Grounding rack for sheathed fiber optic cable
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Posted by sphealey on August 11, 2005, 3:31 pm
Please log in for more thread options We are going to be routing 12 metallic-sheathed fiber optic cables across our plant floor (usual mix of 480V, welding, etc) and into the datacomm room. It seems to me that the metallic sheath should be grounded at the point where the cables enter the room, to drain off any induced voltages on the sheath. In the dim past I used IBM Type 1 cable, and the termination racks had a tower that the cable would run through. You would strip off 1 cm of the insulation at the point where the cable ran through the tower and crimp a tab on the tower onto the metallic shield, then ground the tower. I would think this should work for the fiber cables also. However, I can no longer locate any such part. Any suggestions? Thanks. sPh | ||||||||||||||||
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Posted by Alexander Burke on August 11, 2005, 11:42 pm
Please log in for more thread options Fiber optic cabling makes no use of electromagnetic signals, and is therefore immune to even incredibly-high levels of electromagnetic interference. Solid heavy metallic conduit should protect the cables nicely from physical impact, welding sparks, etc. No grounding is necessary from a data point of view. | ||||||||||||||||
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Posted by sphealey on August 12, 2005, 10:43 am
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Indeed. [...] > Solid heavy metallic conduit should protect the cables nicely from
> physical impact, welding sparks, etc. Unfortunately, from a life-safety and equipment damage point of view fiber optic cables with metallic sheaths and/or metallic strength members, such as the indoor/outdoor armoured cable we are using for this application, can develop voltages and current flows from induction on the sheath or leakages from power cables that it may cross or parallel. Corning Cable Systems has a white paper on their site discussing this. In the specific case, besides the usual plant induction and leakage possibilites, one run will be passing through a 24kV transformer/switchgear enclosure so the possibility for induction is high. I was fortune enough on my first fiber optic project many years ago to be teamed up with a power systems electrical engineer who walked me through all this, so it has been a bit of an obsession of mine since! sPh No grounding is necessary from a data point of view. | ||||||||||||||||
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Posted by Jgolan on September 7, 2005, 2:51 pm
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You are absolutely coprrect that the metalic portion of the cable needs to be grounded. If this is a BX or greenfield type construction of tyhe cable, the easest way is to use groundable connectors made of BX or Greenfield and then run a grounding conductor from the connector to a ground bar. Joe Golan, RCDD ------------------------------------- sphealey wrote: > > Fiber optic cabling makes no use of electromagnetic signals, and
>> is >> therefore immune to even incredibly-high levels of electromagnetic >> interference. > Indeed.
> [...]
>> Solid heavy metallic conduit should protect the cables nicely from
>> physical impact, welding sparks, etc. > Unfortunately, from a life-safety and equipment damage point of view
> fiber optic cables with metallic sheaths and/or metallic strength > members, such as the indoor/outdoor armoured cable we are using for > this application, can develop voltages and current flows from induction > on the sheath or leakages from power cables that it may cross or > parallel. Corning Cable Systems has a white paper on their site > discussing this. > In the specific case, besides the usual plant induction and leakage
> possibilites, one run will be passing through a 24kV > transformer/switchgear enclosure so the possibility for induction is > high. > I was fortune enough on my first fiber optic project many years ago to
> be teamed up with a power systems electrical engineer who walked me > through all this, so it has been a bit of an obsession of mine since! > sPh
> No grounding is necessary from a data point of view.
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Posted by Watson A.Name - \"Watt Sun, th on September 10, 2005, 4:41 am
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[snip] > > In the specific case, besides the usual plant induction and leakage
> > possibilites, one run will be passing through a 24kV > > transformer/switchgear enclosure so the possibility for induction is > > high. Q: You have signal cables running thru two different electrical enclosures. One enclosure has a 24kV electrical cable carrying ten amps. The other enclosure has 240VAC at 100 amps. Which of the signal cables is going to get the most induced current? A: Since the 24kV cable is shielded, there is going to be very little electrostatic induction from it (we have 4160 VAC cables underground, and they are shielded, too). The signal cable will have little electromagnetic induction from the ten amps of the 24kV cable. But the signal cable in the 240VAC, 100A enclosure will have up to 10 times as much electromagnetic induction as the 24kV enclosure. | ||||||||||||||||
> therefore immune to even incredibly-high levels of electromagnetic
> interference.