Learn the many purposes of grounding. For example, that
cable shield is grounded only for noise or EMI reduction.
Proper shielding is 'grounded' only at one end so that shield
does not conduct currents other than the noise. This
grounding is different than grounds for human safety and
Surge protection is essential for any cable between two
buildings because each building is a lightning rod that
directs a surge into other building's ground via ethernet
electronics (ie hubs). Grounding for surge protection and
human safety means incoming wire must connect less than 10
feet to a single point earth ground. Same earth ground used
by phone system and AC mains. In your case, each ethernet wire
must connect 'short to earth ground' via a surge protector.
Surge protector only shorting wire to ground during a surge.
Surge protectors are effective when a wire connects to earth
during the surge. Connection to earth is what an effective
surge protector does. Therefore wire must first enter each
building at the same location that all other utilities also
enter building and must be earthed to same earth ground.
1) Grounding to an electrical outlet is not earth
grounding. Again, that outlet is most certainly more than 10
foot from central earth ground. 2) Does not matter that wire
is underground - as explained above.
Installing for effective electronics protection is not
difficult. Protector on each end of ethernet cable where wire
enters building (same concept is also installed in phone
system) is available as:
To better understand why surge damage is not a problem for
interconnected buildings using copper wire, visit a two thread
discussion in the newsgroup misc.rural:
Storm and Lightning damage in the country 28 Jul 2002
Lightning Nightmares!! 10 Aug 2002
or http://tinyurl.com/ghgv and http://tinyurl.com/ghgm
Surge enters building 1 on AC mains. Surges seek every
earth ground, destructively. Surge finds earth ground via
buried ethernet cable and ethernet hub in building 2. That is
how buried wire surges destroy electronics. That is why every
incoming wire must first connect to a buildings central earth
> I'm helping a small private school link ethernet networks across two
> buildings about 90 feet apart using copper category 5/5e cable. I've located
> a source of OSP twisted-pair cable (the gel type, with copper braiding).
> There is already a large diameter nonmetallic conduit between the two
> buildings, with two similar cables already in place for a PBX phone system
> (and a pull string). The shields of these CAT5 phone cables are grounded at
> each end. I plan to do similar grounding with my new cable.
> Inside one building, an empty conduit is available from the entry point to
> the wiring closet. Unfortunately, this conduit spans 85 feet, too long for
> the OSP cable to run indoors. (I'm guessing the conduit may be empty because
> the telephone people realized the distance was too long, so they took a
> diagonal direct route for their OSP cables to stay at the 50-foot limit.)
> I have questions about grounding the new cable:
> 1) I need to transition to indoor cable near the point of entry, but
> grounding will be difficult. Can I run a ground wire 6 feet or so to a
> nearby electrical outlet's ground? Or is it better to run a ground wire
> alongside the UTP cable in the 85-foot conduit and ground it in the wiring
> closet along with everything else? Is there a better solution?
> 2) Is it true that because my underground run is under 140 feet, I do not
> need lightning/surge protection at my entry points? (The conduits come out
> of the ground at the building exteriors, rise about 2 feet to a nonmetallic
> access point which directs them 90 degrees into the buildings.)
> 3) It would help if I could find the applicable electrical/networking codes.
> I haven't been able to find them on the web (except for sale at ridiculous
> Thanks very much for your help and suggestions.
> P.S. I know fiber optic would be a safer way to go, but this is a very small
> (i.e., broke) school. I've also considered wireless but this would cost four
> or five times more than copper. We're just trying to connect some simple
> Linksys equipment to share an internet connection.