In order to select the right amperage of the fuse, you first need to know the full-load steady-state current of the circuit at an ambient temperature of 25º C (68º F). Once the current value is determined, then a fuse rating should be selected as to be 135% of this value (taken to the next standard value).

What is the difference between UL Class RK1 and RK5 fuses? Class RK1 and RK5 fuses are the same physical size but Class RK1 fuses are more current-limiting than Class RK5 fuses. RK1 fuses can provide better protection because they allow less damaging energy to pass through them while opening (blowing).

The R after the hyphen is a symbol to represent that the particular fuse is a “rejection” type fuse. Their design is slightly different and have higher interrupt ratings than the FRN type fuses.

Classes of Fuses In the case of fuses, these standards have culminated in the establishment of distinct classes of low-voltage (600 volts or less) fuses, Classes RK1, RK5, G, L, T, J, H and CC being the more important.

The speed of a fuse is essentially the time it takes for the fuse to open when a fault current occurs. The speed of the fuse is also known as the time current characteristic of the fuse. Fuse manufacturers usually provide this information in a time current curve chart as pictured.

Advantages of H.R.C. Cartridge fuse over rewirable fuse:  High speed operation.  Ability to clear high values of fault current.  Its operation is silent and without flame, gas or smoke.

Fuses are always connected in series with the component(s) to be protected from overcurrent, so that when the fuse blows (opens) it will open the entire circuit and stop current through the component(s).

Blowing off and breaking the circuit.

Because the fuse can disconnect the circuit only when the excess current flows completely through the neutral. Since, neutral is not a live conductor coming from the source, disconnecting a neutral line can only open the current path through neutral. But, the live phase still carries the charge.

An electric fuse is based on the principle of heating effect of electric current. It is made up of thin metallic wire of non-combustible material. A fuse is always connected between the ends of the terminal in a series connection with the circuit.