Wiresize is expressed in gauge number—the common standard being the American WireGauge (AWG)—whereby a smaller gauge number corresponds to a larger-diameterwire (high current capacity).

Example: Why shouldn’t you connect a wire across a voltage source? For example, ifyou connect a 12-gauge wire directly across a 120-V source (120-V mains outlet), whatdo you think will happen? What will happen when you do this to a 12-V dc supply,or to a 1.5-V battery?Answer: In the 120-V mains case, you will likely cause a huge spark, possibly meltingthe wire and perhaps in the process receiving a nasty shock (if the wire isn’t insu-lated). But more likely, your circuit breaker in the home will trip, since the wire willdraw a huge current due to its low resistance—breakers trip when they sense a largelevel of current flowing into one of their runs. Some are rated at 10 A, others at 15 A,depending on setup. In a good dc supply, you will probably trip an internal breaker orblow a fuse, or in a bad supply, ruin the inner circuitry. In the case of a battery, there isinternal resistance in the battery, which will result in heating of the battery. There willbe less severe levels of current due to the internal resistance of the battery, but thebattery will soon drain, possibly even destroying the battery, or in an extreme casecausing the battery to rupture.