When specifying the use and application of any safety or protective device, it is obviously essential, particulary from a liability standpoint, that the terminology used is both correct and fully understood. This section briefly explains the most commonly used terms associated with electronic fuses.
The temperature of the surrounding medium which normally comes in contact with the fuse. The medium is usually air. The current carrying capacity tests of fuses are performed at 25C and will be affected by changes in ambient temperature. A fuse runs hotter as the normal operating current approaches or exceeds the current rating of the selected fuse. Practical experience indicates fuses at room temperature (25C) should last indefinitely if operated at no more than 75% of fuse ampere rating. The fuse ambient temperature is significantly higher in many cases, because it is enclosed or mounted near other heat producing components, such as resistors, transformers, etc.
CHART SHOWING EFFECT OF AMBIENT TEMPERATURE ON CURRENT-CARRYING CAPACITY