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Wire Fusing Current CalculatorBefore a copper trace or cable catches fire, it hits an absolute threshold where the metal liquefies and breaks the circuit. This online wire fusing current calculator allows you to estimate the approximate DC fusing current for a given wire size and material (Copper, Aluminum, Iron, etc.) according to the Preece's Law. Preece's Law states that the DC fusing current for a straight wire generally depends upon it's diameter: If = C × d1.5, where:
If – wire fusing current; This calculator also allows you to determine the wire diameter for a given material and fusing current. You might also find helpful: Wire Resistance Calculator. Frequently Asked QuestionsWhat is wire fusing current? Wire fusing current is the critical electrical threshold where the heat generated by current density exceeds the thermal dissipation capabilities of the wire, forcing the metal conductor to instantly melt and open the circuit. It represents the absolute physical failure point of a bare or insulated wire.
Does wire insulation affect the calculated fusing current? The melting point of the metal core (e.g., 1085 °C for copper) stays the same, but the insulation material dictates safe operating limits. Standard PVC insulation melts at just 105 °C. This calculator computes the metal fusion point, meaning the wire insulation will typically smoke, char, and catch fire long before the metal hits the calculated fusing threshold.
Can I use this calculator to design a reliable backup fuse for a circuit? Yes, but you must apply a generous safety margin. Because manufacturing variances in copper purity and ambient humidity alter heat dissipation, structural engineers never run wire traces close to their fusing limit. A reliable circuit trace should operate at no more than 30% to 50% of its calculated fusing current.
How to select safe wire size for a 110 V Household?Example 1. Kitchen Appliances – Microwave + Coffee MakerMicrowave: 1200 W ÷ 110 V ≈ 11 A Coffee machine: 800 W ÷ 110 V ≈ 7 A Total load ≈ 18 A If you check with the calculator using Copper, Diameter = 0.08 in (≈ AWG 12), you’ll see this wire safely supports the load. Result: AWG 12 is correct, while AWG 14 (≈15 A limit) would be too weak. Example 2. Small Water Heater (1500 W)1500 W ÷ 110 V ≈ 13.6 A Inputting Copper, Diameter = 0.064 in (≈ AWG 14) shows it can barely handle the current. The calculator confirms that moving to AWG 12 provides a safer margin. Result: AWG 14 is at the limit, AWG 12 recommended. Example 3. Garage Air Compressor (2000 W)2000 W ÷ 110 V ≈ 18 A When checking AWG 14, the calculator shows it fails (≈15 A). Switching to AWG 12 ensures the wire won’t overheat. Result: Always size up to AWG 12 for heavy tools. |
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