Electrical
Wire Ampacity Calculator
How much current a conductor can carry, after temperature and conductor-count derating.
Result
A planning estimate, not a code calculation. Conductor sizing, overcurrent protection and load calculations are governed by the NEC as adopted and amended where you are, and by the listing of the equipment involved. Have the design confirmed by a licensed electrician and inspected. Ampacity is also limited by the temperature rating of the terminations at both ends, which for most residential equipment is 60 or 75 degrees regardless of what the conductor itself is rated for. Small conductors additionally have fixed overcurrent limits.
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About this calculator
Why does the number of conductors matter?
Each one produces heat, and they all share the same raceway to get rid of it. Beyond three current-carrying conductors the bundle runs hotter and every conductor has to be derated.
Can I use the 90 degree column?
Only for derating calculations. The final ampacity is still limited by the termination rating, which is usually 75 degrees, so you may start from the 90 column but you cannot finish above the 75 value.
The formula
usable ampacity = table value x temperature factor x conductor-count factor
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