Efrain Ramirez, Lighting BDR for Horizon, shows how to choose the right voltage tap on your transformer by calculating the total voltage drop throughout the lighting system.

Video Transcript

Hello, my name is Efrain Ramirez, Lighting BDR for Horizon, and your next period of instruction is going to be on voltage drop.

As you can see here, we’re going to be calculating voltage drop on an LED Hub Method. Now to do that on the bottom left hand corner circled in red is the formula for your voltage drop calculations.

VD = ((L x W)/WC) X 2

Now let me go over that. The “L” represents length of the wire times your wattage. Dividing by your wire constant. Times 2.

Now your wire constant, as you can see on your chart on the right hand side, when using 12 gauge, your wire constant will be 7500. 14 gauge is 3500. Now these are the two gauges that we’re going to use in this example here.

So as you see, that on your home run, your 12/2 is 150 foot times 75 Watts, which is your total load on this one home run. That equals 11,250. You take that number and divide it by your wire constant, which is 7500, it gives you 1.5. Multiply that times 2 and you get a voltage drop of 3.

Once you’re done doing your voltage drop on your whole entire system, you calculate individual legs.

As you’ll see here circled in red, you have 50 foot of 14/2 times 25 Watts equals 1250. Divide that by your wire constant, which is 3500. It gives you .3571. Times 2 is .71 voltage drop.

The same thing here. We’re using the same gauge wire. Same distance. So if you have 50’ x 25w = 1250. Divide that by the wire constant 3500. Gives you .3571. Times 2 is .71 voltage drop on that leg.

Now your top leg circled in purple, same exact calculations. You have 50 foot times 25 watts of load equals 1250. You divide that by your wire constant, 3500, comes out to .3571. Times 2. It’s .71 voltage drop there.

Once you calculate everything, you add all your calculations up, which gives you 5.13 of total voltage drop. Now once you’ve done that, you simply add that to 12 volts, which that you want at your fixtures. So you’re going to be utilizing 12 volts.

See at the very bottom left, we have added all of your voltage drop calculations. It gives you 5.13 Voltage Drop. And on your far right, you’ll be utilizing your 17 Volt Tap on your transformer.

That concludes my period of instruction on Voltage Drop.