Low voltage power must be supplied to landscape lighting fixtures and lamps for them to function properly. Low voltage cable delivers this power from transformers to light sources.
Low voltage cable for landscape lighting is generally a 2-conductor cable.
This cable is suitable for direct-bury installations and comes in a variety of gauges. The lower the number on the gauge of cable, the thicker the cable is going to be. Thicker cables can carry the power further than others. They also have higher amp rating capacity.
Each cable size also has its individual cable constant number. This number will be used when a contractor performs a voltage drop calculation.
Use cables that meet industry standards, like UL 1493: Underground Low-Energy Circuit Cable and CSA Standards C22.2.
Stripping cable.
You should own a good quality pair of cable strippers. Be sure not to cut any other type of cable other than copper with them. Cutting other types of cable, like bailing wire, can dull the blade. When you strip the insulation from the cable, be sure not to cut through any of the strands. If it frays, a 12/2 cable can become 16/2 at the splice point. This could cause heat at the splice and a potential fire.
Connecting cable to a transformer.
It is important to review the manufacturer’s specifications on the transformer terminal block size. Generally, terminal sizes accept multiple cables. When you insert cables into the terminal blocks, make sure the strands of the cable are twisted and not fraying. If frayed wires touch from one block to another, it could cause a fire. Tighten the terminal screw until it is snug. Grab onto the cable and pull down and rotate it clockwise. Tighten the terminal screw to ensure the cable will not slip out. This practice will provide a solid mechanical connection.
Burying cable.
The National Electric Code requires landscape lighting cable to be buried 6 inches below the surface of the ground. It is recommended that cable be installed 8 inches to 12 inches deep in a lawn area. Keep all cable away from any lawn edge or planter edge, as it could easily be cut by an edging machine. Cable installation in flower gardens or planting beds should be 8 inches to 12 inches below ground and inside a PVC conduit. This provides extra protection against any excavation being performed.
Installation in trees.
Cable runs in trees should be made with proper hardware. Always use stainless steel fasteners on trees. Do not use copper or brass screws due to their toxicity to the tree. Never attach cable to a tree with staples or any mounting hardware that can choke the tree. Install cable to a tree at least ¾ inch off the trunk or branches to create a gap. The cable should be secure but retain enough slack to move during lighting maintenance service.
Cable connections.
We all have our favorite cable connection. Any connection that is directly buried should be made for landscape light and protected with some type of approved waterproofing. Select a connection and follow all manufacturer specifications for cable combinations.
Round SO cable connections.
Underwater lights, as well as many brands of low voltage bistro string lights, require special attention when connecting to standard landscape lighting cable. SO cable is a round 2 or 3 conductor cable that is used on most underwater lights and low voltage bistro strings.
The inside of the SO cable generally contains a paper or nylon conductor separator. This can act as a wick and draw moisture into the main jacket. When joining the SO cable to landscape lighting cable, it is important to seal off the round end of the cord to prevent any water wicking. This can be done with a piece of resin-filled heat shrink. Some manufacturers offer waterproof junction boxes or IP68 compression connections to create this special splice.
Sizing cable and installing it properly allows you to engineer a true lighting system, and one that will provide a trouble-free environment for years to come. Do it right and the referrals will follow.
Low Voltage Logic by Kevin Smith, National Technical Support and Trainer at Brilliance, was originally published in the October 2021 Issue of Irrigation & Green Industry. Visit igin.com for more information about Irrigation & Green Magazine.
