So half of my sprinklers aren't working and I've diagnosed the problem that the valves that are affected are not receiving a full 24 volts, rather only 17-18 volts.  I have isolated the general location of the wire run where it is affected, but the entire length to check would be nearly 100 feet.  I would have to dig up the entire line to check it. It would be easier to run a new low voltage line, but if possible I would like to use the existing line that is already buried.  If I knew the exact spot where the line is affected I have no problem digging it up to check it out, but I don't know where that is.  Is there any tool that could tell me the general area of the problem?

Edit: See updated post for resolution.

http://www.rainbird.com/landscape/products/controllers/TBOScontroller.htm

Sounds like a real headache. I don't know of any tool that will help in that situation. Try to avoid running wire that far, if at all possible.

We use a wire tracer or "lost valve locator" to trace wires or specifically to find lost valves, or breaks in the wire.
Something like this:
Valve locator

You may be able to rent one from a sprinkler parts supplier that deals with Contractors.  Buying a unit will be about $500 to $700.

Another alternative is to hire a sprinkler contractor to come out and trace the line for you.  

Another alternative is to convert the problem station(s) to a stand alone controller like the one linked previously or the Hunter version.  The downside to the Rainbird or Hunter standalone is you have to use the corresponding company's valve  since these standalone controllers also use special solenoids for the valves.

Wow. A voltage drop sounds more like a compromised(scratched insulation in the middle or an improperly sealed connection at an end leading to corrosion of the wire or connector) line or something broken in the system, a cut line would have been easier to find. This sounds more like either inspecting the entire length(I would start with the individual connections to make sure there isn't a loose or corroded connection somewhere, I don't know much about sprinklers so I don't know how these things are hooked up exactly), or just replacing everything to make sure it's all good and making sure everything is sealed up properly on the new wire connections. If it was just a cut line you coulda borrowed a TDR from a rich friend

Problem resolved.

I did indeed forget I had a simple toner for network cabling and I gave it a try but it isn't the best around.  One problem is that the tone being radiated from the generator can only be heard within maybe 2 feet of open space of the wire.  Once its underground and a lot of compacted dirt is on top of it, I couldn't locate any tone at all.  So yeah, I need a much better toner.

So how did I resolve it?  Long story short, I had unused wires on my line and switched to one of them.  The main problem was the common wire itself which caused all the valves to fail, but I did notice a similar problem with one of the valves specifically (the zone wire on the controller), so I also switched it to another wire.

Well like I said before I noticed a voltage drop.  The next thing I did after posting this thread was I ohmed out each line.  Now obviously my multimeter doesn't stretch 100 feet, but I had an extension cord that long.  I just got some alligator clips and clipped one end to the wire in question to the ground on the extension cord.  My multimeter at the valve station was touched to the same wire at that end and then the ground on the extension cord.  Some wires came through ok, but that common wire did not.  Had around 1.5 megaohms showing on that wire.  It didn't help locate where the problem was but it did help diagnose the problem.

For the life of me I cannot figure out what would have caused this except maybe corrosion.  The house is 40 years old and that stuff has been here longer than we've been the owners so I guess corrosion is a possibility.  I also suppose at some point in the future I should expect this to happen to the other wires.

The moral of this story:  If you are installing a new sprinkler system or replacing wire in an existing one, use wire with the most number of conductors even if you won't use them all.  Or if you will use them all, then put a second sprinkler wire in there with it just not connected to anything.  Sprinkler wire is pretty cheap so this gives you an easy fix if you are ever in a similar situation.

or just run it in plastic conduit so you can replace it.. cost you what? 20 bucks or so for 100' or gray conduit.

Bingo. Corrosion is almost always the answer if the wire isn't cut and the connectors are intact and connected properly. And it can happen pretty fast in the right conditions.



Now as I said before, sprinklers aren't something I've ever had to deal with - are sprinkler system wires direct-bury? If so, I'd say put them in a small conduit so you can replace them easily(not to mention probe for the location of the line without cutting the wire accidentally). 40+ years is pretty good lifespan for something of that sort I'd say. And if the wire itself was indeed corroded, multi-conductor wire may not save you depending on what the cause of the problem was.



 

This is a better idea, but I wouldn't want to remove the existing wire; what a pain in the ass that would be.  I suppose one could just forget it and install a new run in the conduit.

When I was doing designs, I would try to locate the valve manifold as close to the controller as possible for exactly these reasons. It amazed me how many installers would put valves all over the place, creating a frustrating puzzle of pipe and wire for the homeowner to solve when something inevitably broke. Another thing I hated was DIY manifolds that had to be completely torn apart to replace a valve or something.

Use these instead, they're awesome.