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Engineering Mechanics of Your Landscape Lighting System

[ Posted On: 2007-01-31 ]

This article will be a breath of fresh air for some of you and a gut wrenching process for others. Without getting too involved within the process, I will say this particular piece of the puzzle is designed for the person that thinks with the left side of your brain.

Their many studies and books written about the left side and right side of our brains. Many people enjoy a "good" living dealing with issues relating to the left and right side of our brains. This could be the start of another book relating to that subject; however, I am not going there. Too keep this to the simplest form I can, I will say our brain is divided into two sides. We have the left side and the right side.

The left side of the brain functions by way of using logic, facts, knowledge, math and science and is detailed oriented. If you fall into this category, you will enjoy this article.

Meanwhile, the right side of the brain functions by using feelings, images, symbols, sees the "big picture", is very imaginative and believes things are possible by taking risks. If you fall into this category, I hope your partner is a left-brain person. This article will be dull and boring for you even though it is an extremely important process for you to achieve your "big picture" on your home to create the "WOW" effect you want.

My wife and I are a good team because she is a professional photographer, thus a right brain person. I am a left-brain person. We compliment each other and guess who takes pictures of my landscape-lighting installations.

A good starting subject for this article is "voltage drop". Voltage drop is created by internal resistance to the flow of electricity through electric wire or cable. It is the difference between the voltages at the beginning of a cable run compared to the voltage at the end of a run. We need to compensate for the voltage drop in order to keep the same voltage to all fixtures. If we do not, the end fixtures will have lamps with low voltage and the results will be a decrease in brightness. This is why we can see the yellow looking lights at the end of the runs.

The formula for calculating voltage drop is:
Total Watts x Length of Run / Cable Size Constant = VOLTAGE DROP

You are now asking yourself, "What is cable size constant". That is a predetermined amount and I will not show the chart for the different size cables. Instead, I will share the constants that you will use for your system. Use either a 10/2-gauge wire, which has a constant of 11920, or a 12/2-gauge wire, which has a constant of 7500.

With this information and the constants, lets figure a "run for fun". This example shows a run for 80 feet and on the run, there are 4 fixtures that have a 20-watt lamp in each. We have a total of 80 watts on a run of 80 feet and 12/2 gauge wire is used for the run.

80-watts x 80 feet =6400, 6400/7500 (constant) = .85 voltage drop

Now subtract .85 (voltage drop) from 12 (amount of volts from source) and we have a resulting voltage reading of 11.15 volts. I like to keep lamps in a range of 10.5 volts to 11.7 volts for peak performance; therefore, the reading of 11.15 volts fits very will within the range. The main thing to remember is to choose the lamp you want and need to do the job you want. Once you decide on the lamp, engineer the system to supply the proper voltage to the lamp.

A rule of thumb on sizing wire for runs is to always go bigger if there is some doubt. The 10/2 gauge wire expense is just slightly higher than the 12/2 gauge wire; however, the peace of mind is well worth the difference. I have included a flowchart to use as an estimate on which gauge wire to use on which run. This does not replace the voltage drop formula and measuring every lead to every fixture using a multimeter to get the proper reading. For runs over 100 feet I recommend using the 12/2 gauge cable just because it can handle more with less voltage drop.

QUICK WIRE SIZING GUIDE: Use the guide to select wire sizes for each run:

"Are there more than 100 watts lamp load on the run"?

If your answer is, yes then you Use #10-2

If your answer is no then the next question is "Is the run longer than 100 feet? If your answer is no you Use #12-2 and if its Yes then you Use #10-2

WIRE AMP RATINGS:

Wire Size #12/2 100w/8.3A is recommended and the maximum is 192w/16A

Wire Size #10/2 140w/12.0A is recommended and the maximum is 288w/24A

You will notice the flowchart gives the wire size with recommended and maximum figures. It gives reference to watts and amps. Remember the formula: (Amps x volts = watts Or Watts/volts = amps)

You will be fine on amps using these guidelines. I keep a maximum of 110 watts per run on 12/2 cable and 150 watts on 10/2 cable. I know the system is not working hard and I feel that it will produce an efficient operating system.

Article Source: http://www.afroarticles.com/article-dashboard

About The Author: Roger Neumann graduated from Southern Illinois University with a B.S. degree in Business Administration. Roger has created a system that anyone can follow and be successful installing landscape lighting for their home. For more info: www.abclandscapelighting.com. He incorporated the flying protocol of using a checklist and planning to create his system. His “how to” book on installing landscape-lighting systems: www.landscapelightingabc.com

| View Profile & All Articles By: Roger Neumann |

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