There are four main electrical characteristics that describe a fuse. The voltage rating of a fuse is the maximum system voltage for which the fuse can be used safely to open a circuit. The current rating of a fuse is the nominal amperage value assigned to the fuse, typically established based on a controlled set of test conditions. This is the value of current a fuse can carry during normal operating conditions. The interrupting rating or breaking capacity, is the maximum specified current which the fuse can safely break at the rated voltage. It should be noted that a fuse can have multiple interrupting ratings as well as both AC and DC ratings. The amount of energy needed to begin melting the fuse element is known as melting I²t. With regard to fuses, the term is usually expressed as melting, arcing, and total clearing I²t. The units for I²t are expressed in ampere-squared-seconds [A2s]. I²t has two important applications to fuse selection. This characteristic is often used to determine a fuse’s ability to withstand pulse or transient overcurrent events. It is also used to perform selective coordination with other components in a circuit.