I recently installed a bunch of low-voltage outdoor LED lighting in my front and back yards. I used two of these transformers (one in the front, one in the back) and fixtures like these. Two odd things happened that I’d like some expert advice on.
Issue 1. It rarely rains here in Vegas, but a week or two ago we had three or four days of nearly non-stop light rain. Not buckets, but pretty much constant for several days.
On one of those evenings I noticed that the lights in the backyard were out. I went out and checked the breaker that controls the outlet they’re plugged into, both mounted on the wall that separates our yard from the neighbor’s. The main breaker hadn’t tripped, but the GFCI breaker in the receptacle itself had. As I went to reset it, I got a shock. There was no exposed metal, just the plastic face of the receptacle.
The receptacle is a standard outdoor unit, with a nominally water-resistant cover, but when something (like my lights) is plugged into it, the cover can’t close, of course. So the face of the outlet was wet, and I suspect that the water conducted the current that shocked me. Once I reset it, the lights worked fine, and it stopped raining soon after and the problem hasn’t returned.
Do I need to replace the outlet? Did the shock I got indicate a faulty outlet, or was that to be expected when the face of the fixture was wet? I see I can get a box that is waterproof while in use, which seems like a good idea in this setting. I suppose replacing the outlet as well, only another $15 or so, couldn’t hurt. But is it necessary?
Issue 2. The other issue is not a safety concern, just a strange phenomenon I was hoping someone might explain. I strung 12 fixtures on a line from the 200-watt transformer. They were all LEDs, and none was more than 10 watts. The total was no more than 140 watts. So there was no question that I overloaded the transformer.
After I connected the 12th fixture, the six or seven fixtures farthest from the transformer all started flashing on and off together. I thought I had somehow damaged the transformer, perhaps by accidentally shorting the line at some point. But I switched the front and backyard transformers (identical) and the other one did the same thing.
Then I disconnected one fixture, and everything was fine. I reconnected it and disconnected a different one, to eliminate the possibility of a faulty fixture, and everything was still fine, as long as there were only 11 fixtures on the line.
I called Home Depot’s tech support line, and after stumping the first person was escalated up to “the electrician.” He said that you have to run 12 or more fixtures on two separate lines from the transformer. When I asked him for a more technical explanation, he said, “That’s just the way they are.” I don’t know if he thought I wouldn’t understand, or if he didn’t understand it himself. (I suspect the latter.)
But I’m sure there are electricians and engineers here who can explain it. What was happening?
I assume these transformers are designed for LED fixtures, since that’s most of what Home Depot sells these days. In my family room, I have an old low-voltage track light system that was installed before LEDs became available, and I found that when I replaced all the original halogen lamps with LEDs, they flashed, a lot like the ones outside did. Researching that, I found that some transformers need a minimum load, and the LEDs I was using didn’t meet that threshold. The solution was to keep one halogen lamp in the chain so that the total wattage was above a certain limit.
But the problem in the back yard wasn’t an underload like that, nor was it a wattage overload. It seemed to be a fixture overload. What’s the explanation?
Thanks.