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quogueelectric:
In so many of the discussions on this forum questions are asked without the author doing adequate initial analysis, measurements, and providing definitions and assumptions that it is hard to converge on useful answers. Similarly many answers are provided without providing supporting measurements or analysis, and also the problem of definitions and assumptions.
I think, but I do not know, that the original intent of this thread was --- How can I provide a simple explanation to a potential customer of why they should pay for the extra cost of using #12 instead of #14?
Most customers have no ability to understand the technical implications of one electrical design vs another.
Consider flickering lights, meaning a light momentarily dimming from some high inrush current when something turns on like an air conditioner. I have this problem from my neighbor's air conditioner. There is nothing I can do about the source of the problem, the pole transformer, except try to get the power company to install a larger lower impedance transformer. There is no valid reason for them to do this. Thus, I live with the problem. There is no wiring solution in my house to solve the problem. I could install a constant voltage transformer, or a motor generator, or some other possibilities. Most of these would be very costly, and might waste a lot of power, like the constant voltage transformer or a motor generator. Note: constant voltage transformers run very hot and are thus not efficient. Even a standard transformer has a moderate power loss. Today there is virtually no reason to use a constant voltage transformer except in some special applications.
Next suppose within my house I have a circuit that feeds a radial arm saw and on this same circuit I have an incandescent lamp to see my saw work. Make the circuit 100 ft of #12 Romex, 0.318 ohms. My light will dim greatly when the saw starts. Assume the main panel has a voltage drop of 0.8 V for a 12 A load, and inrush is 80 A. Thus, at the panel the voltage should drop about 5.3 V. If my light is on a separate circuit from the main panel, then I will get a noticeable flicker, but not severe. In this application I can do something to solve my problem, use the separate circuit from the main panel.
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