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A power strip with a surge rating protects one path into your equipment. Surges that destroy modems, routers and switches frequently arrive by a different route entirely — down the coaxial drop, along an Ethernet run to an outbuilding, or through a difference in potential between two separately grounded points in the same house. Understanding those paths is most of the work; the gear is comparatively simple.
One clarification first, because it saves money: fiber does not conduct. A glass fiber drop cannot carry a surge into your house. If your service is fiber to the home, the risk moves entirely to the power side and to any copper that leaves the building. That is a meaningful simplification, and it means fiber households should spend their budget differently than coax households.
The three paths a surge actually takes
| Path | How it reaches your gear | Applies to |
|---|---|---|
| Power | Through the service panel and out to the outlet the equipment is plugged into | Every household |
| Coaxial drop | Along the shield and center conductor from the aerial or buried cable drop | Cable internet, and any home with a coax entry — including disused ones |
| Copper data runs leaving the building | Ethernet to a detached garage, shed, camera, or wireless access point on an outbuilding | Anyone with a run that goes outside |
The second and third are the ones people miss. A nearby strike does not need to hit your house; it raises ground potential in the area, and if two parts of your system reference different grounds, current flows between them through whatever connects them. Very often, what connects them is a network cable and the equipment at each end.
An Ethernet run to a detached garage, with the garage on its own subpanel and its own ground rod. A nearby strike lifts one ground relative to the other, and the only bridge between them is the Ethernet cable. The switch at each end dies; everything else survives. This is extremely common and almost never anticipated.
Bonding and grounding, briefly
Two words that get used interchangeably and mean different things.
Grounding connects a system to earth. Bonding connects the grounded parts of different systems together so they sit at the same potential. For surge purposes, bonding matters more, because damage comes from a difference between two points rather than from the absolute value at either one.
In practical terms, the coax entry block, the telephone or fiber network interface device, and the electrical service should all be bonded to the same grounding electrode system. When they are, a surge that raises the potential of one raises all of them together and there is no path through your equipment. When they are not, there is.
Bonding at the service entrance is governed by electrical code and is not a casual weekend project. If your coax entry has no visible bonding conductor, or the bond runs to a separate rod rather than to the main grounding electrode system, that is a conversation for a licensed electrician. The devices in this guide assume a correct bond exists — without one, they do very little.
Coax entry protection
If cable enters your home, there should be a grounding block where it does: a small fitting that passes the signal through while bonding the cable shield to the grounding system. Most installations have one. Many have one that was correctly installed years ago and has since corroded, been disconnected during other work, or been bypassed by a later drop.
Beyond the grounding block, a coaxial surge protector adds a gas discharge tube or similar device that clamps a transient on the center conductor as well as the shield. Frequency range matters — a protector rated for an older, narrower band can attenuate the upper frequencies newer cable systems use, so check that the passband covers the full range your service uses.
- Locate the coax entry and confirm a grounding block is present
- Confirm the bonding conductor runs to the main grounding electrode system, not a separate rod
- Check for corrosion — outdoor blocks age badly and a green connection is not a connection
- Verify the protector's passband covers your service's full frequency range
- Check any disused coax entries; an abandoned drop still bonded is fine, unbonded is not
Ethernet that leaves the building
Any copper Ethernet run that exits the building envelope is a surge path. The three mitigations, in increasing order of effectiveness:
Ethernet surge protectors at each end of the outdoor run, bonded to ground. These clamp transients on the data pairs. They are inexpensive and they are the minimum for any outdoor run. Note that a protector needs a real ground connection to do anything — one screwed to a plastic box accomplishes nothing.
Shielded cable, correctly bonded at one end only. Shielded Ethernet with the shield bonded at both ends can create the exact ground loop you are trying to avoid. Bonding at one end is the general practice for this reason.
Fiber instead of copper. If the run is to a detached structure, a fiber link with a media converter at each end breaks the electrical path completely. There is no conductor, therefore no surge path, therefore nothing to protect. For a permanent run to a garage, shed or barn this is the correct answer and it is not expensive.
If you are running a network link to a detached structure and you have the choice, run fiber. Surge protectors reduce risk; fiber eliminates the entire category. A pair of media converters and a run of outdoor-rated fiber costs less than replacing the equipment at both ends twice.
The power side
Power protection is a layered problem. A whole-house surge protective device at the service panel handles the large transients arriving from outside; point-of-use protection at the equipment handles what gets through and what originates inside the house.
