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I observed the rebuilding of a 12KW, 120V gas-powered generator. I was amazed at how small the generator portion was (roughly the size of an electric motor you might find in a major home appliance). The windings were pretty thin magnet wire, like you would find in an appliance motor.

Getting the 100A generator output to the breaker box requires heavy-duty wire. That same current originates in the generator windings. How is the thin wire in the windings able to carry 100A (which far exceeds what wire that size is rated for)?

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Note: Small Gauge mean the wire can carry a significant amount of current. Example per the attach AWG 4-5 can carry 100A. There are lot other factors need to be considered before selecting a wire.

Below is guide line help you appreciate wire gauge vs current. This is purely a guideline. I suggest searching American Wire Gauge Charts vs Electrical Current load for additional information. Below are some links for you to get started.

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References:

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  • $\begingroup$ Thanks for catching my mistake in referring to thin wire as "small gauge" (I clarified that in the question). The heavy duty wire used to connect the generator to the breaker box has small gauge numbers. My question is about the generator windings, which use wire of nearly several orders of magnitude smaller cross section. Wire of that size is rated for a tiny fraction of the 100A that flows through it. $\endgroup$
    – fixer1234
    Commented Oct 10, 2019 at 0:13
  • $\begingroup$ @fixer1234 check generator coils: max power given wire gauge I hope this answers your question $\endgroup$
    – Mahendra Gunawardena
    Commented Oct 10, 2019 at 0:37
  • $\begingroup$ Some good information in that answer. It doesn't seem to fully explain it, though. You can use a bunch of parallel windings to split up the current, but that still doesn't get the current per winding close to the ratings of the wire (without cryogenics). I guess what I'm asking is whether there are other physics at play that enable windings in a generator (or I suppose motor) to carry more current than they otherwise could. Or does the fact that it works imply that the generator must have some combination of windings and wire size that results in current being within the wire's normal rating? $\endgroup$
    – fixer1234
    Commented Oct 10, 2019 at 1:26
  • $\begingroup$ Rereading the linked answer, it sounds like the latter is the case. So I guess it answers this question. Would it be preferable to mark this question as a duplicate, or just delete it? And thanks for your help. $\endgroup$
    – fixer1234
    Commented Oct 10, 2019 at 1:32
  • $\begingroup$ Now need to delete, or mark duplicate. $\endgroup$
    – Mahendra Gunawardena
    Commented Oct 10, 2019 at 1:34
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My question was based on an appearance that the thin winding wire seemed to violate the laws of physics, so there might be some other factors at play. Neil_UK answers this in generator coils: max power given wire gauge on the Electrical Engineering site. The bottom line is no. It's mainly a matter of using multiple coils in parallel to manage the current handling requirements per coil. Other factors, like the duty cycle and dissipating heat also come into play.

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