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Category Electronics

Total Power (Watts)

System Voltage (Volts)

Current Draw

0.00 A

Rec. Fuse Size--
Based on +25% safety margin

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About

Determining the correct current draw is the first step in safely wiring any electrical device, from automotive accessories to home appliances. This calculator solves for Current (I) when the Power load (W) and System Voltage (V) are known. Overestimating current leads to wasted copper; underestimating it leads to melted wires and fire hazards.

Beyond simple math, this tool integrates a safety logic database to suggest the Next Standard Fuse Size. Industry standards typically recommend a safety factor (often 125% of continuous load) to prevent nuisance blowing while ensuring the fuse fails before the wire does.

Formulas

Current is calculated using the Watt's Law variation:

I = PV

The Recommended Fuse Size is determined by applying a safety margin:

I_fuse ≥ I_load × 1.25

The tool then rounds this value up to the nearest available standard fuse integer.

Reference Data

Standard Fuse Rating	Color Code (ATO/ATC)	Max Continuous Load (Rec.)
1 A	Black	0.8 A
2 A	Gray	1.6 A
5 A	Tan	4.0 A
10 A	Red	8.0 A
15 A	Blue	12.0 A
20 A	Yellow	16.0 A
30 A	Green	24.0 A

Frequently Asked Questions

Fuses are thermal devices. If you run a 10A fuse at exactly 10A continuously, it will get very hot and eventually fatigue or blow. The NEC (National Electrical Code) and other standards recommend sizing fuses at 125% of the continuous load to ensure longevity and reliability.

No, this tool specifically calculates Current and Fuse size. Wire sizing (AWG) depends on current AND the length of the wire (voltage drop), which requires a separate calculation.

Use with caution. AC motors have a "Power Factor" and high startup surge currents. This calculator assumes a simple resistive DC load. For motors, you generally need "Slow Blow" fuses and should consult the motor's nameplate data.