Wire & Connectors 

The wire most commonly used in professional residential landscape lighting is #12 SPT cable. Although it is commonly called wire, it is actually cable because it is multi-strands of copper wire bound together. Wire is technically a single piece or strand of metal, commonly copper, however the term is used frequently to describe the cable used for landscape lighting.

The #12 refers to the diameter of the bundle of strands. In the US we use the American Wire Gauge (AWG) standard for measuring wire. The smaller the number, the larger the wire, so a #10 wire is larger in diameter and can carry a greater electrical load than a #12 wire. The SPT stands for Service Parallel Thermoplastic to describe the cable. This wire is also called zip cord. It is actually two separately insulated conductors that are bonded together. The insulation on one of the conductors is ribbed for polarity identification.

Other sizes are used as well. The wire attached to the fixture, called a pigtail, is often #16 or even #18. For longer wiring runs, #10 or even #8 may be used to reduce voltage drop or to handle a higher wattage load. However, for most residential situations #12 wire is the standard.

Stranded wire is preferred for landscape lighting because of its flexibility and greater current carrying capacity. Single strand wire uses the same AWG standard and is the most the commonly used wire for 120 volt line voltage in the home. Solid wire may be used in landscaping systems to carry line voltage to a direct burial transformer. (Remember, all line voltage installation should be performed by a licensed electrician.)

SPT cable must be marked with the UL listing, acceptable operating voltage and temperature, and that it is sunlight resistant before it should be used in any landscape lighting system.

When two or more cables are connected it is called a splice. In its simplest form a splice is could be the bare conductors of two cables twisted together, however this splice would not be very strong and could be pulled apart easily. It also would be exposed to the weather and possibly to another conductor. Both of these situations could lead to failure. To increase the strength and reduce exposure, a wide range of connectors have been invented over the years. Some of the most common are:

• Wire Nuts are available in several sizes to accommodate different wire sizes and combinations of wires. They are made with a plastic body that contains a wire spiral. The wire nut is slipped over the bare ends of the wires to be joined and twisted until secured tightly on the wires. Commonly used in line voltage wiring, wire nuts are not used widely for landscape wiring because they can be worked loose and do not provide complete protection from moisture. Although somewhat messy, these problems can be reduced by dipping the completed connection in Liquid Tape or silicone.
• Quick Connectors use corrosion resistant sharp prongs to pierce the insulation and complete the electrical connection. Although there are several designs, the two halves of the connector are screwed together to keep the wires in position and in contact with the piercing conductors. This type of connector is fast and does not require the service wire to be cut. However they are not moisture tight and should not be used below grade to reduce the chance of failure due to corrosion.
• Crimp-on Connectors are available in several styles including spade and bullet. One end of these connectors is crimped onto the bare conductor with a special set of pliers. The other end fits into a similar connector that is crimped onto the other conductor. The matching connectors are referred to as male and female types for somewhat obvious reasons. Crimp-on connectors have the advantages of being a strong connection that can easily be disconnected. Unless used with insulating shrink tubing they are not very resistant to corrosion.
• Silicone or epoxy filled wire nuts are specifically made for direct burial of splices. They are very resistant to corrosion, however they are messy.
• ACE direct burial cable connectors by Nightscaping® use a brass tube that is open on both ends. After the bare conductors are placed in the tube, they are secured with Allen screws. A section of insulating shrink tube is slipped over the connector and heated until it is tightly sealed. These connectors provide excellent strength and resistance to corrosion. They are expensive, but considering the cost of finding and replacing a failed connector, the price doesn’t seem too excessive.