When the wiring in a house is overloaded with too many appliances drawing current, it overheats and can start a fire in the walls or attic. Old electric panels with round, glass screw-in type fuses use a simple, dependable technology to avoid that problem: a small metal strip, visible through the window in the center of the fuse, is calibrated to overheat and melt apart when amperage (current flow) exceeds the rating on the front of the fuse. If you can’t see the metal strip in the window, that means the fuse strip has “blown” open and shut off the circuit. The flaw is that the wiring for the household circuits in old houses is rated for a 15-amp fuse, but the base that the fuse screws into, called an “Edison base” or “Type T” and similar to one for a light-bulb, will also accept a 20, 25, or even a 30-amp fuse—twice the rated, safe load for the wiring.
Homes that were built with fuse panels in first half of the 20th century had an electric system designed for the expected usage of the times. Just a few circuits were necessary for a refrigerator, range, a couple of fans, and some lighting. But the 1950s began the era of “Live Better Electrically,” and homes acquired TV, hi-fi stereo, a washing machine, dryer, multiple kitchen appliances, and eventually, air conditioning. Homeowners that had a problem with all those appliances repeatedly blowing fuses discovered that replacing the 15-amp fuse that the circuit was rated to handle with a 25 or 30-amp one solved the problem.
