Wire Gauge Ampacity Calculator
Copper Wire Ampacity
Find ampacity for copper conductors by AWG gauge
Aluminum Wire Ampacity
Find ampacity for aluminum conductors by AWG gauge
Voltage Drop by Gauge
Calculate voltage drop for a given wire gauge and length
Formula
Voltage Drop = 2 x Length x Current x Resistance / 1000 | Continuous Load = Ampacity x 0.80
Frequently Asked Questions
What is wire ampacity?
Ampacity is the maximum current a wire can safely carry continuously without exceeding its temperature rating. It depends on wire gauge, insulation type, and installation conditions. NEC Table 310.16 provides standard ampacity values.
Why is the 80% rule important for wire ampacity?
The NEC requires that continuous loads (running 3+ hours) not exceed 80% of the wire's ampacity rating. This provides a safety margin to prevent overheating. For example, a 20A-rated 12 AWG wire should carry no more than 16A continuously.
What is the difference between copper and aluminum wire ampacity?
Aluminum wire has about 61% of the conductivity of copper, so it has lower ampacity ratings for the same gauge size. You typically need to upsize aluminum wire by 1-2 gauge sizes to match copper ampacity.
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