Odd Electrical Question

[GallenH]

For those of you with electrical knowledge. You have a corded power tool whose cord is 14guage and a short extension cord, also 14guage. You add a 20' extension cord between the above 2. If the extension cord is 12guage will the circuit have less resistance than if it were 14guage? Or do the 14guage power tool cord and the short 14guage extension cord effectively throttle down any gain?

I'm adding an "extension cord" to my portable solar setup.

Thanks.

 

[booster]

For those of you with electrical knowledge. You have a corded power tool whose cord is 14guage and a short extension cord, also 14guage. You add a 20' extension cord between the above 2. If the extension cord is 12guage will the circuit have less resistance than if it were 14guage? Or do the 14guage power tool cord and the short 14guage extension cord effectively throttle down any gain?

I'm adding an "extension cord" to my portable solar setup.

Thanks.

All the resistances of the individual cords add together, so making one larger and with less resistance will make the total resistance lower than if the larger cord was the same as the rest. This will make for slightly lower voltage drop in the line.

 

[GallenH]

Thanks, booster.

 

[Hatteras Jim]

What booster said -- and keep connections (plugs and receptacles) to a minimum as well. Each set adds a little more r's (not so much when they are new.)



This is probably way too much info, but it may help you down the road:



The voltage drop is dependent on the amount of current flowing from your solar panel to your device. E (voltage) = Resistance X Current (in amps). 14 ga wire (copper) has a nominal resistance (from my chart) of .00257 ohms per foot. In a 30 foot run of 14 ga wire your resistance would be ~.077 ohms. 12 ga wire has a resistance of .0016 ohms per foot or ~.048 ohms in a 30 foot run.



If your device is consuming 1 amp of current, your voltage drop across 30 feet of 14 ga wire would be .077 volts (77 millivolts) E=1 amp X .077 ohms). With 12 ga wire it would decrease to a theoretical loss of .048 volts or 48 millivolts. You would have to determine if a savings of 29 millivolts (77-48 is worth the upgrade.


You didn't say how much current is flowing ("into the tool") or what you are powering, which is the key to the amount of voltage drop across a cable.



If your tool is using 15 amps (max for 14ga) your voltage drop is now 1.15 volts (E = 15 amps X .077ohms). For 30 feet of 12 ga, your loss at 15 amps is now .72 volts. This is now getting significant. (1.15V vs. .72V) There are other factors too: heat, number of wires in a bundle, stranded vs solid, type of conductor used etc.



Sorry, I tried to keep it simple. When in doubt, bigger is better.

 

[cbrown3822]

I don’t believe that this is entirely correct. Think of amperage instead of resistance. All of the amperage on the circuit is passing through the 14 gauge cord so you are limited by the rating of that cord. Reduce it to the ridiculous. If you had a two gauge wire attached to a 20 gauge wire all the current passes through the 20 gauge wire. That is your choke point.

 

[booster]

I don’t believe that this is entirely correct. Think of amperage instead of resistance. All of the amperage on the circuit is passing through the 14 gauge cord so you are limited by the rating of that cord. Reduce it to the ridiculous. If you had a two gauge wire attached to a 20 gauge wire all the current passes through the 20 gauge wire. That is your choke point.

There are two different things going on in this case and with all wiring.


The cord rating is normally to prevent the conductors from overheating in the cord at full rated. Shorter and longer cords will often have the same current rating unless they are on a cord reel as then the heat gets trapped and they derate them.


The other thing is voltage drop and that can determine if your given appliance will run based on the lower voltage, or not, or maybe overheat the appliance. Short cords have proportionately less voltage drop than longer ones of the same rating.


If you strung together 500 feet of 14ga cord and tried to run it at full rated of 15 amps per cord, there would be lots of stuff that wouldn't run from voltage drop at the higher end of rated amps. String together 500 feet of #2 with 6" at the end and you likely would be just fine at the 14ga rated 15 amps.


So if the OP is trying to run 15 amps, and the voltage drop isn't too much, he will be fine, but not more than 15 amps, but if the core were all 14ga, he could get in trouble from voltage drop.

 

[cbrown3822]

Well thought out reply, technically correct. Based on what he describes, however, I was going for a practical application.

 

[RossWilliams]

Most tools have a chart to tell you what gauge extension cord you will need for various lengths of extension cord. Basically the gauge wire on either side is irrelevant. There is no throttling effect. The voltage drop from the 12 gauge cord will just be in addition to any drop from the 14 gauge.