Temperature Correction Chart

Use this worksheet after the temperature-correction calculator result to document the ampacity starting point, ambient factor, conductor-count factor, terminal cap, and final usable ampacity.

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Quick reference table

The temperature-correction calculator result is a planning checkpoint, not the final conductor approval. Start with a valid ampacity basis, document the ambient-temperature condition, apply the conductor-count adjustment, then compare the adjusted result with the governing equipment termination limit before carrying a usable ampacity into wire size, OCPD, or load documentation.

Temperature correction result stack

Temperature correction result stack
Worksheet field	Record from calculator	Verification before next decision
Starting ampacity	Lookup or custom starting value	Confirm conductor material, size, insulation, and ampacity basis
Ambient condition	Temperature value and unit	Confirm actual routing condition and any project-required temperature adder
Ambient factor	Temperature correction factor	Keep separate from conductor-count adjustment
Conductor factor	Current-carrying conductor adjustment	Confirm which conductors count in the raceway or cable
Termination cap	Terminal-column or equipment limit	Confirm equipment markings and manufacturer instructions
Final usable ampacity	Lower governing value	Carry forward to load, OCPD, voltage-drop, and documentation review

Field conditions to document before trusting the result

Field conditions to document before trusting the result
Condition	Why it changes the worksheet	What to record
Hot attic, roof, or outdoor routing	Ambient can exceed the assumed calculator value	Location, measured or design temperature, and routing note
Multiple circuits in one raceway	Conductor-count adjustment may control	Count basis and which conductors were treated as current-carrying
90C conductor with lower-rated terminals	Terminal rating can cap the final result	Equipment terminal marking and selected cap
Cable or assembly with product limits	Product instructions can restrict the assumed basis	Manufacturer data, listing, and installation note

Formula basis

Final usable ampacity = min(starting ampacity x ambient factor x conductor-count factor, termination limit).

Starting ampacity is the calculator lookup value or user-entered ampacity before adjustment.
Ambient factor is selected from the conductor temperature rating and the ambient condition entered in the calculator.
Conductor-count factor applies when the current-carrying conductor count requires adjustment.
Termination limit is the equipment connection rating or marking that can cap the final usable ampacity.

Worked examples

Warm raceway with six current-carrying conductorsAfter the calculator returns an ambient factor and a conductor-count factor, record both factors separately before comparing the adjusted ampacity with the terminal cap. The worksheet should show which factor reduced the result.

90C insulation adjusted, 75C equipment terminal checkedUse the calculator output to document the adjustment basis, then compare the adjusted value with the equipment terminal limit. The value carried forward is the lower governing ampacity.

Assumptions. Balanced load and line-to-line voltage assumptions behind this chart.

The worksheet assumes calculator inputs already reflect conductor material, size, insulation rating, ambient temperature, and current-carrying conductor count.
The worksheet does not decide neutral-counting rules, rooftop or field temperature adders, wiring-method permissions, voltage drop, or final conductor selection by itself.
The adopted NEC edition, equipment listing, manufacturer instructions, utility requirements, and AHJ interpretation must be verified before installation.

Code and standard notes. Planning limits that should be checked before final equipment selection.

Use this worksheet as an educational planning record; verify the adopted NEC edition, equipment listing, manufacturer instructions, utility requirements, and AHJ requirements before final conductor selection.

How to use this chart

1Start with the calculator resultCopy starting ampacity, ambient factor, conductor-count factor, termination limit, and final usable ampacity into the worksheet.

2Check the temperature basisConfirm whether the calculator used Fahrenheit or Celsius input, then record the actual routing condition behind that temperature.

3Keep the cap visibleDocument whether adjusted ampacity or terminal limit controls, because that value is carried into the next sizing decision.

Worksheet checklist. Record source basis, review gaps, and assumptions before using the chart result.

Record all factorsWrite ambient factor and conductor-count factor separately so final ampacity can be traced to each condition.
Record the limiting valueLabel the lower governing value between adjusted ampacity and termination ampacity before using it downstream.
Record verification notesAdd equipment marking, product data, conductor count, routing condition, and AHJ review notes next to the calculator output.

Common mistakes to avoid. Review these before turning chart current into an equipment decision.

Using adjusted conductor ampacity without checking whether the selected terminal rating creates a lower final usable ampacity.
Entering ambient temperature without documenting the unit, routing condition, and whether any project-required temperature adder was already included.
Combining all factors into one number without preserving the count basis, temperature basis, and terminal cap for review.

Frequently asked questions

These answers explain how to use the chart without turning a quick reference into a final design decision.

Why does termination rating matter after temperature correction?

A higher insulation rating may be used for adjustment calculations in some workflows, but the final usable ampacity can still be capped by the equipment termination limit.

Can this chart replace a conductor sizing review?

No. It documents one calculator result and should be followed by load, OCPD, voltage-drop, equipment, manufacturer, and AHJ review.

Should ambient factor and conductor-count factor be combined immediately?

Keep them separate on the worksheet first. A reviewer should be able to see whether heat, conductor count, or terminal rating controlled the final value.