Voltage drop calculation

Stan in Oly, WA

Well-known Member
Online voltage drop calculators are easy enough to use, but what if the problem isn't so uncomplicated? I have a 200 amp electrical service. There is a 120 volt outlet in my garage that is 60 feet of 12/2G solid house wire away from the breaker panel. It is on a 20 amp breaker. I need to run a power tool that draws 15 amps at a location 70 feet from the outlet in the garage. I have three 25' extension cords, one 10 gauge, one 12 gauge, and one 16 gauge. Does the order in which I connect the extension cords make any difference in the amount of voltage drop I will experience at the location where I want to use the tool?

Stan
 
No, series resistance is simply additive and all will be in the circuit no matter how you connect them.
 
I agree with Bob, in that V = I x R regardless where you place it in a series circuit, but however you connect all them cords, my guess without running the calculations are if a tool draws 15 amps and you're working out at the end of all those connections and plugs and receptacles and extensions cords (each with some degree of resistance and voltage drop) you may be crowding things a bit, probably still "work"... When I designed even before I ran voltage drop I sized my conductors to have an ampacity of at least 125% over the maximum continuous current which would be 16 amps on 12 gauge wire so you can see my concern. Again, it can "work" with what you have (depends on the tool and its design and how low voltage affects it, could run on the warm side??), Ive seen Billy Bob and Bubba do far worse an by golly they say it worked fine........

John T
 
You won't get so much of a voltage drop until you get to the extension cords, especially the 16ga one. Unless it's an air compressor it should work unless used constantly. If it's something you would use often it would be better if you buried some underground feeder wire and set up an outlet at the source. Still if you are trying to run an air compressor it would be better to plug the compressor in at the garage and get more air hose.
 
Answer is no it doesn't make a difference the order of extension cords.

Most tools have a universal motor, motor with brushes. Universal motors can run of a few less volts and you won't be able to tell the difference in a little voltage loss.
 
I have thought about the same scenario some time ago and used my meter to test it, did not find any difference. Put a voltmeter at the end of the line and test it when you start the tool.
 
I give all my 16 gauge extension cords to someone I don't really like. They are pretty much useless. I had a weedwacker that would be so intermittent when I used the 16 ga cord. Buy a good 50' 12ga or two. You will never look back.

I have some hose hangers on the wall and "wind the cord like a roadie" That way it doesn't twist when you take it off the hanger.

Cords like wires have amperage ratings.
12 ga-20A
14 ga-15A
16 ga-give to someone you don't like
 
(quoted from post at 06:43:15 09/05/16) I give all my 16 gauge extension cords to someone I don't really like. They are pretty much useless. I had a weedwacker that would be so intermittent when I used the 16 ga cord. Buy a good 50' 12ga or two. You will never look back.

I have some hose hangers on the wall and "[b:5d3a7073f7][i:5d3a7073f7]wind the cord like a roadie[/i:5d3a7073f7][/b:5d3a7073f7]" That way it doesn't twist when you take it off the hanger.

Cords like wires have amperage ratings.
12 ga-20A
14 ga-15A
16 ga-give to someone you don't like

Do you get as irritated as I do when someone wraps cords as tight as possible?

I also went to 12 gauge extension cords except for a couple of dedicated uses where 14 gauge is more than adequate
 
I think voltage drop must be very negligible ....for fun a couple of years ago my Dad and I rolled out 600' of extension cords from his house to my cabin on the property next door. These were a mix of 12, 14 and mostly 16 gauge cords. I put my volt meter at the end of 600' and the voltage was no different than at the house. I used the power for light and a battery charger. Of course I wasn't going to use any power tools but I'm curious like Stan what the real formula is??
 
Were you drawing much current when you measured the voltage? With almost zero current flowing there would be zero voltage drop. Ohm's Law is V=I x R. It would have been interesting to measure the resistance of those 600 feet of extension cords connected in series.
 
Thanks for your insight...and no there was no load or draw when checking voltage at the 600' point. Lightbulbs were just as bright as at the other end. I wish in hindsight I would have done more investigation at the time.
 
Still, I would connect the cords in order of heaviest to lightest starting at the outlet.

The 16ga cord is the lightest, so it would be the easiest one to carry the farthest.
 

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