Well, I may be a bit late to ask this since I already ran the wiring and installed all the lights, but anyway, here’s the dilemma. I am installing a light fixture on top of each post on my deck railing. There are a total of ten posts, hence ten lights. Each fixture has three 12v light bulbs. Each light bulb is 18watt, push-turn (bayonette base, like car tail light bulbs), so each fixture is 54 watts. I ran 14 gauge solid romex (2 conductor plus ground), from the transformer and daisy-chained to each fixture. In other words, all fixtures are wired in series. I was carefull to observe the polarity at all fixtures. Since total wattage is 540watts, I installed a 600 watt 110v-to-12v transformer to an outside GFCI outlet and connected the wire from the fixtures to the terminals on the transformer. When I flipped the switch to energize the GFCI, all the lights worked but the bulbs are of different brightness: the fixture that is first in the series, or closest to the transformer was very bright, but the brightness of each subsequent fixture is stepped down, and in the last fixture the filament in the bulbs barely glows. Reversing the polarity at the transformer makes no difference. Any thoughts??? In reply to a comment by Les. When I said "fixtures are wired in series", I meant daisy-chain, as in the way several outlet receptacles are wired together in one room. Is that what you call wired in parallel? if so, my mistake. And yes, when I remove the first fixture (or any other), all the others still light up and I get the same step down in brightness, where the first one is the brightest light then they get dimmer and dimmer down the line. My original thought for this dimming feature was because the solid wire could make it harder for the transformer to push the low voltage throughout the entire length of the wire (about 60ft.). Is this a correct assumption? Or does stranded or solid make any difference? Also, I used romex because I had several rolls left over from building the house and I pushed it through pvc pipe and it’s all under the deck, nothing exposed, so no worries there. Another idea I had was to remove the transformer and just push 110v through the wires by using a dimmer switch and push very little current to see what happens. Will the 12v bulbs blow out if I set the dimmer at the lowest setting? I have read that bulbs don’t care if the current that is ran is either AC or DC.
The romex insulation and rubber jacket will deteriorate from being exposed to UV rays, and There is no need to use wire that big on low voltage wiring
The wire isn’t going to wake the difference. Stranded wire is used in installations where movement is required – it can flex or more without breaking – like the cord on an appliance. Solid is used where movement is not required.
If some are dim I’m suspicious of your grounding, If DC lights are not grounded properly they may be dimmer.
Probably should have used stranded landscape wire. It’s cheaper than Romex and it won’t break down as quickly in extreme conditions, which I fear Romex will eventually do unless they’re in a conduit.
As for your brightness issues, try running in parallel instead. You really don’t want series. Take the lamp out of the first fixture in the line. Do the rest go out? If so, you’re in series and the same thing will happen if a lamp burns out.
As far as I know, most 12 volt landscape lights are not individually grounded so that shouldn’t be your problem. Your transformer should have a ground and that is worth looking in to but I doubt it’s your problem.
—EDIT—
The problem may lie with using too big of wire. Seems that most landscape lighting wire is around 18AWG. You might want to check with a landscape lighting company to find out. If all else fails, you could run down to your local home center like Lowe’s. If you’re lucky, they will have their "electrical pro" working and he/she can assess your problem. Could be that you’re experiencing voltage drop due to the larger wire size and potential long distance wire runs. If so, you need a bigger transformer. Your lighting may be asking for more than the 600w transformer output when factoring in things like wire size and voltage drop (DC is bad about this).
The dimmer thing doesn’t sound like it would work. I work with theatrical dimmers and they push close to 120v even at the lowest settings (since they chop off part of the waveform to produce a lower average voltage without actually dropping the voltage). You’d also have a fire hazard if that dimmer somehow got bumped up to full (if it did work).
I suggest calling a landscape architect/lighting designer on this one. Good luck!
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The problem is you used to small of wiring! Of course you should never use romex wire outside. The voltage drop is given by (watts*wire length in ft)/wire constant. For 14 gauge wire the constant is about 3500. Other constants are 12 gauge – 7500, 10 gauge – 11900. Lets say you have an average of 30 feet of wire for 540 watts then you have about 4.6 volts drop. Way to much. You should never daisy chain landscape wiring. Use a zoned system with several nodes. Then use the appropriate voltage tap from your transformer for each zone. Many time I will use 10 gauge wiring to reduce line loss. Of course LED lights are better since they have high lumens/watts ratio.
Lastly measure the current using proper VOM and do not exceed the nameplate current.
I would have used #12 or #10 run in a loop, i.e. power is feed from both ends. Think of it like this: Your voltage at the transformer is like water pressure at the water tower. Your wire is like pipes and the pressure loss in your pipes correspods to the voltage loss in your wire. The bigger your pipes and the shorter your pipe runs, the less pressure loss per foot of pipe; same with wire. And just like electricity, the smaller your pipes, the more water has to push thru the pipes and the velocity is increased and your pressure loss per foot is increased. And just like electricity, every time your water velocity increases by a factor of 2, your pressure loss per foot increases by a factor of 4!!! What you need to do is this: 1. Loop your wire run. 2. Increase the size or your wire.
Hey there. Did you find a solution to your problem? I am having the exact same problem on some indoor 12V puck lights. I have 13 of them (20 W) running on a 300W transformer. All are interconnected w/ 12/2 Romex (in wall wiring). I get somewhat bright in the first light, then it gets progressively worse along the line. Curious as to what your solution was. Thanks!
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