a bicycle can cause lethal head trauma, but a helmet transforms most of them into situations where you brush yourself off, fix the chain and keep going.
Network Surge Damage
Any copper wire that crosses the barrier from outside your home to inside can be a source of an electrical surge entering your home. Electricity doesn't much know the difference between an Ethernet cable, copper pipe or your household wiring so once inside it will look for the easiest way to reach the earth. This can be through network ports or a combination of network ports and AC wiring. It's not uncommon for lightning to find multiple paths to ground either.
We are going to divvy up the areas we are concerned with into three zones:
- The external outdoor/indoor interface
- The cable modem
- Indoor Ethernet wiring
Our working principle is to isolate and minimize potential damage caused by a surge attempting to find a path to ground via your home and electronic equipment.
The Outdoor/Indoor Interface
When we think about how the Internet reaches our home there are several kinds of Internet service providers:
Even homes with fiber service may have fiber terminated outside, with coaxial or Ethernet bridging the gap. What we really care about is the cable, if any, used through from outside the home to inside.
Non Metallic Internet
If you have 5G or fiber optic cable coming through the wall you can skip this section and go onto the cable modem and indoor wiring sections. 5G and fiber cables are immune to surges.
Coaxial Connections
Outside of the home you want to
use a gas discharge coax surge protector. This is actually true for all your coax wires, including antennas on the roof, satellite dishes in the yard, etc. These devices are imperfect, their job is to minimize the blast radius and also direct high surge currents to your ground rod OUTSIDE your home. Mount it directly on the
ground block outside, which is required by law for all coax cables coming in.
To be clear, a ground block is required by electrical code (i.e. the NEC) to ensure your home's ground (and by extension the neutral) wires are at the same potential as the coax cable shield and prevent one type of dangerous situation but they are not surge or lightning protectors of any sort. In particular it offers no protection against a high voltage being present on the inner conductor.
Coaxial surge protectors are not required, but allowed and IMHO necessary and the best place for them is on the outside grounding block.
The Details
GDT discharge protectors are self-healing and high current. The bad part is that they may not respond as fast as other devices with diodes or MOVs. The tubes inside will energize around 90V but because it may take a few picoseconds to activate you may end up with 800V-1000V inside for moments. This will prevent the large amounts of surge current but that may be enough time to fry sensitive integrated circuits in the modem.
The reason I'm so fond of pure GDT protectors outside despite this vulnerability is they rarely need to be replaced and can handle high currents safely. If I'm going to have a 100A surge I want it to happen outside my home, not inside via the cable hidden in my walls.
My personal experience was that when I first moved in I put a GDT outside and wired my modem to my wifi router with Ethernet. We had a major storm in 2021 that took out the cable TV provider's equipment and every cable modem in my subdivision. However in my home that's all it did. The cable modem stopped working, but with no visible damage and no smell and my Wifi router worked perfectly. Of all my neighbors I'm the only one with any Ethernet cables at all inside and I suffered no damage at all indoors.
Ethernet
If your fiber provider uses an Ethernet jack outside as the interface into your home I suggest an
Ethernet isolator, not a surge protector like this one. Absolutely avoid Ethernet "surge protectors" with ground pig tails. What matters here is the cable length. If it's 2' from outside to the cable modem you can skip this. If it's 20' you really should isolate.
The Cable Modem
If you are an apartment I can pretty much guarantee your apartment complex does not have adequate lightning protection for the network distribution. You may not be able to mount a coax surge protector on a ground block but it's not a bad idea to have one anyway attached to the modem.
If you have optical fiber coming in there's nothing you need to do, they are inherently immune to electrical surges.
You should put your cable modem on a surge strip. This is important as lightning may enter the modem and then attempt to leave via the AC wiring, specifically the hot wire, damaging other gear on that same leg. Tripp Lite makes a number of good models. If you are particularly paranoid you might want to put the modem on it's own surge device, though honestly I put all of my networking devices on a UPS / Surge protector together.
If you have followed all of my advice, above, you have protected your home and taken major steps to protect your network but the cable modem will still remain the most vulnerable. Think of it as a sacrificial component in your multi-stage protection.
The Details
Grounding surge protectors for Ethernet have been identified as causing damage to be more likely than without them. The technical issue is that they may convert common mode surges to differential. When that happens the downstream devices are 10-100x more vulnerable to damage. Isolators tested to UL 60-601 are better. We've seen very expensive isolators with TVSS we would recommend but ouch, the cost. You are better off running fiber.
Indoor Wiring
As we mention above, even with outdoor GDT suppressor and a surge strip some level of lightning surge voltage may still make it into the cable modem. Once inside that surge could propagate through every other wire coming out of it all the way down to your home entertainment center and all those devices. We want to add protection between the cable modem and your internal Wifi router. For this reason we discourage the use of combined modem/routers if you plan to wire all your Ethernet cables to it.
There are two solutions here. Use an Ethernet isolator, which we cover above, super simple. Another is to create an air gap via the use of
Ethernet/fiber converters which is what I do. If you want to get super fancy you'd use an Ethernet/fiber converter along with a
Wifi router with built in SFP+ port allowing you to go to your router directly via fiber. Pay attention to the connector type, LC vs. SC before ordering SFP modules and cables.
Personally I use a single Ethernet/fiber converter, a 1m fiber cable which feeds a home office router with built in SFP port which then short Ethernet to my Wifi router. It's a work thing. The point is that there is no metallic path from the outside coax to my indoor routers except via potentially the household AC wiring.
If you feel comfortable with either solution the fiber air gap is a better solution than the isolator. It is also very much recommended if you want to place your wifi router at some distance from the cable modem.
Beware Long Ethernet Runs!
One last thing to be concerned with is the potential for an electromagnetic pulse (EMP) from a lightning strike to induce a surge in metals. All the wiring in your home is susceptible to this and the longer it is the better of an antenna it will be. If you have Ethernet cable runs in your walls of longer than 20' you should
consider an isolator at the end, closest to your most expensive equipment. I have two, one at my home office switch and one before my home theater's switch as well. Of course, this leaves your wifi router vulnerable, so if you want to buy one for each end go ahead.
Obviously, if you can afford it, running fiber inside your home for long runs is ideal.
To be clear, our recommendations in regards to internal Ethernet wiring is that we cannot prevent the high voltage potential from an EMP, but we can attempt to isolate the damage. It's better to fry a single Wifi router than to attempt to pull a high current surge through the wall to reach even more gear, and also still fry the router.
Wifi Surges
One way in which Wifi is clearly superior to Ethernet is that a wifi signal won't propogate an electrical surge. Your phone or tablet, unless charging, will never get burned out because lightning entered your home via a cable modem and your wifi router. It just won't happen, but your chargers are absolutely vulnerable to surges which can make it to the devices they are charging.
Beware the use of an access point though. If you use Ethernet to the basement and then use an access point to enhance your Wifi signal there make sure it's on a surge protector or you run the risk of the Ethernet providing a surge path to your basement AC.
