The purpose of this guide is for user to properly select a fuse which provides protection of components, circuit or equipments. The following flow is considered for fuse selection.

Factors taken into consideration
The safety approvals required for fuse shall be determined according to the safety approvals required on the end product. It is the safety approval that determines initially the selected fuse designed to IEC standard or UL standard.

a. The space limit of circuit in design.
b. Mounting mode.

The voltage rating of the fuse shall be greater than, or equal to the available circuit voltage.

The interrupting rating of the fuse should exceed the Maximum Fault Current of the circuit.

Does there exist "turn-on current" in a circuit when the end product turns on or off? The "turn-on current" is normal for some circuit and requires the slow-blow fuse or medium slow-blow fuse.

The overload current and time in which a fuse must function (It may be specified on the specific protection needs of circuit by design engineer.) Referring to the Time-Current curve, the maximum current rating which meet the requirement would be taken as the upper limit for current rating A1.

a. Steady state current through a fuse (based on the specific circuit).
b. The difference of current rating for fuse designed to IEC standard and UL standard, refer to STEADY STATE CURRENT.
c. Effect of ambient temperature on current-carrying capacity of fuse, refer to AMBIENT TEMPERATURE.
d. Effect of pulse (including surge currents, turn-on currents, in-rush currents and transients) on life of fuse, refer to PULSE.
e. "Turn-on current" and duration should be compared toTime-Current curve of relevant fuseWhen A1≥A2, any rating can be selected from the range of A2 to A1.
When A1＜A2, it is advised to select another type fuse.

The sample shall trial-operate in the actual circuit.

AMBIENT TEMPERATURE
　

PULSE

 Pulse produces thermal cycling and mechanic fatigue which could affect the life of fuse. In design the selected fuse should have a I²T value much greater than the I²T value of pulse. Refer to TABLE A showing the relationship between the life of fuse (the endurable times of pulse shock.) and U ( ratio between pulse I²T value and fuse I²T value ).The I²T value of a fuse presented in this catalog may be for your reference. The I²T value of a pulse can be approximated from the following formulas for a typical wave shape, refer to TABLE B.

TESTING

 In all kinds of electrical protection doubts, contacting our engineers are welcome Possibly we will work with you making some special recommendations to help you solve these problems.