Ok, I'm replacing the ground lighting in my yard and have a situation I'm
having difficulty troubleshooting. Here goes:
I have approximately 30 fixtures, each with 20-watt bulbs (little quartz
jobbies). I have a new 600 watt, 12volt AC transformer. I've run mostly
new wire (some old stretches where it goes under concrete walks, etc. The
fixtures are soldered in, not attached with the cheap clips. The total run
is about 100 feet.
My previous system used a 300-watt transformer, but had only half as many
lights and most of them were broken from years of being bumped by the
lawnmower, tripped over by the kids, etc. At the end, only about half were
The power feed goes underground in conduit to my basement, where it's on a
dedicated GFI circuit.
When I got everything in place and switched it on for the first time, the
bulbs were bright near the source, and got dimmer, the farther away from the
transformer you got. Towards the end of the line, the bulbs didn't light at
If I test the voltage at output side of the transformer, I get 11.4v. If I
take out all of the bulbs, and test the voltage at the end of the run, I get
11.3 / 11.4 v. If I test any fixture (with no bulbs in anywhere), I get
For the next test, I put a voltmeter on fixture #5 (I'll number them
sequentially starting with the one nearest the transformer as #1) and
removed all of the bulbs. At the start, I showed 11.4v. If I put a bulb in
fixture #1, my meter on fixture #5 drops to 11.0v. If I take the bulb out
of fixture #1 and put it in fixture #2, my meter on fixture #5 drops to
10.6v. If I put the bulb in fixture #3, the meter drops to 9.8v. If I put
the bulb in fixture #4, the meter drops to 9.5v. I've checked and rechecked
all connections and voltage at the transformer. I've used different bulbs
without changing the result.
For the next test, I leave the meter on fixture #5 and put bulbs
sequentially in the first 4 fixtures.
With a bulb in just fixture #1, I get 11.0v on the meter on fixture 5. If I
put bulbs in both fixtures #1 and #2, the meter drops to 10.3v. Bulbs in
1,2 & 3 = meter drops to 8.8v. Bulbs in 1,2,3 & 4, meter drops to 7.0v.
You can see the bulbs are dimmer as you go from 1 to 4.
I also measured the voltage at the input side of the transformer as I placed
bulbs in the fixtures. I start at 118.0 volts, and drop to 117.9 as I
insert the first bulb - then it recovers to 118.0. If I put bulbs in
fixtures 1 and 2, then the input voltage drops to between 117.8 and 117.9,
but recovers after a few seconds to 118.0.
I've taken apart one of the fixtures to check for shorts and find none.
I've checked an un-powered (and temporarily unhooked) fixture with an
ohmmeter with and without a bulb inserted. Everything looks normal. I've
tried temporarily hooking everything to the old 300w transformer and using
only the first 5 fixtures, but I get the same result!?!
I think I've eliminated everything BUT the feed line from the house. None
of the tests has tripped the GFI breaker, but maybe it's bad anyway?
Is there something I'm missing? These are all wired in parallel, so there
shouldn't be ANY drop in voltage when you insert the bulbs. I'd really
appreciate your help.
Any idea what is going on here?