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Wire Fusing Current Calculator

Wire fusing current calculator allows you to estimate the approximate DC fusing current for a given wire size and material 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: I_f = C × d^1.5,

where:

I_f – wire fusing current;
C – Preece's coefficient for the particular metal;
d – wire diameter in inches.

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 Questions

How to select safe wire size for a 110 V Household?

Example 1. Kitchen Appliances – Microwave + Coffee Maker

Microwave: 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.