What guage do extension cords need to be?

[freefly23]

If anyone is familiar with why we need thicker guage wire for longer distances, could you please explain it to me? So take a chart like this:




If we need 15 amps, but are using 3, 50 feet extensions cords for a total of 150 feet, would we need 6 guage extension cords or would 12 guage meet the requirement?

Thanks for the help!

[ryanjones2150]

What guage do extension cords need to be?

What are you trying to run power to and for how long?

[fabricator]

3 x 50' =150'
150 feet at 15 amps require 6 guage.

[fabricator]

Electrical resistance is the reason a larger guage is needed at greater distances to carry voltage.

[WillieB]

If you learn the math of a series circuit, you find that each component carrying current offers some resistance. each component will have full and equivalent current or amperage. Voltage will be divided among the resistors. The greatest resistance consumes the most voltage. Larger conductors offer less resistance. In incandescent or resistive loads, losing voltage isn't as punitive. A bulb isn't as bright, a heater produces less heat. Motors behave differently. At rated, or slightly above rated voltage they work well. At less than rated voltage less magnetic field is produced. It's the magnetic field that offers a choke effect, therefore current increases in a resistive sense, while magnetic field is weakened. The motor gets hotter as in more BTUs, and turns slower, with a weaker blower for cooling.

A bigger wire gauge cord provides more voltage to the power tool enabling it to work as it was designed.

[ryanjones2150]

Wireless electricity. That would be Tesla's solution.

[MMW]

I don't understand what this thread is about? The chart at the top of the page is either not related to the question (if there is one) or taken out of context from somewhere. You would not drag around a 6 gauge, 150' extension cord to run a 15 amp grinder.

[Meltedmetal]

I think it depends what you are doing with the 15 amps at the end of 150 feet of cord. As Willie explained if you can live(or your tools can live) with the voltage drop over that distance then you are good with a smaller cord but if you need a full 15 amps at 100% duty cycle you would have to go with a larger conductor to maintain the voltage at that draw.

[OscarJr]

I think it depends what you are doing with the 15 amps at the end of 150 feet of cord. As Willie explained if you can live(or your tools can live) with the voltage drop over that distance then you are good with a smaller cord but if you need a full 15 amps at 100% duty cycle you would have to go with a larger conductor to maintain the voltage at that draw.

Exactly. The more voltage drop, the more current the tool can attempt to draw from the circuit, which won't always happen due to resistance as well. Will tools work with sub-par wiring sure? But the total power delivery can suffer.

To answer the OP regarding that chart, you have to look at BOTH the top most row (which dictates the current draw) AND the left most column (which dictates TOTAL length of extension cord). Once you find the current draw on the top-most row, go DOWN that column until you reach the row that is closest to your total extension cord length, Where ever the amp column and cord length row intersect, that is the "optimum" gauge required for the extension cord in order to not suffer heavy voltage losses which will reduce total power delivery at the end of the cord. The power "lost" through the cord ends up as heated copper wiring in the cord itself due to electrical resistance.

[Synchroman]

If you need to go 150 feet to your work site, you really need a generator. For that distance as shown above, you are going to need 6 gauge to use an extension cord. That would be costly.

[raferguson]

To clarify a little bit, every table of this type is built on the assumption of a permissible voltage drop, usually 3%. I went ahead and used the web site below, and cranked in 150 feet, 15 amps, 12 ga, and got a voltage drop of 9 volts, around 7.5%. That is quite a bit, but not crazy. Most likely your grinder does not pull 15 amps continuously. What you would notice is a reduction in the power of the grinder, due to the low voltage. You might also be more likely to overheat or burn out the motor, due to the low voltage.

I would run an experiment, in which I used the grinder with no extension cord, and then used it with the extension cord, and see how noticeable the power loss was. You could also use a voltmeter or Kill A Watt meter to measure the voltage, etc. I would not be real enthused about running power tools below 108 volts, which would be 10% lower than the nominal 120 Volts. For example, for my RV, I will not run the air conditioner below 108 volts.

I agree that a 6 ga cord is probably impractical, but also unnecessary. Using their web site, an 8 ga cord would have a voltage drop of 2.9 %, which should be very acceptable.

http://buyextensioncord.com/info_voltage_drop.shtml

However, what none of these models take into account in the voltage loss in the house wiring. If the outlet is right next to the breaker box, that is probably a minimal voltage drop. But if there is 50 feet of 14 ga wire in the wall, that would be 3.9% voltage drop, not counting the extension cord! That is probably why the table suggests 6 ga cord, rather than the theoretically adequate 8 ga cord. You really need to look at the house wiring, and see how much voltage drop you have there.

If you have a 15 amp circuit, the smart money might be to run a new outlet, fused for 20 amps, but with 10 or 12 ga wire.

I don't think that I am disagreeing with anything that folks have already written here.

[WillieB]

The proof is in the pudding. With your set up, test voltage under full load. If it proves lower than tool rated voltage, you have a bottle neck in your power source. It may not be in your cord. Electrical contractors are forced to compete with the lowest common denominator. If your builder subbed the job to a cheap electrician, or layman, you have a cheap circuit. Wiring may be small, too long, or connections too high resistance. These half hearted connections resisting current will burn down your building.

[ryanjones2150]

Oh ya, that's bad. Let's not do that.

[H2o]

3% loss is under ideal circumstance. I would assume you loose more through possible bad connectors or sometimes, extensions cords. I would assume that some of the super cheap cords could have inferior copper in them as well.

After contractor left our job, i went through and verified every circuit breaker to make sure all was nice and tight. Found a whole bunch of loose connections... some REAL loose.

[freefly23]

Thanks so much for replying guys. I did buy a generator.

So basically you need larger extensions cords at longer ranges to provide the proper voltage, this is the answer I was looking for.

However, why do larger extensions cords provide more voltage than smaller ones? Is this because the electrons have a larger surface area to travel over? If that is the case, can you also have smaller copper strands inside the same guage wire to provide more surface area and therefore voltage?