I think I have a situation where the wire that's in place has been compromised, but wanted some input on this in case anyone else has had a similar experience.

Everything is in conduit (which is wet now), but they didn't use direct burial wire - it's just plain ol' cat6. This is for gate control, and the cat6 has been turned into a 2-conductor by twisting solids together and stripes together, per manufacturer recommendations.

What we're working with is Mobotix MX2Wire transmitter/receiver sets with T25 camera/keypads at far end. There are 2 identical setups on the run, the first being about 350' from the house, and the other being about 350' further along. The junction box at the side of the house is about 200' from the equipment room, so we're looking at runs that are a total of about 550' and 900'. These have been working well for the last 3 years, and this year they both died at about the same time. I replaced one transmitter set and got the closer station back up and running, but the farther station isn't coming around - and I've tried everything at this point.

I brought the parts that seemed to be dead back to the shop and was going to try to get RMAs for them, but decided to test them there, and they worked. I used a different PoE injector for this, since the ones on site are installed in a rack, and I thought I found the problem. So I figured I'd try to replicate their real world environment by wiring in a spool of wire and they worked right away. I ran these things over 1000' of 22-2 and they're solid.

So it LOOKED like it was a power issue. So I brought out the PoE injectors I used at the shop and...nada. The only thing left is the wire thats in the ground, soaked. We're in our rainy season now, and it rains like crazy every day, so that does seem to make sense. I tested the wire for shorts and continuity and it seems OK, but once you put power on it, nothing gets through.

Sorry that's a long one, but I *think* I can declare this wire NFG. Any input is appreciated! Thanks

This is why the NEC states that conduit, when installed outdoors, or buried underground, it is considered a wet location. Therefore the wire or cable inside the conduit has to be listed for wet locations.

It's considered a wet location because:

1. It can leak at any of the couplings.

2. It can fill with water from condensation.

Is there any way you can pull out the Cat6 and use it as a pull string to pull new (wet location rated) wire?

Found this. [Link: fmsystems-inc.com]

If it's not the cable creating the problem right now, it's only a matter of time before it becomes a problem.

My experience is that standard CAT cable in this area will last 3-5 years in underground conduit before it fails.

Timing sounds about right for your wire to go bad...

Consider replacing with fiber and appropriate interfaces?

Have you checked the wire to see if it has shorted or open? That's where I would start- in either case, I would also connect a TDR and find out how far from the ends it has a problem.

What kind of conduit- metallic, plastic or liquid-tight?

Thanks for the replies guys.

David - it wouldn't be easy but it probably could be done.

Burton - Thanks for that - that's a good read and an interesting device.

SB - I agree, I wish I was around when the wire was put in. We're actually at about the 6 year mark since the place was built so I guess it would be due for a re-do of the cable in the ground.

Fred - I've used those before but there's no easy way to get power to the pedestal where the station is. I'm going out there now, and I'll take a look at it with that in mind.

Highfigh - I did exactly that and everything seemed to be OK. Brought the parts back to the shop to bench test and really only found one thing to be a bit off. I called tech support and they said that thought the run was too long, never mind the fact the things been working for years now.

The conduit is plastic. Again, wish I was there when it went in.

I'm in no way saying that plane jane CAT cable within a conduit is a good idea, but hell, there's plenty of places in New England where this exact setup/wire has been used for years and years without issues. Just walked a job the other day where they had 24 Cat5 cables within a plastic conduit, between buildings, for the past 18 years without issue.

My guess would be critters have chewed the cable to a point where you are getting intermittent connectivity or exposed wires within the water.

Sounds like a new cable is going to be needed to get this working again if the devices aren't faulty.

Did you use a TDR? It may not be shorted, but if your meter didn't see a short, it may have seen open because it was looking at the circuitry of the device, so it should be set to measure a Diode.

If the cable has moisture in it, it's probably not creating a pure short or open condition, but is causing some conductivity between wires which is creating the problem. 

But it should show up on a meter.

I hope the conduit has some kind of fitting every 50' for making it easy to pull cable because without, it kinda sucks.

Have you ever measured the voltage on a power supply(or battery) and it appears to be correct
then plug it in and it does not work?

The line is not showing a direct or maybe even a high resistance short
until a load is applied

You need a better test or meter

A DUT "Device Under Test" used to verify
the physical properties of the cable have failed

[Link: weetech.de]

Note that a "short" is zero ohms of resistance.

There is no such thing as a high resistance short.

Everybody's first lesson in discussing electrical should be that shorts are wires connected together that should not be connected together. Wires that should be connected together, that aren't, are called an open, short for open circuit

When testing for shorts and opens, FIRST check for voltage across the wires. If you get a zero ohm wire to wire situation, that's a short. An almost short with some resistance is very possible, too. Also, one conductor shorted to ground can be a problem even if the two main wires have the right resistance to one another. There must also be the right resistance from each wire to ground.

Sure- plenty of times- it indicates that the power supply is weak, a connection is bad or maybe hte regulator is bad, assuming it's a regulated supply. That's a good example of voltage, but nothing to back it up- it's like measuring the water pressure in a garden hose after closing the sprayer and then closing the supply valve- the pressure is still there, but as soon as you open the sprayer, it decreases and goes away.

So, use a megger or a battery and an incandescent bulb if you already assumed the wire is bad- that way, if it smokes, it's academic.