Why is it unwise to install a 20-ampere fuse in the place of a 5-ampere fuse?

Using a 20-ampere fuse in place of a 5-ampere fuse is particularly unwise because the purpose of a fuse is to protect the circuit by breaking the connection when the current exceeds a certain limit. A fuse is rated to allow only a specific amount of current to pass through it; if the current exceeds this rating, the fuse should blow, interrupting the circuit to prevent damage.

If a larger fuse is installed, such as a 20-ampere fuse, it would not blow until the current reaches 20 amperes, which is significantly higher than the 5 amperes for which the circuit components are rated. Consequently, if a fault occurs or an overload happens, excessive current can flow through the circuit for a longer duration before the larger fuse eventually blows. This excessive current can generate heat in the wiring and components, possibly leading to electrical fires, overheating, or damage to the equipment.

In contrast, a correctly rated fuse would blow at 5 amperes, safely stopping the flow of electricity before any damage occurs. Therefore, using a higher-rated fuse like the 20-ampere can create hazardous conditions that a 5-ampere fuse is designed to protect against.