Same Run, Multiple AWGs & Voltage Drop?


Old 08-13-05, 06:53 PM
Thread Starter
Join Date: Apr 2005
Posts: 37
Same Run, Multiple AWGs & Voltage Drop?

I have a refrigerator/freezer in my detached garage that is used for frozen foods and any overflow that will not fit into the refrigerator/freezer in the kitchen. During the last power outage, of over 3 days, all of the food spoiled.

I recently purchased a 7500-watt portable generator with a surged wattage of 13500 and a 30-amp transfer swatch. It is working perfectly to power the basement sump pump and refrigerator/freezer in the kitchen.

I would like to also supply the refrigerator/freezer that is in my garage. I would like alternate powering the 2 refrigerator/freezers on and off in approximately 1 hour intervals in the event of any future power outages.

The generator cord is #10 with 4 conductors and 15 feet in length and plugs into the power inlet box and feeds the transfer switch. The feed to the detached garage from the main panel is #6 THHN (4 wires) and is approximately 100 feet long to the sub panel in the garage. The branch circuit that feeds the refrigerator/freezer is #12 and approximately 35 feet long to the receptacle.

My question:

The appliance draws 11.6 amps at 115 volts. How do you calculate the voltage drop for 15 feet of #10, 100 feet of # 6 and 35 feet of #12 all in the same run?

I hope that my explanation and question is clear.

Thanks in advance for any advice or guidance.

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Old 08-13-05, 07:34 PM
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
To calculate voltage drop, you use a calculator. Google the term "voltage drop calculator" and you will find many of them.

However, I would not be too concerned with the results. If things are working now, they would work okay when using the generator.

Of bigger concern would be how the main panel is fed. What type of transfer switch is this? Is it one that only has a few breakers? If so, then it won't power your main panel (and hence the garage). If it does feed your main panel then you are okay.
Old 08-13-05, 08:24 PM
Thread Starter
Join Date: Apr 2005
Posts: 37
Hi racraft,

Thank you for your response. However, I must apologize for my original post. After reading it myself, I realized that I had too much garbled information and did not get to the point.

Let me rephrase the question:

I want to power an appliance that draws 11.6 amps at 115 volts ac. The wiring run is 150 feet long. The run is composed of 15 feet of #10 AWG, 100 feet of #6 AWG and 35 feet of #12 AWG. Can someone here calculate the voltage drop? or advise how I can?

Again, I want to apologize for my original, poorly explained post.

Old 08-13-05, 09:53 PM
Join Date: Sep 2000
Location: United States
Posts: 18,497
Use any of the voltage drop calculators to make three separate calculations.
  1. 11.6 amps for 15 feet of #10.
  2. 11.6 amps for 100 feet of #6.
  3. 11.6 amps for 35 feet of #12.
Then add the voltage drops together (the volts, not the percentages). That will give you the total drop.
Old 08-14-05, 12:52 AM
Join Date: Oct 2004
Location: USA
Posts: 719
Originally Posted by John Nelson
  1. 11.6 amps for 15 feet of #10.
  2. 11.6 amps for 100 feet of #6.
  3. 11.6 amps for 35 feet of #12.
Then add the voltage drops together

(1) 0.4 volts
(2) 1.1 volts
(3) 1.6 volts
Old 08-14-05, 09:26 AM
Join Date: Nov 2004
Location: CA
Posts: 2,041
I wonder if a second generator wouln't be less expensive than the timed switcher you are looking for.

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