Outdoor Lighting

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  #1  
Old 08-15-10, 08:46 PM
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Outdoor Lighting

I have a simple question regarding low voltage lighting for our backyard. I have a stretch of about 250 ft. that has twelve 20 or 25 W fixtures (with a 400W transformer) and the lights on the end are very weak. I am going to switch to a variable voltage transformer and run three different lines with 10, 12, and 14 gauge cable to different parts of stretch that I'm lighting. I've read that it's best to tee off each line - run it to the center of where that line's lights are and then have half go one direction and other half go the other direction.

My question is - what is the best way to tee them off? Do I just make two connections on each + and - line?
 
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Old 08-15-10, 09:44 PM
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What gauge wire are you now using? 250' is a long run for low voltage so the lower gauge number (thicker wire) that you use, the lower the voltage drop over your run.
 
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Old 08-15-10, 10:05 PM
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I'm only use 12 G wire now.
 
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Old 08-16-10, 10:02 AM
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That's a pretty decent amount of DC amperage you are running. Here are the voltage drops over 250 feet for various copper wire sizes. I imagine that wire larger than 10ga will be cost prohibitive.

12ga 8.1%
10ga 5.1%
8ga 3.2%
6ga 2%

Is there any way you can locate your transformer near the center of the string of lights? That would cut the amperage and low voltage wire length in half and really help.
 
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Old 08-16-10, 05:57 PM
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I never thought about that (although it seems pretty obvious now). This is the way my system is setup now: The transformed is wired to my pool controller so that we can turn on/off the lights from our pool-side controls of from inside the house. From the transformer, there is a 250ft run of low voltage cable with the first light at around 50ft and the last light at the end (250ft).

Your suggestion would be to put the transformer at the 150ft spot and then have a 100ft run of low voltage cable in either direction so that no light would be more than 100ft from the source.

Three questions:
1. Can I use my existing 400W transformer and run both 100ft lines off of it without a drop in voltage at the end of the lines?
2. What gauge wire should I use if I have six 25W lights on each 100ft line?
3. The 120V electrical cable from my pool controller to the transformer (about 150ft of cable) would need to run under cement (should be Ok because I have a conduit line plumbed there already) and then the rest of the way through our planter beds. Is it safe to use the grey conduit buried a few inches underground for the 120V line?
 
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Old 08-16-10, 07:03 PM
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Is it safe to use the gray conduit buried a few inches underground for the 120V line?
Assuming a non GFCI breaker minimum conduit depth using THWN in conduit is 18" If you use UF you should use conduit for only short lengths where it enters and leaves the ground. The UF must be buried 24" minimum. If you use a GFCI breaker and circuit is 120v and no more then 20a you may bury the conduit one foot deep.

Note: in no case can extension cords be used for this purpose. You might want to buy the book Wiring Simplfied available at Home Depot or Amazon before going further and read up on wiring requirements. Electrical questions are best posted at Electrical - A/C & D/C - DoItYourself.com Community Forums
 
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Old 08-17-10, 04:53 AM
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How you described installing sounds good. Your existing 12ga low voltage wiring should work well. With the transformer in the middle you will have two runs of about 100-125 feet with six lights on each. I would definitely protect anything outside or near water with a GFCI. They are so inexpensive it's almost a no-brainer to use them.
 
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Old 08-17-10, 07:27 AM
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I would definitely protect anything outside or near water with a GFCI. They are so inexpensive it's almost a no-brainer to use them.
Actually it is a code violation to not use GFCI protection.
 
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