Landscape Lighting: Voltage Drop and Wiring Methods
Every lighting job and every lighting system are the same, right? Well, not quite. The wiring method used can affect both system performance and, more importantly, the visual outcome (the lighting portrait). We will compare the most common wiring methods below, but before we do that, let’s consider the nemesis of wiring any landscape lighting system: voltage drop.
To control voltage drop in low-voltage landscape lighting systems, there are two things to consider. The first is having a multi-tap transformer to compensate for voltage drop by having several higher-voltage taps available. When utilizing a higher-voltage tap at the transformer, the voltage starts out high then drops down to the proper voltage as the power travels through the wire to the fixtures. There is really only one way to confirm that you are getting proper voltage to your light fixtures — by verifying and testing with a digital voltmeter.
Second, you need to be able to distribute equal voltage to every single fixture in your landscape lighting system, and that takes a well-planned wiring method. The only wiring method that can get equal voltage to every fixture is an equalized hub method of wiring. This method requires equal lengths of wire on all fixtures leading to a central connection point (a hub).
There are many myths, misconceptions and falsities out there in the common understanding of voltage drop. Even many lighting manufactures now say that you can “live” with voltage drop. With the advent of LED lamps with a range of 10 to 15 or 18 and even up to 30 volts, you would think “Oh boy, isn’t this great? No more voltage drop.” Well, this is really doing an injustice to our industry.
To explain, take the following example: A truck engine is designed to run optimally at 2,200 rpm, but I run my engine at 2,200 rpm, and you run yours at 4,000 rpm. Both engines will work, but my engine (running at 2,200 RPM) may last 200,000 miles or more. The engine running at 4,000 RPM may fail considerably sooner. Similarly, LED lamps have an hour rating of 20,000 to 40,000 hours, but not all LED lamps run at their peak performance. Years of lamp testing reveal that changes in voltage (decreasing and increasing the voltage) affect the internal electronics and drivers in four ways:
Lamps are most affected by heat (the killer of LED lamps).
Volt amp changes in the lamps. For example, a 4-watt lamp might pull 6 watts (that’s a 50% increase).
Color temperature shifting.
Now, that being said, all LED lamps have some increase due to the electronic driver. Make sure you use a true RMS amp meter; this will ensure that you do not overload the wire, transformer or fuse.
So the goal then is to get 12 volts to all LED lamps. Let’s do everything we can to help them live a long happy life. Use a multi-tap transformer — they have been available for more than 20 years; and although we are using smaller-wattage transformers today (100 to 300 watts) we should still use a 12, 13, 14, and 15 multi-tap transformer.
Besides the potential shortening of lamp life, we should also think about the future and the potential “what-ifs.” For example, what if your system is on the edge of 10 volts and you want to add lights? Or, what if your voltage changes from daytime to nighttime? This is a typical situation and happens all the time because we usually check voltage in the daytime when it is typically higher by 5 to 10 volts than at night. Daytime line voltage at 130 volts ‘in’ giving 13 volts out of the transformer and 10 volts at the lamps can change at night to 120 volts ‘in’ giving 12 volts out of the transformer and 9 volts at the lamps. The other big voltage drop killer is that we typically tap into an existing outlet, and the homeowner adds something to that circuit, thus causing voltage drop. How do you solve this issue? If you have a multi-tap transformer, all you have to do is change to a higher tap at the transformer, and the voltage will increase to the lamp.
Now let’s move on to wiring methods. One of the most common methods of wiring has been the “daisy chain.” The daisy chain brings power to the first lamp (fixture) on a wire run, often called the “home run.” That first fixture receives the most voltage or power. The remaining fixtures get less and less voltage in sequence. The number of fixtures and the wattage of lamps along with the wire distance will determine the voltage disparity. Sometimes in lighting designs, you are very limited on your wiring space. The one and only time a daisy chain method can be useful is when you mount fixtures above ground and out of the earth. As soon as you put the system into the ground, you are asking for trouble with bad or poorly made wire connections.
There is really only one advantage to the daisy chain method, and that is when placing fixtures in hard-to-reach areas such as rain gutters, second stories and under fascia. There are many more disadvantages, including too many points of connection, time consuming install, difficult to troubleshoot, short wire leads do not allow for much movement at the fixture, and daisy chaining does not get equal voltage to all lamps.
