Low Voltage Cable

By Constantine Pergantis, Nite Lites, North Potomac, MD

This edition of Bright Ideas focuses on cable for low-voltage lighting systems. Cable is the lifeline of any lighting system. The correct size of the wire and distance it runs from the transformer will significantly affect the light output.

Question 1: Running wire from the transformer

Question 2: Type of cable

Question 3: Burying cable


Question 1: How far can I run wire from the transformer?

Pergantis: All wire resists electric current to a degree. This resistance limits the length of wire you can use. The gauge of the wire also influences how far power travels. Heavier gauge or multi-conductor wire can be used to permit longer runs from the trans-former.

Many charts have been made to assist the installer in determining proper cable lengths. A good guide is:

Gauge/No. of Conductors Safe Length
14/2
60 feet
12/2
100 feet
12/3
200 feet
10/2
150 feet

* LENGTH CAN BE INCREASED AS WATTAGE IS REDUCED.

The number of fixtures/watts on the system and voltage entering the cable from the transformer will have an effect on the last light. To compensate for stretching the distances, try to locate the controller in the middle of two short runs instead of at the end of one long run. If at all possible, try to make a loop with the cable (one piece of cable with both ends attached to the transformer).


Question 2: What type of cable should I use?

Pergantis: It sounds like a commercial, but make sure the cable is clearly marked as UL listed. Stranded wire is preferable to solid copper wire. Stranded wire is more flexible, easier to install, and allows easier fixture connections.

The thickness and content of the insulation can vary. Look for UV stabilized insulation with a rating of SPT 1, 2 or 3. SPT 3 is the thickest and will protect wire from accidental cuts during installation better than thinner versions.


Question 3: How far must the cable be buried?

Pergantis: Because the cable is for low voltage only, it does not have to be buried or protected by conduit. It can be laid on top of the ground, buried under mulch or soil, or even run through water.

It is wise to place the cable in conduit in locations where maintenance equipment can damage it. Put the wire in 3/4-inch PVC where it goes under sidewalks, turf, mulched plant beds and/or any place an edger or trimmer is likely to be used. This will help you reduce callbacks caused by overzealous edges operators.



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