mobiledynamics
Well-known member
A 10 Gauge extension cord at 100ft......would that be a 20 amp rated cord or 15 , after taking into account voltage dropoff ?
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Voltage Dropoff
- Thread starter mobiledynamics
- Start date
OP
mobiledynamics
Well-known member
I just realized I had a 10/3 100 lying around.
Did a non scientific test with my Fluke 189
123.7'ish right off the outlet on my wall.
Plugged in the cord and off the other end, getting similar 123.7'ish....
Did a non scientific test with my Fluke 189
123.7'ish right off the outlet on my wall.
Plugged in the cord and off the other end, getting similar 123.7'ish....
hh76
Well-known member
A 10 Gauge extension cord at 100ft......would that be a 20 amp rated cord or 15 , after taking into account voltage dropoff ?
I'd guess that it is rated at what is written on the package, that they would have figured in the length for the consumer.
At 20a, the voltage drop should be 4%, or down 4.8v
At 15a, 3%, or 3.6v
I just realized I had a 10/3 100 lying around.
Did a non scientific test with my Fluke 189
123.7'ish right off the outlet on my wall.
Plugged in the cord and off the other end, getting similar 123.7'ish....
No current, no voltage drop.
But if you're not pulling any current thru the extension cord, you're not going to get any voltage drop.
Put some sort of load on the end of the extension cord, measure how much current it's drawing, and then measure the voltage at the 'far' end of the extension cord.
Put some sort of load on the end of the extension cord, measure how much current it's drawing, and then measure the voltage at the 'far' end of the extension cord.
offroadsteve
Well-known member
Voltage drop over a length of cable is a function of voltage and current flowing. Think of the wiring like a pipe. Voltage is similar to pressure and flow rate is similar to current. If you try to draw (****) too much flow out of an undersized pipe, pressure is going to drop. If you ignore power factor and other electricity related phenomenon, the same thing happens in electrical wires.
You are not going to see any voltage drop in a no-load condition. This would be like measuring the pressure in a pipe with no flow. Your Fluke is essentially infinite resistance, so the current draw is very nearly zero. You could lay out 1000' of 22 gauge Cat 5 cable and not see any voltage drop with a DMM.
But.. that doesn't answer your question. Using Southwire's voltage drop calculator:
http://www.southwire.com/support/voltage-drop-calculator.htm
To keep voltage drop below 3%, which is recommended, you are limited to 15 amps at 120V or 30 amps at 240V.
You are not going to see any voltage drop in a no-load condition. This would be like measuring the pressure in a pipe with no flow. Your Fluke is essentially infinite resistance, so the current draw is very nearly zero. You could lay out 1000' of 22 gauge Cat 5 cable and not see any voltage drop with a DMM.
But.. that doesn't answer your question. Using Southwire's voltage drop calculator:
http://www.southwire.com/support/voltage-drop-calculator.htm
To keep voltage drop below 3%, which is recommended, you are limited to 15 amps at 120V or 30 amps at 240V.
wyliesdiesels
Well-known member
Voltage drop over a length of cable is a function of voltage and current flowing. Think of the wiring like a pipe. Voltage is similar to pressure and flow rate is similar to current. If you try to draw (****) too much flow out of an undersized pipe, pressure is going to drop. If you ignore power factor and other electricity related phenomenon, the same thing happens in electrical wires.
You are not going to see any voltage drop in a no-load condition. This would be like measuring the pressure in a pipe with no flow. Your Fluke is essentially infinite resistance, so the current draw is very nearly zero. You could lay out 1000' of 22 gauge Cat 5 cable and not see any voltage drop with a DMM.
But.. that doesn't answer your question. Using Southwire's voltage drop calculator:
http://www.southwire.com/support/voltage-drop-calculator.htm
To keep voltage drop below 3%, which is recommended, you are limited to 15 amps at 120V or 30 amps at 240V.
The NEC recommends 3% for feeders and 5% for branch circuits! So, running a 20a load through the cord would give him an approx 4% drop(4.96v) which is acceptable!
OP
mobiledynamics
Well-known member
Let me tell you where I'm going with this this......
Due to other things taking precedence this spring/summer (home renovations + another renovation at my pops), I won't be doing the inlet/transfer switch setup. It's not a easy route for the inlet job - as the route it needs to take will require some new rock/mud/paint and moving of some stuff as well
The minimum run is 75 feet of wire from the generator - That distance is how far out I plan to have the generator to the cord I plan to use to get it inside a window in the house. The distance is due to the fact that I want to minimize the chance of a backdraft of CO coming into the house. I read too many stories during/post Sandy about how people died unknowilling due to CO backdraft coming into a window.
I was planning to use 10/4 but maybe 8/4 might be the wiser of the 2. And more costly of the 2.
As far as usage, the primary usage if the generator is needed is a sump pump, and 1 or 2 utility surface pumps going at the same time
Then, once the SHTF is over, I can deal with the alternating the 2 fridges, etc.
I think I should okay with the 10awg based on the concurrent loads I'll be giving it....
Due to other things taking precedence this spring/summer (home renovations + another renovation at my pops), I won't be doing the inlet/transfer switch setup. It's not a easy route for the inlet job - as the route it needs to take will require some new rock/mud/paint and moving of some stuff as well
The minimum run is 75 feet of wire from the generator - That distance is how far out I plan to have the generator to the cord I plan to use to get it inside a window in the house. The distance is due to the fact that I want to minimize the chance of a backdraft of CO coming into the house. I read too many stories during/post Sandy about how people died unknowilling due to CO backdraft coming into a window.
I was planning to use 10/4 but maybe 8/4 might be the wiser of the 2. And more costly of the 2.
As far as usage, the primary usage if the generator is needed is a sump pump, and 1 or 2 utility surface pumps going at the same time
Then, once the SHTF is over, I can deal with the alternating the 2 fridges, etc.
I think I should okay with the 10awg based on the concurrent loads I'll be giving it....
Last edited:
hh76
Well-known member
Let me tell you where I'm going with this this......
Due to other things taking precedence this spring/summer (home renovations + another renovation at my pops), I won't be doing the inlet/transfer switch setup. It's not a easy route for the inlet job - as the route it needs to take will require some new rock/mud/paint and moving of some stuff as well
The minimum run is 75 feet of wire from the generator - That distance is how far out I plan to have the generator to the cord I plan to use to get it inside a window in the house. The distance is due to the fact that I want to minimize the chance of a backdraft of CO coming into the house. I read too many stories during/post Sandy about how people died unknowilling due to CO backdraft coming into a window.
I was planning to use 10/4 but maybe 8/4 might be the wiser of the 2. And more costly of the 2.
As far as usage, the primary usage if the generator is needed is a sump pump, and 1 or 2 utility surface pumps going at the same time
Then, once the SHTF is over, I can deal with the alternating the 2 fridges, etc.
I think I should okay with the 10awg based on the concurrent loads I'll be giving it....
You'll be fine with the 10awg. Chance are you won't be drawing the full 20a too often, and even if you are, 4% is not out of the line for drop.
Keep in mind that your generator, even the grid in some locations, will probably have greater flucuations in voltage than your cord will be causing.
OP
mobiledynamics
Well-known member
I have to google and read...cause I thought certain motor based things did not like too much variation in voltage...causing them to go bad. Applicances or fridges if I recall
hh76
Well-known member
I have to google and read...cause I thought certain motor based things did not like too much variation in voltage...causing them to go bad. Applicances or fridges if I recall
True, motors can have a significantly reduced lifespan, that is why we try to keep the drop to less than 5% overall.