⚡ Fuse Size Calculator
📘 About this calculator: The fuse size calculator precisely determines the correct fuse rating protecting electrical circuits against overcurrent. Based on international standards (NEC, IEC 60269), it applies load type multipliers (continuous, motor), ambient temperature derating, and conductor bundling factors. The result recommends a standard fuse size to prevent nuisance blowing while ensuring safety. Accurate for residential, industrial, and automotive applications worldwide — with dynamic graph visualization.
📊 Fuse Sizing Comparison
For loads lasting 3+ hours, fuse rating must be at least 125% of continuous current. This prevents overheating and nuisance tripping.
Motor branch fuses: max 175% for time-delay fuses. Our 175% factor approximates safe motor starting without nuisance blowing (worldwide IEC allows similar).
Higher temperatures reduce fuse current-carrying capacity. Use correction factors (NEC Table 310.15(B)(2)(a)). Global standards use comparable de-rating.
Multiple current-carrying conductors in a raceway reduce heat dissipation. Derating factors based on NEC table 310.15(C)(1).
Our rounding uses global preferred fuse ratings (IEC 60269 / UL). Final fuse size respects IEC ‘gG’ characteristics and common worldwide ampere classes.
Result rounds up to nearest standard value: 1,2,3,4,5,6,8,10,12,13,15,16,20,25,32,40,50,63,80,100,125,150,175,200,225,250,300,350,400A.