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WorksheetCode-sensitiveLast reviewed April 29, 2026

Electrical reference chart

Wire Insulation Reference Chart

Use this worksheet after ampacity and cable calculator results to record insulation type, temperature rating, location suitability, conductor material, and calculator assumptions tied to the result.

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Quick reference table

Wire insulation marking is an input record for ampacity, temperature correction, and location review. Record the exact conductor or cable marking, temperature rating, wet/dry/damp or raceway condition, conductor material, terminal limit, and manufacturer data before using the calculator ampacity result as a project value.

Insulation reference worksheet

Insulation reference worksheet
Worksheet fieldRecord from label or calculatorVerification note
Insulation typeTHW, THHN, THWN-2, XHHW, XHHW-2, USE, USE-2, or project typeConfirm product marking and listing
Temperature ratingCalculator-selected ratingConfirm conductor marking and equipment terminal basis
Location suitabilityWet, damp, dry, raceway, tray, or burial contextConfirm wiring method and product instructions
Conductor materialCopper, aluminum, or CCA as applicableConfirm terminal marking and manufacturer instructions
Ampacity resultBase, adjusted, and final ampacityConfirm derating, terminal cap, and product limits

Insulation review triggers

Insulation review triggers
TriggerWhy it mattersWhat to verify
Wet or damp routingNot every marking fits every locationProduct marking, wiring method, and manufacturer instructions
High ambient conditionTemperature rating affects adjustment basisTemperature correction worksheet and terminal cap
Cable assembly instead of individual conductorsAssembly instructions can control useCable listing, installation method, and product data
Direct burial or service entrance useApplication may require specific product ratingProduct marking and AHJ review

Formula basis

Insulation review = insulation type + temperature rating + location rating + conductor material + terminal limit + calculator ampacity result.

  • Insulation type is the marking or cable assembly type entered in the calculator.
  • Temperature rating is the conductor insulation rating used for ampacity or derating inputs.
  • Location basis records whether the wiring method and product rating fit the actual wet, dry, damp, raceway, tray, or burial condition.
  • Terminal limit records the equipment connection rating that can cap final ampacity.

Worked examples

THHN/THWN-2 feeder reviewRecord the full insulation marking, selected calculator rating, wet-location assumption, terminal limit, and final adjusted ampacity before using the result in project notes.
Cable assembly with product instructionsIf the calculator result came from a cable ampacity screen, attach the cable type, installation condition, and manufacturer data to the worksheet before treating the ampacity as reusable.
Assumptions. Balanced load and line-to-line voltage assumptions behind this chart.
  • The worksheet assumes the conductor or cable product marking is available before final selection.
  • The worksheet does not approve a wiring method, wet-location use, direct burial, service entrance use, or terminal compatibility without product and equipment verification.
  • The adopted NEC edition, product listing, manufacturer instructions, equipment markings, utility requirements, and AHJ requirements must be verified before final installation.
Code and standard notes. Planning limits that should be checked before final equipment selection.
  • Use this worksheet as an educational planning record; verify adopted NEC rules, product listings, manufacturer instructions, equipment markings, utility requirements, and AHJ requirements before final installation.

How to use this chart

1Start with product markingRecord the insulation type exactly as marked on the conductor or cable before choosing the calculator input.
2Tie rating to locationDocument whether the conductor is used in a dry, damp, wet, raceway, tray, burial, or service condition and verify the product rating.
3Connect to ampacity resultCarry the insulation rating into ampacity, derating, and terminal-limit review instead of treating it as a standalone approval.
Worksheet checklist. Record source basis, review gaps, and assumptions before using the chart result.
  • Record label dataWrite insulation marking, conductor material, conductor size, voltage rating if needed, and product reference.
  • Record calculator basisDocument selected insulation rating, ambient basis, conductor count, terminal rating, and calculator output.
  • Record product checksAdd manufacturer, listing, location suitability, equipment marking, and AHJ review notes before finalizing the conductor choice.
Common mistakes to avoid. Review these before turning chart current into an equipment decision.
  • Choosing the highest insulation temperature rating in the calculator without checking terminal limits and location suitability.
  • Assuming a cable or conductor is suitable for wet, burial, or service use without checking the actual product marking and instructions.
  • Treating individual-conductor insulation assumptions as valid for a cable assembly that has its own installation instructions.

Frequently asked questions

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

Is insulation type the same as final ampacity?
No. Insulation type helps select a temperature basis, but final ampacity still depends on derating, terminals, equipment, and installation conditions.
Why document wet or dry location?
A conductor can have different suitability depending on product marking and wiring method, so the calculator input must match the actual location.
Can a cable marking replace manufacturer instructions?
No. The marking identifies the product type, but installation instructions, equipment limitations, and AHJ review still matter.

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