The symbol of a fuse is one of the most commonly used elements in electrical and electronic diagrams. Fuses are used in electronics involving a few volts, as well as in low voltage (120/220V) circuits, and are even employed in medium voltage (over 13,000V) and high voltage (over 60,000V) systems.
This article showcases some of the most common symbols used to represent a fuse.
We recommend the following Excel file, which contains transformer calculations and suggests the minimum and maximum allowable fuses according to the Mexican standard NOM 001 SEDE 2012. This file is available on the Hotmart platform. But it’s in Spanish.
For this reason, the symbol for a fuse can vary based on the voltage used, the application it will serve, and its internal function. Therefore, various symbols may be used to describe a fuse.
The key aspect is to describe the fuse in the schematic by indicating its main characteristics, such as amperage, operating voltage, and type of fuse.
A fuse is an electrical and electronic component designed to protect various equipment. If the fuse’s rated amperage is exceeded, the fuse opens and power is cut off.
Example of a Fuse Symbol
The following image shows a fuse that opens the circuit when the current exceeds 20 A.
The fuse will open the circuit when the nominal amperage is surpassed, thereby preventing excess current from flowing through the protected component.
A fuse is calibrated for the device it protects, so selecting the appropriate one is crucial.
For instance, if a device supports 20 amperes and a 30 A fuse is used, the fuse is not protecting the device. Unless the device has sudden surges—i.e., it briefly draws more than 20 A when starting up but then stabilizes at 20 A.
Sometimes, it is better to use circuit breakers instead of fuses, as circuit breakers only open the circuit and can be reused. In contrast, a fuse must be replaced after it opens.
How to Select a Fuse
A fuse is selected based on the amperage of the device to be protected. A margin is generally provided for startup surges or slight variations.
For electrical transformers, according to the Mexican standard NOM 001 SEDE 2012, the maximum allowable fuse should be 300% of the nominal capacity of the transformer.
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