Electrical reference chart
Ampacity Chart
Use this ampacity chart after the calculator result to explain the usable ampacity number, especially when insulation temperature, terminals, ambient heat, or conductor grouping changed the outcome.
Quick reference table
Ampacity is the current a conductor can carry under the installation conditions without exceeding its temperature limit. Use the calculator and planning worksheet to keep the useful field value visible: the lower of the adjusted conductor ampacity and the equipment termination limit, with manufacturer data, adopted NEC rules, and AHJ review kept in the record.
Ampacity result breakdown
| Layer | Record in worksheet | Field meaning |
|---|---|---|
| Base conductor | AWG or kcmil size, copper or aluminum, insulation family | Provides the starting conductor heat rating |
| Ambient correction | Expected surrounding temperature and location condition | Reduces usable ampacity when heat is higher than the base condition |
| Conductor grouping | Current-carrying conductors in raceway or cable | Can require adjustment before comparing to the load |
| Termination cap | 60 C or 75 C equipment terminal basis where applicable | Can be lower than the conductor insulation rating |
| Equipment instruction | Listed equipment, cable assembly, or manufacturer limit | May be more restrictive than the planning screen |
When the ampacity calculator result needs a second look
| Observed result | Likely issue | Review next |
|---|---|---|
| 90 C insulation still limited | Terminal temperature basis is lower | Check equipment lug ratings and conductor material allowed |
| Large derating reduction | Many current-carrying conductors or hot location | Review bundling, raceway count, and installation layout |
| Ampacity passes but wire grows | Voltage drop or future capacity controls | Open the wire size or voltage drop chart before changing size |
| Cable assembly selected | Assembly listing may set its own limits | Use manufacturer data and project specifications |
How to use this chart
Read the result in layers
Compare base ampacity, adjusted ampacity, and termination ampacity separately so the controlling limit is visible after the calculator runs.
Match the real installation
Record raceway type, cable assembly, ambient temperature, conductor count, and equipment terminal rating before relying on a usable ampacity number.
Route wire sizing separately
If the ampacity result passes, still check voltage drop, equipment instructions, and branch-circuit planning before treating the conductor size as settled.
Formula basis
Usable ampacity screen = lower of adjusted conductor ampacity and equipment termination ampacity.
- Base ampacity begins with conductor material, size, and insulation temperature family.
- Adjusted ampacity applies ambient correction and conductor-count adjustment where the installation requires it.
- Termination ampacity is the equipment lug or terminal temperature limit that can cap the final planning value.
Worked examples
90 C conductor on 75 C equipment
The calculator can use the 90 C insulation value for adjustment math where allowed, but the final usable ampacity may still be capped by the 75 C equipment terminal basis.
Crowded raceway in a warm area
A conductor that looked adequate in a simple lookup can fail the usable ampacity screen after ambient correction and conductor-count adjustment are applied together.
Related calculators
Wire Ampacity Calculator
Calculate conductor ampacity with temperature correction, conductor-count adjustment, and 60°C or 75°C termination checks
Cable Ampacity Calculator
Calculate cable current carrying capacity with temperature and bundling corrections per NEC
Wire Size Calculator
Calculate NEC-style wire sizes from load current, ampacity basis, and voltage-drop targets
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Frequently asked questions
These answers explain how to use the chart without turning a quick reference into a final design decision.