If you replace a power cable and thus increase the gauge of a power cable, will more energy automatically flow through the cable to the appliance purely based on the fact the gauge of the power cable has increased and no other factors have changed?

1st you have to define the demarcation point of the appliance. Lets say the appliance is a 60W light bulb. If the gage of the wire is too small, you have made a heater/fuse. So, lets deal with the case of increasing the wire gage (smaller number). Wire has a reistance and that resistance is (p*L)/A. p is the resistivity of the material. L is the length and A is the cross sectional area. You can see from the equation that when L gets bigger, R increases and when A gets smaller R increases. P = (I^2)/R. The appliance (light bulb) will never draw more than I (current). R (resistance)of the cable can be calculated. Thus you can find out how much power is lost in the cable as heat. Contact resistance of screws and plugs also come into play. As the wire gage decreases (smaller #) the appliance gets supplied a slightly larger value of V. I will go up. The appliance will use power more efficiently and the resistance of the cable will drop and thus less power is lost as heat.

Hello toro - You are correct - if you substitute a wire with larger gauge size there should be more total energy used. Recall that the power is calculated using Power = Voltage^2/R; here the voltage at the power panel is constant, and R is the total resistance of the cable and the applicance. By using a larger cable you reduce R, and hence the total power being deliverd is increased.

Simply increasing a wire with a larger gauge will not cause more energy to be consumed, only the capactiy to handle more power will be available.

The answer to the question "will more energy automatically flow through the cable" is no.

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Originally Posted by tkrussell

Simply increasing a wire with a larger gauge will not cause more energy to be consumed, only the capactiy to handle more power will be available.

The answer to the question "will more energy automatically flow through the cable" is no.

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I disagree -- there is in fact an increase in power available to the appliance and an increase in the total power consumed when you increase the gauge size. However, I would agree that in most practical applications the effect is very small, and can typically be ignored.

Let me give an example: consider the case of using 100 feet of 12 AWG wire versus an 18 AWG wire. This may not be a very practical example, but it will make the point. The resistance of the 12 AWG wire is 7.77 ohms/Kft, and the 18 AWG wire is 1.93 ohms/Kft. If these wires are used to connect a 100 watt light bulb (assumed resistance of the bulb = 144 ohms) to a 120 volt power supply, the total power is calculated as follows:

Case 1: Using 18 gauge wire:




Case 2: Using 12 gauge wire:




Thus the power consumed when using 12 gauge wire is about 0.8 watts greater. Not a huge difference to be sure, but it's there.

Taking the calculation one step further - the power consumed by the bulb depends on the voltage of the line at the bulb, which is calculated from:



For the 18 gauge wire this works out to 118.71 volts, and for the 12 gauge wire it's 119.68 volts. If you calculate the actual power consumed by the bulb you find that connecting it with 12 gauge wires means the bulb uses 1.6 watts more than if you connect it with 18 gauge wire.

For power cabling like this the effect is so small that it can typically be ignored. However in other applications the effect can be very significant. Consider for example your home stereo system - one reason for using "Monster" speaker cables, among others, is to increase the power available to your speakers.