How to choose the right fuse

Written by g.k. bayne
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Electrical and electronic devices all need some type of protection, which typically comes from fuses. Unlike circuit breakers, a fuse is a one-time protection that must be replaced after serving its purpose. Fuses range from small glass tubes to large main electrical-service equipment. Generally fuses are rated on the voltage they can control, speed of interruption and their size. Listed in the resources is a chart for applying those ratings to your particular application. Identifying a methodical approach is still needed for choosing any type of fuse, whether it is a replacement or for a new application.

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  1. 1

    Identify the type of voltage that is being protected. Fuses are rated not only by the amount of voltage but whether it is direct current (DC) or alternating current (AC). Some fuses may be dual-rated---able to handle both DC and AC power. These ratings however will be different in the overall power that can be utilised for proper protection. Select a fuse that will fall into the voltage range of that particular circuit.

  2. 2

    Observe the amperage of the electrical circuit that the fuse will be protecting. Circuits that include motors or fluorescent lighting use wire coil windings. When starting, these coils of wire will have an "inrush" of current. This inrush will be greater than the actual power bring used once the device is running. Pick a fuse made for motor-starting or one that has a time-delay rating. This will allow the electrical load to be protected while the inrush current may exceed the fuse's overall interruption rating.

  3. 3

    Size the fuse to its particular holder. There are specific fuse holders that will only physically connect to that type of fuse. These fuse-connection points are constructed not only so they will fit into a particular space but also for the fuse's characteristics. Small glass-tube fuses can only be replaced with those of like kind. Special time-delay fuses have a certain diameter and length. Other types of fuses of the same voltage and rating will not fit in that particular holder. Large knife-blade fuses that control high voltage and amperage cannot be replaced with fuses of a lesser capability.

  4. 4

    Inspect the fuse for internal element replacement. Some fuses carry an internal replaceable fused element. These pieces of electrically conductive metals are made to be withdrawn from a cylindrical container after they have "blown." A metal fuse strip is then placed back into the round cartridge and the circuit can be reset for power. Generally these fuse elements are sold in separate boxes and are rated in the same way as a one-time fuse.

  5. 5

    Use a fuse that has an inspection window. These windows will indicate whether or not the fuse has "blown." This type of fuse can be extremely helpful in industrial applications or for the home setting. A quick visual check is all that is needed for identifying a problem with electrical circuits.

Tips and warnings

  • When checking fuses with an ohmmeter, pull the fuse from its holder before using the meter. There will still be voltage applied to one side of the fuse.
  • Fuse-pullers should always be used when servicing larger fuses of any kind. Fuse-pullers are insulated and will protect the user from shocks.

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