A plug fuse has a round, screw-in base that looks much like a light bulb base. The outer threaded part is one contact point for the fuse and the bottom of the fuse is the other. A fuse link is visible through the visible pane in the top of the fuse.
Plug fuses come in three different types: standard, tamper-resistant (Edison-based), and time-delay fuses. The standard and time-delay fuses have larger bases. Any sized fuse of these type can be screwed into these fuse sockets. It's a bad design because you can actually screw a 20 or 30-amp fuse into a 15-amp socket.
Tamper resistant fuses have a smaller, plastic screw-in base that is accepted into the fuse socket via a fuse adapter. These adapters are specially designed to only accept the right amperage fuse into the socket. Although you can screw a 30-amp fuse into a 15-amp socket, the center contact point will not be reached, thus the fuse will not make contact. Only the appropriate amperage fuse will work for this socket.
Plug fuses have a metal alloy ribbon inside that carries the current of the circuit. In the case of a short or overload, causing too much current to flow, the ribbon will melt and open the circuit. When this happens, no current can flow and the circuit is disconnected from the power supply. This protects against short circuits and overloads that may damage electrical wiring and cause house fires.
Removing a Plug-type Fuse
In order to test a plug fuse, you must first remove the fuse from the electrical panel. Grab the fuse and twist it counterclockwise. Unscrew it out of the electrical panel. Stand to the side of the panel when removing it. Now remove the fuse and set the fuse on a table or workbench for easy testing. It is advised to wear safety glasses when doing any electrical work to protect your eyes from flying sparks or an electrical flash.
How to Test a Plug Fuse
In order to test a plug fuse, get a multimeter out and place it on your workbench. Turn on the tester and turn the dial to ohms on a lower setting. Place one lead in each hand and touch one lead to the side of the fuse. Now, touch the other to the bottom tip of the fuse. If the fuse is good, the tester should have little or no resistance showing on the meter. If the fuse is bad, you'll see an infinite reading, meaning the fuse link is blown.
You've heard the term blown fuses, but what is this exactly? First, you need to know what fuses are and just exactly what they are designed to do. You see, your home's electrical wiring must be protected from short circuits and circuit overloads. A fuse incorporates a fuse link that has a specific amperage rating, usually 15, 20, or 30 amps.
Without a fuse or circuit breaker with this specific rating, there would be nothing to protect the wiring, devices, or the operator running things like power tools. Just as the wiring is sized specifically for the load it can handle without breaking down and heating up, so works the fuse. This type of protection is in place to keep your home from having an electrical fire.
If you have an older style fuse panel with standard plug fuses and want to add tamper-proof fuses, simply add plug fuse adapter. These adapters come in 15, 20, and 30-amp sizes. They allow the newer and safer "S" type tamper-proof fuses to be screwed into the standard bases. simply screw the new "S" type fuse into the base and then screw the whole assembly into the fuse panel socket. Each of these plug fuse adapters is rated for either 15, 20, or 30 amps and is labeled on the inner base of the adapter.
Too often fuses are wrongly replaced and many electrical fires are the result. For your safety, only replace fuses with the appropriately sized fuses. If they are blowing, there is a problem with the circuit or something attached to it.