One last point of concern with the daisy chain method is that generally every fixture needs splicing into place, creating the multiple points of connection expressed above. This greatly increases the potential of having a failed connection due to water infiltration, or a bad mechanical connection resulting in a heat buildup and melting of the wire. Due to the large amount of potential voltage drop, you might also experience failing lamps and a poor-looking lighting job due to unequal voltage.
Another common method of wiring is known as the “loop” method. The loop method brings the same voltage and power to both ends of the wire run. When using this method, the home run wire goes to the first fixture, other fixtures are then daisy chained while maintaining wire polarity (very important). After installing the last lamp, the second wire is “looped-back” to the first lamp and tied in. A similar method is used in irrigation by double feeding the sprinkler zone to help equalize the water pressure throughout. It works the same way in electrical wiring by providing the proper voltage to both the first and last fixture on the wire run, helping stabilize the electricity to all fixtures — but only to a point.
When using the loop method, the one thing you must be entirely sure about is matching the polarity of the wires or you will create a short, possibly causing bodily harm or damage to the circuit. Matching wire polarity is easy to do; just connect the wires with identical markings to each other. One last caution: do not cut into the “loop” part of the wire when you add a fixture, because you will minimize the loop’s stabilizing effect on the voltage.
The main advantage of the loop method is that it can be a quick way to remedy an existing daisy chain voltage drop problem. Unfortunately, the loop method shares many of the disadvantages of daisy chaining, such as multiple points of connection, time-consuming installation, difficulty troubleshooting, short wire leads that do not allow for much movement at the fixture, and the loop method does not get equal voltage to all lamps. There is one more disadvantage: the loop method wastes a lot of wire completing the loop (double the wire).
Next is the “T” method. Although not as common as some other methods, the “T” method brings your home run wire to the middle fixture first, then “T’s” off in both directions. This cuts the wire lamp load in half, in essence, cutting the voltage drop in half too. This method is great for placing fixtures in hard-to-reach areas. (Note: you can use the loop and “T” methods together.)
Again, many of the same disadvantages mentioned above hinder the “T” method and you can add one more — this method requires the use of heavier-gauge wire. With the “T” method, you are still not getting equal voltage to all lamps, and you can still have numerous connections in the ground. What you are seeing with all of the above methods is that you have all of the same issues, but to different severities.
The HUB method
Wiring a lighting job and achieving no connections in the ground can only be done using the HUB method. The HUB method is simple: you run a home run wire from the transformer to a HUB and then connect all your fixtures to the HUB — that’s it!
The HUB method solves the two biggest problems you face:
Reducing in-ground connections, corrosion and wicking. Wicking draws moisture up under the insulation where it hides, doing its damage by tarnishing the copper wire and destroying conductivity. Check any wire nut connection unprotected in the ground, and you will see for yourself.
Not being able to relocate a fixture due to changes in the landscape (landscape growth, changing landscape features).
The HUB method is the best way to wire, because it delivers proper voltage to each lamp. It is easier to avoid any wiring mistakes in the field too. There is no wrong polarity, no imbalance, no looping, no wicking and no corrosion. Always buy fixtures with a 25-foot wire lead, and then simply connect them to a HUB that is a central point of connection.
Advantages of the HUB method are many:
Equal voltage to every lamp.
One point of connection per home run.
No connections in the ground.
Saves cost on wire by using less.
You can use a smaller-gauge wire.
Great savings on labor.
The ability to install a secondary fuse for protection.
Allows you to easily add more fixtures later.
You can cut your wire connections by 80% with the HUB method.
You are able to check voltage at the HUB instead of finding each fixture.
Easy to troubleshoot since each fixture is wired to the HUB (you can either use an amp probe to determine shorts and lamp wattage or disconnect individual fixtures for line testing).
Use the HUB wiring method on every job for a dependable wiring system. Contractors and their customers benefit from the reliability, flexibility and ease of future expansion.
Content for this article by Nate Mullen (a.k.a., The Illuminator) and Unique Lighting Systems. Visit the Unique Lighting Systems website at www.uniquelighting.com for more information, great “how-to” videos, and to see all the Unique Lighting fixtures, HUBS, transformers and LED lamps.