What gauge wire Malibu lights

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Old 09-12-08, 07:03 PM
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What gauge wire Malibu lights

Have some small outside lights from Malibu and need to run another light. What is the gauge wire I'd need. Also need to run some led "rope lights" for accent lighting. Would that be the same gauge wire?
 
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Old 09-12-08, 07:59 PM
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The gauge depends on the load and length of the run. Since this is hard for the average person to understand and calculate they often just use examples. The zip cord wiring comes in #10 through #16 wire sizes I believe. Most small 30 foot total length, 60-100 watt systems use #16 as you add lights and length you would increase wire size. Nothing says you cannot use a larger wire size on a smaller system. You may decide to add light or extend its length and you would have to dig the wire up and change it if it were to small.

I have tons of outdoor lighting and in some cases I actually use romex electrical cable to make runs. I also found that the cheap push on connections that most lights use are really a weak point. I often cut them off, strip the wires back and use standard wirenuts to make the connections. This is low voltage you do not have to worry about water except for corrosion and as long as you use copper, which all the wire is, it should be OK.

Many of the systems actually depend on the wire reducing the voltage somewhat. They will tell you not to put a light in the first 10 feet or so of run from the transformer. While this is inefficient the bulbs do last longer so you might want to consider voltage drop not such a bad thing. These bulbs are expensive and do burn out rather fast at elevated voltages. Roughly speaking putting 10% more voltage on a bulb gives it 10 times less life and 10% less gives it 10 times more.

To calculate load... watts are amps * voltage. We know the voltage is roughly 12 volts. So a 20 watt bulb draws about 1.7 amps. If you had a set of 8 that would be (rounded) about 14 amps. In reality it would be somewhat less dues to losses in the wire and transformer but in this case you would use a (recommended) minimum of #14 wire. If you has a set of 12 it would be 20.4 amps and at least #12 should be used. If the runs are long, over 30 feet, you would want to go to a larger size to maintain the voltage. You will see this when you have a long run and the last few lights are dimmer. You can also split the runs so only 4 lights are on each of 2 runs, etc.
 

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Old 09-12-08, 08:50 PM
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Also need to run some led "rope lights" for accent lighting. Would that be the same gauge wire?
What voltage are they? Most ropelights I have seen are 120v. Malibu type wire would not be suitable.
 
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Old 09-12-08, 10:48 PM
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Rule of thumb for low voltage systems: The heaviest cable is used nearest the transformer because it carries the highest load, which is all of the lights. As you get further down the line, the lights that are upstream don't come into play, so you can use lighter gauge cable. If you're adding only one Malibu to the end of the line at a reasonable distance from the previous light, 16 gauge should work fine.

Make sure the transformer won't be overloaded. Most are rated in watts. Add up the wattage of all of the lamps on the transformer -- including the new light -- and make sure you have at least 10% headroom.

Anal retentives like me like to allow for 20% headroom, which means 80 watts on a 100-watt transformer. I don't like it when transformers run hot.

You can't run any of the common rope lights you'll find at the local big box store on a Malibu circuit, and you can't use its cables or bury an extension cord. Powering 120-volt AC rope lights outdoors is a whole different subject.
 
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