One of the buildings I support recently had an adventure with a broken fire sprinkler. Lots of water everywhere.

One of the "drains" the water used was the vertical risers between network closets. The cable plant in this building has bundles of cat5e as well as conduit with bundles of multimode fiber optic cables. The fiber is standard multi strand plenum rated stuff that terminates in boxes that have the patches to the switches.

As far as I can tell, no water got near the ends of the cables (fiber or copper) but the conduit was saturated, and is likely still saturated because there isn't any air flow to dry the cables out.

My gut reaction is that while it didn't do the cables any favors, it likely also isn't going to cause any problems. A little more reading / googling around leads me to believe that the water may cause problems down the road.

Some pretty pictures so everyone knows what I'm talking about:

Fiber conduit: Fiber conduit

Vertical riser, going down: Vertical riser, going down

Vertical riser, going up: Vertical riser, going up

Does anyone have any experience with this sort of damage and how to deal with it? Should we just ask the insurance adjuster to add "pull new structured cable" to the list of things to be replaced?

And, if the opinion is "replace it because it'll start failing randomly over time" please include links that describe the specific failure modes, so I've got some ammo to use with the adjuster.


The real danger is at the terminations, where corrosion can start. As for the cables themselves, they're fine in water, although I'd be careful using it in a corrosive solution. Keep an eye open and you should see plenty of examples of network cables, including fibre, used outdoors in the weather. I know of examples where cables sit permanently in water and have done so for many years. Network cabling is no different to any other kind of electric cabling. Keep the ends dry and the rest doesn't matter.

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    So the "outdoor" rating on cables just indicates that it is tougher than indoor plenum rated stuff, but both are waterproof? In random googling I found a reference to the outer layers of fiber being slightly water permeable, but google's rotten for searches like that so I couldn't find anything 100% either way. – chris Jan 5 '10 at 13:11
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    You're right about the outdoor rating meaning a tougher sheath but normal CAT cable is waterproof. It wouldn't even matter if water somehow got inside the outer sheath, as the inner insulation is also waterproof. As for fibre, my knowledge is much more limited but I would expect all fibre cables to have an outer waterproof sheath, otherwise normal atmospheric moisture would cause all sorts of problems. Certainly all the fibre I've ever seen does. – John Gardeniers Jan 5 '10 at 20:25
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    Fantastic typo! – MDMarra Jan 18 '10 at 21:56

Replacing the bundles would be expensive. If you've got it in your budget (or insurance will pay for it), do it.

As long as there were no nicks in the PVC sheathing, you should be alright (http://www.cat-5-cable-company.com/faq-bury-burial-cat-5-cable.html).

It's hard to tell if you had any nicks in the plastic, but I imagine that you're going to find out. Do you have any spare cables in the bundles? I would save yourself the time of panicking during an emergency and find and label them now. Create documentation on how to replace a poorly performing cable with a spare.

Know that if you don't rerun the cables, this event is going to be the scape-goat for all future network performance issues forever, until more cables are run.

  • Well, the rest of the building is actually worse off than the wire closet, so we may have to replace the wires just because the end user port end got soaked. – chris Jan 4 '10 at 20:20

I don't think the water will have any immediate effect as long as the water never entered the cables--obviously copper wiring will oxidize if given the chance.

My argument for re-running the cable would partly be that you can't reasonably ensure the current cable will dry instead of growing mold/mildew and turning into a slimy nasty mess.

  • The whole riser would have to have something done, wouldn't it? Otherwise new cable pulls would not help much with slime and gunk if it's just new cable running through what's already got crap growing...that could add a lot to the bill depending on how it's built, no? – Bart Silverstrim Jan 4 '10 at 16:39
  • I know mold can grow on anything, but has anyone got direct experience with plenum rated cables / conduits supporting mold? It's a disaster for the building because there will be mold growing between the floors. I wonder if facilities is going to bother with fixing that or not, though. – chris Jan 4 '10 at 16:42
  • @bart -- if we were to pull new cables we'd run new conduit as well, and then pull out the old conduit and dispose of it. The vertical risers are basically just holes in the floor / ceiling with cables running through them and foam to stop fires from propagating from one floor to another. – chris Jan 4 '10 at 16:44
  • yeah, this pretty much sums it up. let insurance pay for it if possible -- if not, you can revisit the question of whether it's worth the expense of having it done yourself. (good thought about new conduit; you'd really need to give the old stuff time to dry out before reusing it.) – quack quixote Jan 4 '10 at 16:44
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    Really, I would think you need someone who specializes in mold and damage repair to consult with this. Your mold growing issues will be beyond just the technology, your employer will have health issues for the employees and if it's to be repaired you need to have it all done now while the insurance company is assessing damage. My first thought would be needing to re-run everything parallel to what's currently in place and moving the connection over for your question, but if you have mold everywhere...bad problems later on. – Bart Silverstrim Jan 4 '10 at 16:45

Effect on Electrical Performance The ingress of water into the data cabling system can have a serious affect on its ability to support high bit rate data applications like Fast Ethernet and Gigabit Ethernet. In some cases, cables that are already near the link length limit (and therefore the attenuation budget) for the standard may fail after flooding. This is because when the cable gets wet, its dielectric performance is changed, which affects impedance and the related parameters of attenuation and return loss.

