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View Full Version : Voltage Drop???


ok4me2xlr8
07-25-2007, 09:53 PM
I am kinda new at this and would like to know is there a tool that i can use to figure voltage drop on a long string of lights???

Chris J
07-25-2007, 11:31 PM
First of all, you never want to have a "long string of lights." Your lights should never be more than about 25' away from the point at which the power splits off. In other words, group your fixtures together and use multiple runs of wire. You can use a hub method, T method, loop or lollipop but don't ever daisy-chain fixtures unless it's only a couple of fixtures that are within a few feet of one another.
To calculate voltage drop, there are several different ways to do this. Some are very complicated, and some manufacturers provide software that will do this for you when you enter the required data (ie, length of run, total wattage and guage of wire). A very common way to calculate voltage drop manually is to multiply the total wattage on the run by the length of the run. You then divide this number by the cable constant (7500 for 12-2 and 11920 for 10-2). When you arrive at that number, I usually multiply it by 1.5 to get a very good result.
Example: 3 fixtures (35w each) at the end of 100' of 12-2 cable would look like this: 105w X 100'= 10,500 ..........10,500/7500= 1.4...........1.4 X 1.5 = 2.1 volts of drop. You would want to put your cable in the 14v tap in order to have 11.9v at the first fixture or put it in the 13v tap to have 10.9v at the first fixture.
This is a simple way to do "desk estimates" but your final assesment should ALWAYS be done with a voltage meter. Most manufacturers offer seminars and training courses. You can also become a member of the AOLP or other similar organization to better educate yourself on the proper techniques required to install lighting systems. If you start out on the wrong foot now, these installations that you are doing will come back to haunt you down the road. Trust me, these people will not lose your phone number and they will expect you to fix their lighting systems. Don't do harm to your business right out of the gate. Learn the basics of the biz before you get too far into it.

sprinkler guy
07-26-2007, 03:08 AM
Chris,

Something I've found real helpful recently is the tin-coated wire from Cast. Footage markings on it every 12" inches, which takes the guess work out of wire run lengths. This saves me from measuring off later as I calculate for the right tap. Its also helped me a couple times when the gardener was planting a new tree or shrub in an area where I had more than one wire in the trench. I showed up to fix the breaks and I matched up the footage markings for a quick repair.

ok4me2xlr8
07-26-2007, 09:12 AM
thank you all for the information if any one has the software or a website with the software will you please send it to me at ok4me2xlr8@carolina.rr.com

Chris J
07-26-2007, 06:29 PM
I frequently buy wire that also has the footage markings on it, but I don't use tin coat. The markings do come in handy at times. Believe it or not, however, I rarely measure anything. I usually just guesstimate the approximate distance when I am calculating my wiring designs. I do all of this "desk estimating" before I even get to the job, and it is usually pretty accurate, however I always ensure proper voltage by testing with my volt meter. This is the only way to accurately ensure you have it right on the money.

Chris J
07-26-2007, 06:31 PM
thank you all for the information if any one has the software or a website with the software will you please send it to me at ok4me2xlr8@carolina.rr.com

Kichler has the software, so does Cast, Unique and many others. I don't know if they will give it to you freely, or if you will have to sign up with their respective programs. It doesn't hurt to ask.

carcrz
07-26-2007, 07:08 PM
Kichler has a 30 day demo that has the option to buy for $100I used it to play on my house a little.