Motor Lead Wire UL AWM — Selection Guide by IEC Insulation Class B, F, and H
Motor lead wire — the short conductor connecting the motor stator winding terminal to the motor terminal box — operates at the highest temperature point in the motor and must maintain insulation integrity throughout the motor’s service life. Selecting the correct UL AWM motor lead wire requires two parameters: the motor’s IEC insulation class, which determines the maximum winding temperature and therefore the minimum wire temperature rating, and the motor supply voltage, which determines whether 300V or 600V wire insulation is required.
For engineers familiar with IEC motor insulation class terminology — Class B, Class F, Class H — this guide maps each class directly to the correct UL Subject 758 AWM wire style, eliminating the specification uncertainty that arises when transitioning from IEC-standard motor lead wire to UL-recognized AWM wire for North American market equipment.
IEC Insulation Class to UL AWM Wire — Complete Mapping
| IEC Class | Max Winding Temp | Single-Phase 300V | Three-Phase 600V | Notes |
|---|---|---|---|---|
| Class A | 105°C | UL 1007 80°C / 300V | UL 1015 105°C / 600V | Rare in modern motors — most motors are Class B or above |
| Class B | 130°C | UL 3266 125°C / 300V | UL 3271 125°C / 600V | Most common class for standard industrial motors |
| Class F | 155°C | UL 3321 150°C / 600V | UL 3321 150°C / 600V | UL 3321 covers both single and three-phase at 600V |
| Class H | 180°C | UL 3135 200°C / 600V | UL 3135 200°C / 600V | 20°C thermal margin above Class H maximum |
| Class H + Braid | 180°C | UL 3071 200°C / 600V | UL 3071 200°C / 600V | With fiberglass braid — for mechanical protection in motor assembly |
Voltage Rating — Single-Phase vs Three-Phase Motor Lead Wire
The second parameter in motor lead wire selection is the motor supply voltage — which determines whether 300V or 600V insulation is required for the motor lead. The critical distinction is between nominal supply voltage and peak voltage:
- Single-phase 120V or 220V motors: Peak voltage is 120V × √2 = 170V peak, or 220V × √2 = 311V peak. Both are within the 300V rating of UL 3266 and UL 1007. Specify 300V-class wire for single-phase motors up to 220V supply.
- Three-phase 380V motors: Line-to-line peak voltage is 380V × √2 = 537V peak — exceeding the 300V rating of UL 3266. Specify 600V-class wire (UL 3271) for all three-phase 380V motor applications.
- Three-phase 480V motors: Line-to-line peak voltage is 480V × √2 = 679V peak — significantly exceeding both 300V and the nominal 480V. Specify 600V-class wire (UL 3271) for all three-phase 480V motor applications.
- VFD-driven motors: Variable frequency drives generate switching transients that produce voltage peaks above nominal bus voltage at the motor terminal. For all VFD-driven motor applications, specify 600V-class wire (UL 3271) regardless of nominal motor voltage, and consider the optional semi-conductive layer of UL 3271 for additional insulation stress protection.
UL AWM Motor Lead Wire Styles — Full Specifications
UL 3266 — XLPE 125°C / 300V — Class B Single-Phase
The compact thin-wall XLPE motor lead wire for single-phase motors up to 220V supply voltage. 32–10 AWG, 15 mils minimum average insulation wall — same physical form factor as UL 1007 PVC wire at equivalent AWG, enabling direct replacement of PVC motor lead wire with 125°C-rated XLPE without physical redesign of the motor terminal geometry. Specify for: single-phase induction motors, small appliance motors, and fractional horsepower motors where Class B insulation and 300V rating are adequate.
UL 3271 — XLPE 125°C / 600V — Class B Three-Phase
The standard three-phase motor lead wire for Class B industrial motors at 380V and 480V supply voltage. 30 AWG–2000 kcmil, scaled insulation wall from 30 mils at fine gauge to 55 mils at large conductors, rated 600V. Optional semi-conductive polymeric layer over conductor for VFD-fed motor applications. Specify for: three-phase induction motors in industrial drives, pumps, compressors, fans, and conveyor systems where Class B insulation and 600V rating are required.
UL 3321 — XLPE 150°C / 600V — Class F
The Class F motor lead wire for motors operating at higher winding temperatures — servo motors, traction motors, high-efficiency premium motors, and motors operating under sustained overload conditions where Class B wire at 125°C provides insufficient thermal margin. 30 AWG–4/0 AWG, 600V. Specify for: Class F insulation motors, high-efficiency IE3/IE4 motors where winding temperatures under full load approach or exceed 130°C, and motors in high-ambient temperature enclosures.
UL 3135 — Silicone Rubber 200°C / 600V — Class H
The Class H motor lead wire for the highest-temperature motor applications — hermetic compressor motors, high-ambient industrial motors, and specialty motors where winding terminal temperatures reach 160–180°C continuous. 26–12 AWG, 600V, extruded silicone rubber insulation. 20°C thermal margin above the 180°C Class H maximum. Specify for: Class H insulation motors, hermetic and semi-hermetic compressor motors in HVAC and refrigeration equipment, and high-ambient temperature motor applications.
UL 3071 — Silicone Rubber 200°C / 600V with Fiberglass Braid — Class H with Mechanical Protection
Style 3071 provides the same 200°C / 600V Class H thermal-electrical performance as Style 3135 with the addition of a fiberglass braid outer covering (SF-2 equivalent per UL 66) for mechanical protection during motor assembly handling. 18–13 AWG. Specify for: Class H motor lead applications where the fiberglass braid provides abrasion resistance during routing through motor end shield clearances and mechanical protection during motor assembly, maintenance, and rewinding operations.
MRO Motor Lead Replacement — Matching the Original Specification
When replacing a failed motor lead wire during motor rewinding or maintenance, the replacement wire must match or exceed the original wire’s UL Style and rating. The key information to collect from the original wire or motor nameplate:
- UL Style number — printed on the wire surface (e.g., “AWM Style 3271” or “Style 3135”)
- Temperature rating — printed on the wire surface (e.g., “125°C” or “200°C”)
- Voltage rating — printed on the wire surface (e.g., “600V”)
- AWG size — measured with a wire gauge or specified on the motor winding diagram
- Conductor type — bare copper, tinned copper, or silver-plated copper
If the original wire markings are no longer legible after thermal damage, identify the motor’s IEC insulation class from the motor nameplate and use the mapping table above to select the correct replacement UL Style. Always replace with the same or higher UL Style rating — never replace a 200°C-rated motor lead with a 125°C-rated wire.
Related UL Styles for Comparison
Motor lead wire buyers commonly cross-reference: UL 3666 (150°C / 600V silicone rubber, flexible Class F motor lead alternative to XLPE for applications requiring silicone rubber flexibility), UL 3172 (200°C / 600V silicone rubber with glass or aramid braid, 26–18 AWG Class H motor lead with enhanced braid protection), UL 1659 (250°C / 600V PTFE, for motor lead applications where chemical resistance is required alongside high temperature rating), and UL 3239 (200°C / high voltage DC, for specialized high-voltage motor and generator lead applications).
Request a Quote — Motor Lead Wire
Submit your motor IEC insulation class, supply voltage (single-phase or three-phase), AWG, conductor type, color, length requirement, and annual volume estimate below. Our technical team will confirm the correct UL Style and respond with a formal quotation within 12 business hours. Cut-to-length motor lead sets available for MRO replacement orders.
