Twisted Pair and electrical storms

I have an aerial network cable run between two buildings approaching the 100 meter limit for ethernet.
We lost a coax media adapter to an event, presumably lighting last year, and sometime recently a $400 wireless access point after I converted to twisted pair.
How can I protect this run? I have to cross a street and can’t bury it.

I assume you’re using CAT-5 ethernet? If so, then something like this will help. Nothing will protect 100% against direct lighting strikes, but these devices should minimize the damage to connected equipment. You’ll want one at each end of the outdoor cable run. They’d be mounted and grounded inside as close to the entry point as possible.

Here’s a source that sellslightning protection kits for cable. There are probably many others. I Googles “cable lightning protection.”

Most of the campuses that I’ve seen use fiber optics for all inter-building links. Besides being immune to lightning strikes and surges, it avoids problems with electrical differences between buildings, which can also destroy cables and equipment.

Not sure if it is appropriate but you might also check with the ham-radio community. Those folk are in constant dread of lightning and have some very clever ways of avoiding it. I have seen one lightning arrestor that actually used an old automotive sparkplug with one end grounded.



He already did. :smiley:
73 de KB2YYR

How are you terminated at each end?
Are you transmitting at 100 mbps?

The least expensive way to protect your twisted cat5e is to terminate it at both ends using either 110 blocks or 66 blocks and installing sneak fuses accross the pairs. You do know that the data is transmitted on conducters 1,2,3 & 6 respectively using 568b wiring map. I sill would apply sneak fuses accross all 4-pr.

You should also consider stranding shielded cable. Anytime you install an aerial cable you are subject to RF interference, this will corrupt your data transmission and will drive you crazy trying to isolate your trouble. Remember, just ground one side of the shielded cable.

Keep all your terminations tight and as close to the blocks as possible. If not, your 100 mbps may end up 10 mbps. Sneak fuses are cheap, however, effective.

Thanks everyone.
I’m looking at Q.E.D.'s link and next time we’ll run shielded TP.


Well, good. Makes ME feel smart. :stuck_out_tongue:


There are many companies around that insert electrical wires underground without digging up in between, they just insert it underground at one location and it comes up at or near the desired location on the other side of the street. I’ve seen this done across a parking lot much wider than the average street.

So, physically, this could probably be done. And the price is fairly reasonable, too.

Are you saying it “can’t” because you didn’t know about this, or because you anticipate problems getting legal permission to do this under a street?

We’re crossing a street on campus. The cost of cutting through pavement would be prohibitive.

If you’ve already got the cable installed, I’d go with a pair of the protectors that Q.E.D. referenced. APC has similar items, but are incompatible with PoE - power over ethernet - which is getting to be a pretty popular way of powering distant routers, hubs and access points.

If this were a new install, have a look at setting up a Wi-Fi link using WPA encryption and highly directional antennas (such as the famed Pringles can design) so someone would need to be pretty much right between (or directly behind) the antennas to intercept the traffic. Another good choice would be fiber as it’s immune to lightning, surges, and hackers.

Lightning protection devices are usually effective, however… A lightning strike has travelled several miles to get to your building, and it might jump right past even the most elegant protection device. Lightning sometimes won’t listen to sound engineering logic. It can be darned unreasonable.