Grounding armored fiber - best methods
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Grounding armored fiber - best methodsExpand / Collapse
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Posted Thursday, February 10, 2011 8:56 PM
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Does anyone have recent experience with the correct method to ground armored fiber optic cable?

Specifics - OFNP armored fiber cable routing between several floors from MDF to IDF.

We currently are grounding one side of armored cable and have been told by consultant that it is necessary to ground both sides.

Is this correct and would this cause a ground problem if using ground electrodes from different floors.

Also have armored fiber between buildings, and have been requested to ground each end of fiber. I will assume this may cause a ground problem having two ground sources?

Thanks for anyones help.

Post #5755
Posted Friday, February 11, 2011 7:12 AM


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Ribo (2/10/2011)
Does anyone have recent experience with the correct method to ground armored fiber optic cable?

Specifics - OFNP armored fiber cable routing between several floors from MDF to IDF.

We currently are grounding one side of armored cable and have been told by consultant that it is necessary to ground both sides.

Is this correct and would this cause a ground problem if using ground electrodes from different floors.

Also have armored fiber between buildings, and have been requested to ground each end of fiber. I will assume this may cause a ground problem having two ground sources?

Thanks for anyones help.

In practice, we only ground one end. Typically this is done at the MDF for either of the scenarios you list. If in doubt if this consultant is correct, check with your AHJ for local clarification.

Joseph Golan, RCDD (Retired)

Palm Coast, FL

Post #5756
Posted Tuesday, February 15, 2011 9:58 AM
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Your TGB located in the TR of each floor should be bonded to the AC electrical panel board which in turn is bonded to the building frame or other applicable AC grounding source (12th edition 9-19). If this grounding system is in place then you can ground both ends of the cable armoring without causing differences in ground potential. This is a best practice so as to always provide the shortest possible distance a hazardous voltage would travel down the armoring before being safely routed to ground. Alternately, a Telecommunications Bonding Backbone (TBB) can be installed.
Post #5770
Posted Tuesday, February 15, 2011 10:10 AM
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Thanks.

I am just trying to figure out what method is correct or best practice.

I have conflicting info from Commscopes Armored cable installation specifications as to what method to use.

They indicate grounding both ends if using metallic connectors into a metallic pull box or termination frame.

They also indicate that grounding one end only when cable does not terminate in metallic box is ok.

This seems to be a gray area that the manufactures should clarify for their system.

Post #5771
Posted Thursday, March 10, 2011 11:58 AM
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Shouldn't cause a ground problem since it's fiber.  If it were copper, and you had a ground loop creating EMI on the pairs then it's a performance issue, but it's not.

If it's stated on the drawings and specs to ground both ends I'd do it.

Derek Allison, RCDD/OSP, CSI CDT

Post #5842
Posted Thursday, March 10, 2011 6:19 PM
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Derek A. (3/10/2011)
Shouldn't cause a ground problem since it's fiber.  If it were copper, and you had a ground loop creating EMI on the pairs then it's a performance issue, but it's not.

If it's stated on the drawings and specs to ground both ends I'd do it.

Although not specifically stated by the OP, I would imagine the concern is more about bonding 2 separate grounding systems, that may have a difference of potential, using only the armored sheath of a telecommunications cable.

Post #5847
Posted Thursday, March 10, 2011 7:14 PM
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Thanks,

Yes, that is my concern. Having (2) separate ground sources connected to one metallic cable jacket that is feeding two buildings.

Post #5848
Posted Friday, March 11, 2011 10:33 AM


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Derek A. (3/10/2011)
Shouldn't cause a ground problem since it's fiber.  If it were copper, and you had a ground loop creating EMI on the pairs then it's a performance issue, but it's not.

If it's stated on the drawings and specs to ground both ends I'd do it.

Derek,

I don't think I have ever seen a ground loop cause EMI but I am only in the business for 40+ years and still learning.

I would be more interested in that the grounding of the armor at two different points having a difference in potential [voltage] and conducting current over that armor due to those differences of potentials.

Joseph Golan, RCDD (Retired)

Palm Coast, FL

Post #5849
Posted Monday, March 28, 2011 2:30 PM
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HoustonCCNP (3/10/2011)
Derek A. (3/10/2011)
Shouldn't cause a ground problem since it's fiber.  If it were copper, and you had a ground loop creating EMI on the pairs then it's a performance issue, but it's not.

If it's stated on the drawings and specs to ground both ends I'd do it.

Although not specifically stated by the OP, I would imagine the concern is more about bonding 2 separate grounding systems, that may have a difference of potential, using only the armored sheath of a telecommunications cable.

 

Actually, the OP does mention it:  "Also have armored fiber between buildings, and have been requested to ground each end of fiber. I will assume this may cause a ground problem having two ground sources?"

Derek Allison, RCDD/OSP, CSI CDT

Post #5921
Posted Monday, March 28, 2011 3:15 PM
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JPGolan RCDD (3/11/2011)
Derek A. (3/10/2011)
Shouldn't cause a ground problem since it's fiber.  If it were copper, and you had a ground loop creating EMI on the pairs then it's a performance issue, but it's not.

If it's stated on the drawings and specs to ground both ends I'd do it.

Derek,

I don't think I have ever seen a ground loop cause EMI but I am only in the business for 40+ years and still learning.

I would be more interested in that the grounding of the armor at two different points having a difference in potential [voltage] and conducting current over that armor due to those differences of potentials.

 

The TDMM refers to ground loops throughout, and does mention it causing EMI, which is why I responded the way I did.  Sorry, I can't speak to your 40+ years.  Keep in mind I was clear with what I stated mentioning "if it were copper...., but it's not"

To elaborate, my point was to answer the OP question of "....would this cause a ground problem if using ground electrodes from different floors."  The only potential "problem" I know of when grounding both ends of a cable is when you're in the copper cable world, which would be a ground loop causing EMI on the copper conductors.  If you do have a ground loop problem, you disconnect one end from the grounding system (at least this is what the mfgs tell us).  My response was more informational for the OP since we sometimes bleed our thoughts from the copper world to the fiber world.  Obviously, EMI is not an issue when using optical fiber, so there won't be any "problems".

Now, having said all this, there is some confusion I didn't point out earlier, but now it seems appropriate since there is still some confusion.  The OP states OFNP when routing between floors, but I assume he's referring to OFCP, or OFCR.  If OFNP, obviously there is nothing to ground.  If OFCP or OFCR the NEC is somewhat vague in whether or not you ground both ends or one end .  The best, and standard practice is to ground both ends, however.  An AHJ can interpret it either way, so it's best to do what the designer specified.

The second part of the question:  "Also have armored fiber between buildings, and have been requested to ground each end of fiber. I will assume this may cause a ground problem having two ground sources?"  Code requires Entrance Cables with non-current-carrying metallic members to be grounded at both ends, and is quite clear.

I hope this helps to clarify...


 

Derek Allison, RCDD/OSP, CSI CDT

Post #5922
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