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How To Test Plug Fuses

Testing Plug Fuses Using a Multi-meter

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Testing a Plug Fuse

Testing a Plug Fuse

Photo: Timothy Thiele

What is a Plug Fuse?

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.

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 work bench 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 multi-meter out and place it on your work bench. 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.

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