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steveparrott
04-19-2010, 07:22 AM
The recent troubleshooting thread was a good brain teaser - also educational.

Would anyone else like to share weird system failure stories and how you solved the problem?

Pro-Scapes
04-19-2010, 07:42 AM
Still unexplained but working fine now.

http://www.lawnsite.com/showthread.php?t=255505

http://www.lawnsite.com/showthread.php?t=281464

steveparrott
04-19-2010, 08:32 AM
See if you can solve this problem. This stumped us for awhile. Double kudos to the first one to name the cause and solution. (This one is good to know, and might change the way you do things.)

A system with about 30 fixtures, 7 home run wires to a 1200W transformer. The system operates normally, however, if one of the common breakers was switched off, the lights on that common did not turn off - they glowed, and measured 5 volts at each of the fixtures. Why?

Gr1ffin
04-19-2010, 08:38 AM
(erased my guess... I'll leave it for others)

RLI Electric
04-19-2010, 09:12 AM
Steve, I think you have a short to ground. If you could gfci the secondary side it would have tripped (see earlier posts about that). To isolate that you would go to the goofy run and take a fixture offline. The fact that all of them are doing it on that particular homerun may mean that the short is in the actual homerun itself. That is my guess.

steveparrott
04-19-2010, 09:30 AM
Steve, I think you have a short to ground. If you could gfci the secondary side it would have tripped (see earlier posts about that). To isolate that you would go to the goofy run and take a fixture offline. The fact that all of them are doing it on that particular homerun may mean that the short is in the actual homerun itself. That is my guess.

Bob, it could have been that but it wasn't. No shorts, no malfunctions. The cause really surprised us. Any other takers?

RLI Electric
04-19-2010, 09:34 AM
Reversed polarity on one of the fixtures?

irrig8r
04-19-2010, 10:23 AM
Voltage crossing from one cable close to another through thin or nicked insulation where they share close quarters in the transformer?

Weak inductive load from the transformer coil passing to the home run cables?

steveparrott
04-19-2010, 10:57 AM
No winners yet. A clue - the suspect common was shared by two wire runs. Switching one of the runs to another common solved the problem.

The Lighting Geek
04-19-2010, 12:37 PM
the commons were connected to 12v by accident?

steveparrott
04-19-2010, 12:53 PM
See if you can solve this problem. This stumped us for awhile. Double kudos to the first one to name the cause and solution. (This one is good to know, and might change the way you do things.)

A system with about 30 fixtures, 7 home run wires to a 1200W transformer. The system operates normally, however, if one of the common breakers was switched off, the lights on that common did not turn off - they glowed, and measured 5 volts at each of the fixtures. Why?

Here's what happened.

Two wire runs shared the same common. One run was connected to the 12V tap; the other run was connected to the 17V tap. When you turned off that common breaker, a current was created due to the differential between the two taps - hence a 5V current going to the fixtures.

I don't understand why this happens (maybe an electrical engineer can chime in) but it does.

For this reason, it's a good practice to distribute wire runs to commons based on voltage taps used. For example, all 12V runs on one common; all 17V runs on another common, and so on.

emby
04-19-2010, 03:52 PM
I find this very interesting. Kinda like your dryer or stove using the neautral for the unbalanced load. Going to do some reading later tonight in my old electrical theory books.
12 Volt is a different beast though.

Ken

Pro-Scapes
04-19-2010, 06:24 PM
Why wouldn't it show voltage ? When you switch off the common your breaking the link between the common on the core and the run. Your tap essentially becomes a connector joining these 2 runs together.

Since your still feeding 17v down one run... its flowing back to the common tap that is OFF but still finding a path to complete its journey although the path it is taking is a long one through an entire separate run. I would have actually chimed in with the guess that you had a disconnected common inside the transformer. I ran into a very similar scenario with a transformer where the spade terminal behind the common breaker was disconnected. With no load I was getting a reading of 30v on a 12v tap.

I wonder if that 5v is due to the difference between 12 and 17v. It could be due the to extra load instead since you are basically creating a variation of a daisy chain ?