Ground Wiring Types

Split - T: The split-T wiring method represents two straight runs of wire that are connected to a T-junction, which is then connected to the transformer. This allows for more equal distribution of power to the center of a run, or to a run some distance away. The cable running from the transformer should be of a heavier gauge (8-10 gauge) than the two cables the fixtures on which the fixtures will be installed.

Loop: The loop method is similar to the straight method, except there is an extra length of wire connecting the last fixture in the run back to the transformer. Since voltage drop is coming from both sides of the run, it will produce a more uniform light output. It is important that you connect the same wire leads to the same transformer terminals on the same circuit by noting the ridge or marking on one side of the cable.

Straight: The straight wiring method is a “straight” run of fixtures connected directly to the transformer tap in a “daisy chain”. The furthest fixture from the transformer will experience the largest voltage drop and therefore will be the dimmest; likewise, the fixture closest to the transformer will be the brightest. Use this method when it is not practical to loop it back to the transformer. If any of the fixtures are rated at less than 10.8V, please see the section above on methods to boost the voltage.

Hub Junction: The Junction wiring method represents a group of fixtures that are each connected to a hub, which is then connected to the transformer. This hub would need to be buried in a location central to all fixtures; however fixtures do not need to be equal distance from this hub, so long as the wire length is uniform. Any extra wire should be buried near the fixture, and never cut. This allows for complete distribution of power to each fixture ensuring even brightness in all fixtures. This type of install is ideal for circular drive ways or paths where voltage drop among fixtures might be noticeable.

Tree Wiring Methods

Tree mounting method main run up the tree

Flexible 1/2" copper tubing and pipe straps on the lower part of the tree, typically up to the first or second branch structure, this will protect the wiring and ensure safety for kids or dogs. The copper will patina and match the bark of the tree in a short period of time.

Arrow T59 Staple gun and the appropriate Stainless Steel T59 Staples. On mature trees the staples grow out with the bark. On smaller immature trees you will have to inspect and adjust the cabling as part of your yearly re-lamping.

Black cable ties (Tywraps/Zap straps) that have a small eye hole up near the buckle so you can zip it around a wire then use an appropriately sized stainless steel screw through the eye ring to fix the wire to the tree. Remember don't screw it all the way down, leave it backed out a bit, and back it out some more, as needed, during service visits. Otherwise, the tree may grow around the fitting.

Don’t forget to leave a drip loop at the bottom of the tree.

Tree mounting method for fixture mounting

3 point mount uses 3 lag bolt or stainless screws. Typically used for HID or heavier fixtures where a 120 volt junction box is required. This method requires yearly inspection and possible relocations.

2 point mount uses 2 stainless screws. Typically used for low voltage fixtures, requires yearly inspection, but seldom requires relocation.

1 point mount uses a stainless screw and ensures the tree growth will not splay at the fixed point.

Don’t forget a tree grows thicker while the top grows up, the screw/bolt/fixture won't require more wire.

Voltage Drop

Voltage drop on your system will affect lamp life and the amount of light the lamps will deliver.  Too much voltage drop lowers the light output and changes the color of the light from white to yellow or orange.  Too little voltage drop burns the lamps too hot and shortens lamp life. 

The following table shows the effect of voltage drop for standard non-halogen lamps:

As you can see, a lamp with a design voltage of 12 volts will deliver 80% of its light output and it's life will double by reducing the voltage 0.5 volts.  The light loss is hardly noticeable to the naked eye while the lamp life is greatly extended.  Therefore, in the outdoor environment, we want to experience a slight voltage drop to all lamps.  The recommended feed to each lamp is 10.8 - 11.5 volts.

Keep in mind that with halogen lamps, such as the MR16, a voltage feed of less than 10.8 volts may adversely affect lamp life.

How to determine voltage drop

Total Watts X Length of Run ...Divided by Cable constant =   Voltage Loss

• Total Watts - Add up the number of lamps and the wattage of each lamp on each run.
• Cable Length - Length of cable used (in feet) from the transformer to the fixture for which you are calculating voltage drop.
• Cable Constant - Indicates thickness of copper wire.  The thicker the wire, the lower the conduction resistance and the lower the voltage drop.

How is the voltage determined at each lamp?

Voltage at each lamp is determined by subtracting the voltage drop at each lamp from the voltage at the transformer.  The voltage at the transformer will depend on:

1. Which voltage tap is being used (11 volt, 12 volt or 13 volt).
2. The total load on the transformer.
3. the voltage feed to the transformer.

Try to locate the transformer in the most central location possible.  Voltage drop can be controlled by:

1. Using the proper voltage tap on the transformer.
2. Center feeding to the load of each run.
3. Using proper cable size.
4. Using fewer fixtures on a cable run.
5. Using lower wattage lamps.

Conclusion

Any of these methods can be used in conjunction with each other. Since there are so many variables involved, it is suggested to use the voltage drop calculation to get you in the ball park. It is always recommended to check the actual voltage readings at each fixture with a volt meter before burying the cable. This allows for much easier wiring connections.

In short, the simplest and easiest way to lay out your wire runs is to connect all wires and fixtures, leaving the cable above ground. Then take a voltage meter reading at the first fixture. It should read 11 volts to 11.5 volts. If you have followed all of the recommendations above and on the other pages, all other fixtures should be receiving a minimum of 10.8 volts, but check them to make sure.

How The Pro's Do it

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