Wire Ampacity Calculator
Ampacity by Wire Gauge
Look up ampacity for standard wire gauges per NEC Table 310.16
Wire Size for Current
Find the minimum wire gauge for a given current
Formula
Ampacity from NEC Table 310.16 | Continuous load: Wire ampacity ≥ 125% × load current | Derating for conduit fill and ambient temperature may apply
Frequently Asked Questions
What is wire ampacity?
Ampacity is the maximum current a conductor can carry continuously without exceeding its temperature rating. It depends on conductor size, material (copper or aluminum), insulation temperature rating, and installation conditions. NEC Table 310.16 is the primary reference.
What is the 80% rule for continuous loads?
Per NEC 210.20(A), conductors for continuous loads (operating 3+ hours) must be rated at 125% of the continuous load current, which means you can only use 80% of the conductor's ampacity. For example, a 20A circuit can only serve a 16A continuous load.
When should I use aluminum vs. copper wire?
Copper has higher ampacity and is more common for branch circuits. Aluminum is lighter and less expensive, making it preferred for large feeders and service entrance conductors (4 AWG and larger). Aluminum requires anti-oxidant compound and compatible connectors.
You may also need
A
Wire Gauge Calculator
Free wire gauge calculator. Find AWG wire specifications including diameter, resistance, and ampacity.
ScienceA
Voltage Drop Calculator
Free voltage drop calculator. Calculate wire voltage drop based on wire gauge (AWG), current, distance, and supply voltage. Determine if your wiring meets NEC standards.
ScienceA
Fuse Sizing Calculator
Free fuse sizing calculator. Calculate the correct fuse or circuit breaker size for your electrical circuit based on load current, wire size, and NEC requirements.
Science