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Is this analogy correct? Think of electricity as water. The source is a big basket full of water, wires are pipes. Turning a switch means opening a pipe; as the water flows it makes the engine turn.

Does this analogy hold?

If it does, why would there would be a problem if an engine draws 30 amp but you only have 20 amp? In the water analogy, the engine simply wouldn't turn. OR maybe the way I should think about it is that if the engine doesn't turn, somehow the water would back up and make a mess?

I'd like an explanation using terminology that even a child can understand, like water.

Manu
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  • you only have 20 amp - you can't "have amps". "amps" in your analogy is the water flow speed in the pipes. – Eugene Sh. Nov 30 '20 at 16:33
  • This is generally a bad analogy, as it breaks down in all sorts of ways. For example, the failure modes are different. Something that attempts to draw 30 amps from a 20 amp supply is a bit of a minor case of a short circuit (more formally it is an overload), and there isn't a great correspondence with water - valve wide open with only a trickle coming out doesn't really capture the stress on the source from the corresponding electrical case. That water case would kind of be like that of an overload-protected supply, eg something that is a voltage source until a current limit kicks in. – Chris Stratton Nov 30 '20 at 16:35
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    Baskets usually have holes so, not a good analogy. Also water falls with gravity and you haven't mentioned a height differential to drive the water system. – Andy aka Nov 30 '20 at 16:39
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    "Draw 30 amps" means you open the tap enough so that 30 litres of water go through every second. But if your pipe isn't big enough, or your pump isn't big enough, you won't get 30 litres per second, no matter how much you open the tap. Also the pressure will drop to 0 if you try – user253751 Nov 30 '20 at 17:24
  • @Andyaka: There's a reservoir of water up in the sky. Can we make the analogy now? – Manu Nov 30 '20 at 19:19
  • @user253751: OK but I still don't get why the system breaks/burns/etc in terms of water. – Manu Nov 30 '20 at 19:20
  • @Manu The "system" doesn't break, one of the parts breaks. The pipes may overheat and burn because the water is flowing too fast (okay, that doesn't happen with water, but it does with electricity). Or the pump may break because it's overloaded. – user253751 Nov 30 '20 at 19:26
  • You "only have 20 amps" because your generator is not capable of supplying more than 20 amps without falling out of compliance. If you model such a source by mean of an internal resistance that will put a limit to the maximum current you will see that voltage will not be constant. If you accept this electrical model, then you can translate it into hydraulics by placing a pipe of l section at your pump/reservoir exit. – Sredni Vashtar Nov 30 '20 at 20:14

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