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Wiring Fundamentals: Current

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00:00 - Current is a measure of the number of electrons flowing through a wire past a fixed point, per second.
00:06 Linking to our plumbing analogy again, this is equivalent to the physical mass of water we have flowing through our pipe.
00:12 For example if we have our tap fully open and therefore have a difference in pressure of 60 psi across our pipe, we could expect this to be around 25 litres per minute.
00:22 Similarly back in the electrical world, when we connect one end of our wire to the positive battery terminal and the other end to the negative battery terminal, the applied 12 volts difference in electrical pressure will cause electrons to flow.
00:35 Once again this sounds relatively simple, but there are a couple of subtle points that are important to grasp.
00:40 As explained when we talked about voltage, flow, be it electrons or water, only occurs when we have a difference in pressure.
00:47 This concept works both ways however, and it is equally true that we will only have a difference in pressure if we have flow.
00:54 This is why when we connect one end of our wire to the positive terminal of the battery, and leave the other end unconnected or floating, we will measure the same 12 volts at any point along the wire.
01:05 Another important concept to grasp is that current always flows in a loop.
01:09 Electrical circuits are called circuits for exactly this reason.
01:13 It's like a race circuit.
01:15 There is a start, finish line, which is the element in the circuit that supplies the electrical pressure.
01:20 Typically in our automotive world, this will either be the vehicle's battery, or the alternator.
01:25 When you're reading or writing documentation, current has a unit of amperes, or amps, and a symbol of either a capital I, or a capital A.

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