Now would be a good time to discuss fuses and circuit breakers, which are collectively called circuit protection devices (CPDs).
Circuit protection is the intentional installation of a “weak link” in an electrical circuit.
(Source - Blue Sea Systems)CPDs are designed to interrupt a circuit when the electricity flowing in the circuit approaches damaging or dangerous levels. When the amount of amps in the circuit approaches the CPD's rating, the CPD opens (breaks) the circuit, stopping the flow of electricity.
CPDs are used in three basic ways:
1. To protect devices (loads), such as sensitive electronics, from being subjected to electrical current greater than they are able to handle. (Few things "make your day" quite like an expensive device emitting noise and smoke to indicate it's destined for the junk pile.)
2. To protect wire and connection components from an electrical overload that could cause them to heat up, melting and possibly igniting the insulation. In extreme cases, the generated heat could be enough to cause the metal wire to melt.
3. To protect from electrical short circuits.
The first two rarely happen in properly designed and well made circuits. When they do occur, it's usually due to either excessive resistance in the circuit or a short circuit somewhere.
An electrical short circuit is a shortcut across a circuit that provides an easier path for the electricity to follow back to the circuit source, bypassing the circuit load. The red line in the following diagram modifies our Basic Electrical Circuit diagram to demonstrate an electrical short.
And, the following diagram shows the same thing in a common ground circuit like those found in motor vehicles. (I also added plus and minus symbols to more closely demonstrate the actual circuits.)
