Further distance with LED outdoor lighting?

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  #1  
Old 02-20-14, 11:40 AM
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Further distance with LED outdoor lighting?

What size direct bury cable do I need to run LED lights all around my house? I have LED Christmas lights that claim to be safe at over 1000ft in a series, so I have a feeling the traditional calculations are overkill for low wattage LED lights.

I plan on using #14 cable for two 300ft runs from a 300W 12VAC power supply, with about 50W on each run (Edit: i.e. 20 yard lights not xmas lights). It would be nice to know if in fact I will get hardly any light at the end of 300ft and what the real max is if I invest in large amounts of #14.
 
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Old 02-20-14, 04:06 PM
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Fifty watts worth of LED's at a distance of 300 feet intended for and fed by a low voltage (here, 12 volt) source is a traditional calculation, not a modernistic flea power calculation.

You're pulling a tad over 4 amperes. You want to lose no more than 5% of the voltage (0.6 volts round trip) to voltage drop.

Wire resistance may be no more than 0.6 divided by 4.2 (lost volts divided by amperes drawn) or 0.15 ohm.

.For the 600' round trip you need 4 gauge copper wire.

Scrub the project and redo it using a 120 volt feed out to the lights and a step down transformer out there for each of the 12 volt light clusters. For 50 watts the current will be 0.42 amps instead of 4.2 amps For this you can theoretcially use 22 gauge wire. However the minimum size for 120 volt household circuits is 14 gauge wire so go ahead and use that. The 14 gauge wire will let you expand up to 500 watts at each cluster.
 

Last edited by AllanJ; 02-20-14 at 04:26 PM.
  #3  
Old 02-20-14, 05:23 PM
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So it's the low voltage that's the difference. Christmas lights are 120V. Thanks for the info!
 
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