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I'm running a long Ethernet cable between my garage and home (50m). How do you guys protect your long cable runs (and thus your equipment) from lightning surges? House is separate from the garage. About a 15m 20mm PVC ducting section underground between garage and house, and then the rest up in the roof (a portion running on the outside of a wall). I was thinking of using APC Ethernet ProtectNet surge protector on both ends, however it requires a ground connection.

So 2 questions:

  1. Can I connect this to my mains ground?
  2. Will a large surge cause the mains to trip?
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  • Not sure how the makers of that product can justify the claim "ensures complete protection of your equipment from surges". Lightning has already jumped a huge air gap, what makes them think it won't jump a couple more inches? It might be ok for other types of surges, but I doubt it can stand up to a nearby or direct lightning strike.
    – CactusCake
    Jul 7, 2017 at 14:10
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    Marketing Hype - there will be fine print that takes away what the large print offers, or they may have an "equipment replacement insurance" which might or might not be easy to use (probably often has some sort of weasel-clause where they claim you didn't install it correctly and they don't pay.) Pretty much nothing survives a direct hit. But there are many things that get damaged by a "nearby" hit, which might be miles away but causing surges in various systems. For those, a surge suppressor may help. Fiber is ideal, since it electrically isolates the data systems it connects.
    – Ecnerwal
    Jul 7, 2017 at 15:15

3 Answers 3

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Best option - get an outdoor-rated fiber patchcord, SFPs, and switches with SFP slots for each end. You have the duct in place, this should be simple enough. Prices have come way down.

If you use the wired method, the wiring /surge device should be bonded to the house and garage grounding systems at the service entrance to each building. Using a shielded cable so you can ground the shield may be beneficial.

Typical cheapest, easiest, good-enough method for most homeowners (since fiber requires replacing your network hardware in most cases) is a point-to-point or mesh 802.11ac wireless link. This may also improve the heck out of your WiFi, depending what you have now. Not as fast as a wire or fiber, but faster than most service to the home.

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  • I have considered the SFP fibre route, however I can only get them pre-terminated (and I dont have the skill to terminate them myself anyway). Regardless, I have big doubts that the LC connector would make it through my conduit given that it needs to go around bends, and that the connector is 18mm on its widest side. Wifi is an option, but my fibre internet connection will terminate in the garage, so would prefer wired solution for low latency ;-). The information I was struggling with, was the point where to earth to. Thanks for clearing that up!
    – Jurgen Strydom
    Jul 10, 2017 at 7:53
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If you put the surge arrester on the house side of the wire run, you can hook it into mains ground. However, if the entry point is far from your load center, I'd recommend using a grounding rod buried next to the entry point. (In general, you want surges to pass to earth ground in the least possible.

Free advise: (I've run Ethernet cable from a WAN radio tower to my house for the last 12 years and have seen 7 events)

  1. Run your cable into a sacrificial hub/switch/cheap router.
    Better to kill a $10 4-port switch than a port in an expensive router.
  2. Keep spares for everything relevant. Keep something nearby to patch the surge suppressor out of the wire if you need to test it. Have a spare ready for whatever you connect the wire to (router, switch, etc.) You don't want to have the connection die and have no ability to troubleshoot and no ability to get back running.
  3. Keep your router/network configuration backed up and documented. Document it knowing that you'll have plenty of time to forget the specifics before your first event, but you will eventually have that first event.
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    If you add another ground rod, that ground rod must be bonded to your grounding system - if not, it quite literally makes things worse not better. It is actually best (for a wired system) to re-route the cable run out of the house (and into the garage) to be near the service entrance for the building, so that short, direct access to the SE ground is practical.
    – Ecnerwal
    Jul 7, 2017 at 15:49
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You want your grounding system to be tip-top.

In new work, the correct grounding system is:

  • A grounding system (ground rods etc.) at the house
  • Another grounding system (ground rods, whole nine yards) at the detached building
  • The two grounding systems connected to each other by the grounding wire in the AC power cable which supplies the detached building from the main (or vice versa).

This can be bypassed in some cases, for instance if you have a single circuit powering the outbuilding. (no subpanel).

So your first step is to bring your current grounding system up to current code.

The upshot is that your ethernet cable has not a ghost of a chance if it's asked to carry lightning currents, and the electronics on both ends have no chance if exposed to lightning voltage. You want to pull lightning away from your electronics, e.g. by having proper lightning rods on the buildings. When lightning strikes, there will still be a several thousand volt voltage differential between the house grounding and the outbuilding grounding, that can't be avoided.

I would put an expendable electronic device on each end of the run, like a hub or ethernet amplifier. And make sure that equipment is properly grounded.

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  • Thank you for the information. I agree, with a close by strike it is tickets no matter what you do. The house is pretty new so it should be up to code, just not sure what the standard of this code is in South-Africa ;-).
    – Jurgen Strydom
    Jul 10, 2017 at 8:00

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