Saturday, June 14, 2008

Irrigation Wire Problem

Mike K. from Atlanta asked:

Hi Craig. I bought your sprinkler repair DVD and I have really learned a lot. I'm now adding lawn sprinkler repair to my lawn maintenance business, and it's going great. My customers now love me even more! But I've got a problem.

I've got a sprinkler wiring problem that you don't cover in the DVD.

I have power at not working sprinkler valve number #4. I checked the resistance on the solenoid, and it read 26 ohms. When I check the power at the valve with the solenoid disconnected I get a reading of 27.8 volts. When I wrap the solenoid wires around the valve wires I get zero volts.
I thought maybe my meter was bad, so I borrowed the owners meter and the same thing happened. I told him that I would be back tomorrow to fix it. HELP!!!

Mike, I've got good news, and bad news. The good news: I know what the problem is. The bad news: it's not always easy to track down and repair.

What you are experiencing is called a "partial connection". This means that at some point in the circuit you have a wire connection, or a cracked wire, that is touching JUST ENOUGH to allow the ohm meter to send a tiny signal of power through it. This is why you can read a good valve at the controller, and get a sufficient power reading on the disconnected wires at the valve.

However, once you attach a "load", meaning resistance like the copper coils that constitute a valve solenoid problem, the power will fall off.

This is because the electrical path that the volts follow is constricted by the small amount of conductivity that the bad splice or cracked wire is allowing.

If this sounds confusing, check out the power points in the member section of That will make understanding it easier.

Now on to the bad news. The "electrical constriction" or "partial connection" could be anywhere along the wire path. Did the contractor run out of wire before zone #4 and splice in 6 feet of wire to reach the valve? 36 feet? Did someone planting a tree or installing a fence five years ago make a splice that went bad?

Don't give up hope yet! Here are some common places to look.

1. Is the #4 connection good in the controller? Grab it and give it a wiggle.
2. Is there a splice box beneath the controller? Thats the second thing to check for.
3. Have you used a wire finder to locate valve boxes in the yard? There may be splices in the boxes.
4.Look in the first valve box electrically upstream. Bad common? Weird common wire split?

Worst comes to worst, run a new wire or install a doubler. I show how to do that at my sprinkler repair site

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