For network equipment specifically, an uninterruptible power supply is usually the better buy than a plain surge strip. It provides surge protection, it rides through the brief interruptions that cause equipment to reboot, and in many households the brownouts and momentary dips are a far more frequent cause of trouble than actual lightning ever will be.
Two selection notes. Look for a unit with automatic voltage regulation if your supply sags — that is the feature that handles low voltage without draining the battery. And size for runtime rather than for capacity: a modem, ONT and router together draw very little, so a modest unit can carry them for a long time.
What to buy
Categories rather than specific models, because model availability turns over constantly and the right choice depends on which paths your house actually has.
Coaxial grounding block and surge protector
$ · Entry-level protection, essential rather than optional
Passes the signal while bonding the shield and clamping transients on the center conductor. Check that the rated passband covers the full frequency range your service uses, and that it is rated for outdoor use if it mounts outside. This is the highest-value single item for any home with a coax entry.
Gigabit Ethernet surge protector, pair
$ · One at each end of any run that leaves the building
Clamps transients on the data pairs. Buy in pairs — protecting one end and not the other leaves the path open. Confirm the unit passes the speed you need, and if the run powers a device, confirm it passes Power over Ethernet at the standard your equipment uses. It must be bonded to ground to function.
Fiber media converter pair with outdoor-rated fiber
$$ · Eliminates the surge path entirely rather than mitigating it
Converts Ethernet to fiber at one end and back at the other, breaking the electrical connection between structures completely. Choose single-mode for longer runs and direct-burial or armored jacket for buried paths. For a permanent link to a garage, shed or barn this is the correct engineering answer and it costs less than replacing switches repeatedly.
Line-interactive UPS for network equipment
$$ · Surge protection plus ride-through for brief outages
More useful than a plain surge strip for network gear, because brief interruptions and voltage sags cause far more equipment reboots than lightning does. Look for automatic voltage regulation if your supply sags, and size for runtime rather than capacity — a modem, ONT and router draw little, so a modest unit runs them a long time.
Panel-mounted surge protective device
$$ · Installed at the service panel by an electrician
Handles the large transients arriving on the power service before they reach branch circuits. This is a complement to point-of-use protection rather than a replacement for it, and it is electrician-installed work. Worth combining with a check that your coax and network interface bonding is actually correct while someone qualified is already at the panel.
Getting it right
Three errors account for most of the protection that does not work.
Protectors that are not grounded. A surge protector diverts energy to ground. With no ground connection it is an expensive pass-through. Every device in this guide needs a real bond to the grounding system.
Multiple separate ground rods. Driving a rod for the network gear and another for the electrical service creates precisely the potential difference that destroys equipment. Everything bonds to one grounding electrode system.
Protecting one path and ignoring another. A surge takes the path that exists. Protecting power while leaving an unbonded coax entry open simply routes the damage through the coax. Walk the whole building envelope and account for every conductor that crosses it.
Frequently asked questions
Does fiber internet need surge protection?
The fiber itself does not — glass does not conduct, so a fiber drop cannot carry a surge into the house. The ONT still needs power protection, and any copper Ethernet leaving the building still needs protecting. Fiber households should spend their budget on the power side and on outdoor Ethernet runs rather than on entry-path protection.
What is the difference between bonding and grounding?
Grounding connects a system to earth. Bonding connects the grounded parts of different systems together so they sit at the same potential. For surge damage, bonding matters more, because equipment is destroyed by a difference in potential between two points rather than by the absolute value at either one.
Why did a nearby lightning strike kill my network switch but nothing else?
Almost always a ground potential difference bridged by a data cable. A strike nearby lifts ground potential in the area; if two parts of your system reference different grounds — for example a detached garage on its own rod — current flows between them through whatever connects them, which is the Ethernet cable and the equipment at each end.
Do I need surge protectors on Ethernet running to a shed or garage?
Yes, at both ends, bonded to ground. Better still, run fiber with a media converter at each end instead. Fiber has no conductor, so it eliminates the surge path entirely rather than mitigating it. For a permanent link to a detached structure that is the correct answer and it costs less than replacing equipment repeatedly.
Is a UPS better than a surge strip for a modem and router?
Generally yes. A UPS provides surge protection and also rides through the brief interruptions and voltage sags that cause equipment to reboot — which in most households are a far more frequent cause of trouble than lightning. Size for runtime rather than capacity, since network equipment draws very little.
Can I install a coax grounding block myself?
The block itself is simple, but the bonding conductor and where it terminates are governed by electrical code, and getting that wrong makes things worse rather than better. If your coax entry has no visible bond, or the bond runs to a separate rod instead of the main grounding electrode system, involve a licensed electrician.
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