MeepMeep asked a question about fusing circuits in my "project fuse box" thread.
This new thread will include more detail.
First, to have a circuit you need at least three items.
A voltage source
A current carrying conductor
Two more items are very nice to have
A way to turn it off and on (switch)
Circuit protection (fuse)
Below is the simplest form of a circuit with a 12v battery, fuse, conductor, switch and a 1/2 ohm load.
1. The first circuit is switched off, no current will flow.
2. The second circuit is switched on; current is flowing through the circuit at a rate of 24 amps. The fuse that is chosen should be at least 5 amps higher than the highest current the circuit will flow so I chose a 30 amp fuse which is the closest available without being less than 5 amps.
3. This circuit has an (open) failure. Opens can be in the wiring, connections, load etc. I put the open in the load. A circuit with an open does not operate but does not blow a fuse as there is no way for current to flow. If you have a circuit that is not working on your scoot and you checked all fuses only to find that they are all ok, you have an open somewhere. Switches create opens, so make sure a switch is not flipped to the off position.
4. This circuit has a (short to ground) failure. A shorted circuit usually bypasses only part of the load. Since half of this circuits load is shorted, the new resistance of the circuit is only .25 ohm and that will cause the circuit to attempt to flow 48 amps. Since the circuit is protected with a 30 amp fuse, the fuse will burn in two and save the wiring from over current failure.
5. This circuit is grounded. When we use that term it usually means the entire load is bypassed. This type of failure will try to flow the maximum amount of current that the conductor can handle. Since your scooters battery is capable of flowing more current than even the largest conductor on your scooter can safely handle, the conductor will overheat, burn the colored insulation off and possibly either blow in two or get so hot that it can start a fire if it comes in contact with something combustible.... But since we have a 30 amp fuse protecting the circuit, the fuse will burn in two protecting the wiring once again.
I kept this simple and there can be other forms of failures that can cause a circuit to operate improperly such as shorts to power, high resistance connections such as loose or corroded terminals but neither of those will blow a fuse.