Q: Recently, mice chewed through a section of fiber-optic zipcord located inside one of our trailer offices. The cable is an Opti-Pak ofnr-rated product manufactured by APD Inc. [Applied Photonic Devices (Danielson, CT) is now the General Photonics division of General Cable.] The rodents chewed completely through, severing the jacket, Kevlar, and fiber. I know that outdoors, fiber cable is armored or put into innerduct and conduit to prevent rodent attack, but what about inside buildings? At one time or another just about any building has mice. Are occurrences like ours common? Do you know if some cable-jacket formulations are more attractive to rodents than others? Is there any reference work on this subject? To my knowledge, we`ve never had a copper cable attacked in this way. We replaced the damaged zipcord today, but are there any other precautions we should take? Mousetraps come to mind.
A: To answer Ron`s questions, let`s start with whether or not other people have had this problem with copper cables. William Sewell, who is with Sverdrup (Arlington VA), writes that mice or rats will chew copper cables as well. Bill said that he received the following questions from the owner of a new, 11-story, 1-million-square-foot building in Washington, DC.
"On a walk-through with the contractor," said the building owner, "we saw locations on the third floor where damage was being caused to cabling by rats living under the floor. The contractor has begun testing and found locations where the cable failed Category 5 testing due to being eaten by the rats.
"How do we find all of the locations where damage to the cabling is being caused by the rats? Is it possible that a partially-eaten cable will pass testing today and develop problems in the future? If the rats remain under the floor, could they damage a cable next week that the contractor tested and passed this week?"
Many projects require that optical-fiber cable be installed in innerduct inside and outside of buildings. While the designer will tell you that this level of protection is necessary to protect against mechanical abuse, none that I spoke with were thinking of rats.
Rodents chewing cable is so common a problem that outside-plant cable is available with gopher-resistant sheathing. Telecommunications cable is a preferred target because of size, not taste or smell. While I cannot find any written reports on this subject, I will forward this question to the appropriate nema [National Electrical Manufacturers Association, Washington, DC], icea [Insulated Cable Engineers Association, South Yarmouth, MA], and TIA groups for their consideration.
As for answers to Bill`s questions, to locate all the damaged areas, physical inspection is your best bet. Rat munches are not specifically covered in any performance standard of which I am aware, but in my opinion the cable geometry has been altered and it is likely that the sheath, and possibly the conductor insulation, is missing in places. That can definitely cause problems in the future. If rats were under the floor and chewed the cable, there is a better than even chance that if one or the other is not removed, the rats will chew the cable again.
Donna Ballast is a communications analyst at the University of Texas at Austin and a bicsi registered communications distribution designer (rcdd). Questions can be sent to her at Cabling Installation & Maintenance or at PO Drawer 7580, University of Texas, Austin, TX 78713; tel: (512) 471-0112, fax: (512) 471-8883, e-mail: email@example.com.