Cable Construction and Water Ingress It is a common misunderstanding that PVC, the material used to coat standard data cable, is waterproof. It is not; it is hygroscopic. Standard Category 5e and Category 6 cables have a PVC coating and are designed for indoor use and are not suitable for use in wet conditions.

Cables designed for use outdoors, where moisture or water is present in any quantity, incorporate waterproofing measures such as barrier tapes and gel filling, which are costly and sometimes degrade electrical performance. It is also worth noting that many of these waterproofing gels are petroleum based and are therefore unsuitable for use indoors (other than to a demarcation point), as they represent a fire risk. Indeed, the distance such cables can be run within a building is usually limited by national standards.

Further, the construction of the cable affects water ingress. Low-smoke zero-halogen (LSOH) cables tend to have a lower resistance to water ingress because the sheathing materials used are even more hygroscopic than PVC. FTP cables, with a longitudinal foil screen, have better resistance to water ingress as the screening material acts like a water barrier tape. However, it should be noted that FTP is still not waterproof.

Severity of Exposure The effect of water ingress is also dependent on where the water has been and for how long. Short-term exposure to the middle of a PVC cable run, with a small quantity of clean water, is unlikely to have any long-term deleterious effect. On the other hand, if LSOH cables lying directly on a concrete floor slab, with no containment or protection, are submerged for a week, then the risk of damage is much greater. Water containing dissolved contaminants from, for instance, a dusty screed floor, also represents a greater risk.

An even greater threat than the effects of water ingress through the cable sheath is posed by the open end of a cable being exposed to water. The tightly twisted pairs inside a data cable encourage a capillary action that can draw water significant distances into the cable, destroying the electrical characteristics. Cable affected in this way will nearly always have to be replaced.

  • Care to provide some references regarding PVC and your claim the form used on for cabling is hygroscopic? What you have written contradicts both my training and a lifetime of observation. – John Gardeniers Jan 18 '10 at 20:38
  • I actually asked my question because I found allusions to the fact that cat5 is water resistant but does allow water through, but I couldn't find any direct statements as to how or when it is water permeable. So, please if there are any direct citations as to water resistence in cat5, please include them. I'll even give a bounty for such a direct citation (ie from a cable vendor re water and plenum grade wires, or a standards body, etc). – chris Jan 19 '10 at 16:20
  • I don't think that PVC is considered hygroscopic. The original poster may have been confusing PVC with polyethylene (PET) or polycarbonate. Like all substances, PVC does transmit vapor -- which is why you generally run CAT5 outdoors in a pipe. If there are puddles or pools of water in the conduit, water vapor will eventually infiltrate the cable and damage it. From a practical POV, what does that mean for cable service life? Other than saying "its bad for the cable", I don't know. – duffbeer703 Apr 15 '10 at 2:56
  • @chris: This wikipedia article may help point you in the right direction. en.wikipedia.org/wiki/Moisture_vapor_transmission_rate – duffbeer703 Apr 15 '10 at 2:59

Depends on the conditions of the cables, where it got in ect, for example there would need to be openings in the insulation on the cat5 to do any major damage.

Since the passages are poorly ventilated apparently, there also comes into question a health risk with the growth of fungus and moulds.


I think to be quite honest cat 5e is not waterproof, hence why you have the option of using "exterior" grade cat5e..... I was always lead to believe that 5e was to be kept as dry as possible.... ok, the odd bit of moisture here and there is by no means going to have a serious effect on the stability of the cable within the PVC sheath. But 5e should be used indoors!


I would be more concerned about where the closets are located in the building and how well ventilated they are. Damp, poorly ventilated closets are a great place for mold to form. Mold is far worse of a threat than bad cables.

My recommendation to you is to get a public adjuster who has expertise in commercial fire and water-damage claims. It is going to be difficult for you as an IT person to establish that the cables are damaged or will fail over time. A public adjuster who does this for a living for people with insurance claims (vs. insurance companies trying to limit claims) will usually lead to a better outcome for you.


Water can affect fiber optic cables and splices if the water freezes, causing a macro-bend, which creates optical power loss.

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