OSP Cat5/5e grounding question

OSP Cat5/5e grounding question

Post by Russ » Fri, 18 Jul 2003 13:35:33



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
prices.)

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.

 
 
 

OSP Cat5/5e grounding question

Post by Justin Ti » Fri, 18 Jul 2003 21:25:37



> 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.

So far, so good.  Be sure to leave a pull string in place for the next
time someone has to go into that conduit.  You didn't say the diameter
of the conduit, but I will assume it is at least 3 inches.

Quote:

> 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?

The first question is what kind of conduit?  If it is metallic, then
there is no problem running OSP cable for 85 feet.

Quote:

> 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.)

That assumption is false.  You will need to provide lightning/surge
protection for any conductor that is exposed to the possibility of
lightning.

Quote:

> 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
> prices.)

That's because they are all copyrighted materials and it is through
the sale of the printed documents the code writing agencies receive
the bulk of thier support.

Quote:

> 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.

As far as it being a small, "broke" school, running 6 strands of fiber
is not that expensive.  Leave an additional 15 feet or so of fiber at
each end and then beg someone to provide the terminations for two
strands at no cost to the school.  You may find that a parent does
this type of work for a living and would be willing to donate the
connectors and labor for a tax write-off.  They may even be willing to
provide media convertors if you need them.  Leaving the unused fibers
unterminated will give you expansion room in the future, but
unterminated fiber will deteriorate over a period of time.  The time
will depend on the environment which is why I said leave 15 feet of
slack cable at each end.

 
 
 

OSP Cat5/5e grounding question

Post by w_to » Fri, 18 Jul 2003 23:56:45


 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
transistor protection.

  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:
  http://www.tripplite.com/products/product.cfm?productID=151

  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
ground.


> 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
> prices.)

> 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.

 
 
 

OSP Cat5/5e grounding question

Post by Russ » Sat, 19 Jul 2003 01:58:24


Thank you for your advice. My responses are imbedded below:

Quote:> > 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?

> The first question is what kind of conduit?  If it is metallic, then
> there is no problem running OSP cable for 85 feet.

Unfortunately it is not metallic; it's PVC or ABS. And I learned from
another post that the ground must occur within 10 feet, and I can't use the
electrical outlet's ground. So I appear to be sunk.

Quote:

> > 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.

> As far as it being a small, "broke" school, running 6 strands of fiber
> is not that expensive. ....

Another concern with fiber is that I don't know if the underground conduit
can handle the required bend radius. Fiber seems to require much gentler
corners than copper; I already know the entry point to the building has two
very sharp 90-degree turns just to make it through the walls.
 
 
 

OSP Cat5/5e grounding question

Post by Justin Ti » Sat, 19 Jul 2003 23:11:13



> Thank you for your advice. My responses are imbedded below:

> > > 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.

> > As far as it being a small, "broke" school, running 6 strands of fiber
> > is not that expensive. ....

> Another concern with fiber is that I don't know if the underground conduit
> can handle the required bend radius. Fiber seems to require much gentler
> corners than copper; I already know the entry point to the building has two
> very sharp 90-degree turns just to make it through the walls.

From your description you have a minimum of four 90 degree bends.  Two
where it goes into the building and two where the vertical stub meets
the underground conduit.  If the conduit is large enough, you may not
have a problem with the bends at the bottom of the stubs and changing
the pull box on the outside of the building will help with that
situation.

I'm looking at a sample of Berk-Tek's Adventum loose-tube dry-gel
indoor/outdoor cable I just happened to have on my desk - no
endor*t implied.  The cable itself is just a little larger than a
Cat 5, but it is much stiffer.  It would take all of a 4" conduit 90
bend, but it could be pulled through.  Terminating this cable is more
involved than with a tight-buffer, but there should be no problem with
bend radius - IF the conduit has no more than the 4 nineties.

The biggest issue you will have to deal with in tight bends is
attenuation.  If your loss budget - the amount of light going into the
fiber over what you need at the receiver - is large enough, then for
the 85 feet of your run, no problem.  You just won't be able to get
600 MHz of bandwidth, but you will get something less.

Rodgers Platt

 
 
 

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