For manufacturers exporting to the United States and buyers specifying North American cable

In North America, UL (Underwriters Laboratories) is the most recognised NRTL (Nationally Recognised Testing Laboratory). Although UL is a private organisation, the National Electrical Code (NEC, NFPA 70) requires many cable types to be "listed" by an NRTL — and UL is the dominant one. Compliance is enforced on site by the Authority Having Jurisdiction (AHJ), i.e. the local electrical inspector.

Bottom line: No UL mark (or equivalent NRTL mark) generally means a cable cannot be accepted by US distributors, contractors, or inspectors — and may be detained at customs or refused by insurers.

1. "UL Certified" Has Two Meanings

MarkWhat it coversExamplesUse
UL ListedComplete product for field useTHHN, XHHW-2, SOOW, NM-BInstalled per NEC
UL RecognizedComponent inside a larger productAWM (UL 758) hook-up wireInside listed equipment only
Critical distinction: UL 758 AWM wire is "Recognized" as a component, NOT "Listed" for NEC building wiring. You cannot substitute AWM for THHN in conduit. It is internal wiring for appliances, panels and harnesses.

2. Key UL Standards for Wire & Cable

StandardTypeCoversTypical applications
UL 44Thermoset insulationXHHW, XHHW-2, RHH, RHW, RHW-2, USE-2Building/industrial power, wet & dry, conduit, up to 2000V
UL 62Flexible cords & cablesSOOW, SJOOW, SVT, SPT, SJOWPortable tools, cord sets, extension cords
UL 83Thermoplastic insulationTHHN, THWN, THWN-2Building wire in conduit/raceway
UL 758Appliance Wiring Material (AWM)UL 1007, 1015, 2464, 2570…Internal wiring of equipment & harnesses (Recognized)
UL 1277Tray cable (TC, TC-ER)Power & control in traysIndustrial trays, raceways, exposed runs
UL 13Power-limited circuitCL2, CL3, PLTCLow-voltage control & signal
UL 444CommunicationsCategory, coaxVoice/data/network
UL 4703PhotovoltaicPV WireSolar installations
UL 1581Reference test standard—Uniform test methods (VW-1 flame, etc.)

3. Common Cable Types, Decoded

  • THHN / THWN-2 (UL 83): the workhorse building wire; THWN-2 adds wet-location rating.
  • XHHW-2 (UL 44): cross-linked polyethylene, higher temperature & moisture resistance.
  • SOOW / SJOOW (UL 62): heavy-duty flexible cord, oil- and water-resistant.
  • MTW (UL 1063): machine-tool wire for industrial control.
  • AWM styles (UL 758): thousands of internal-wiring constructions, each with its own style number, voltage and temperature rating.

4. NEC Compliance

The NEC (NFPA 70) is the enforceable code; it mandates NRTL listing for cable used in defined applications — e.g. Article 310 (conductors), Article 400 (flexible cords), Article 725 (Class 2/3 & PLTC), Article 800 (communications). The AHJ confirms compliance during inspection. Key flame test referenced across standards is the VW-1 vertical flame test.

5. Verifying the UL Mark

  1. Look for the UL mark plus the applicable standard number (e.g. "UL 44") and a file number printed on the jacket.
  2. Cross-check the manufacturer and file in UL Product iQ (iq.ul.com) or the UL Certifications Directory.
  3. Confirm the construction (gauge, insulation, rating) matches the标记 on the cable.

6. How to Obtain UL

  1. Identify the correct standard(s) for your product (a cable may need several).
  2. Submit samples and construction data to UL.
  3. Pass testing (construction, electrical, flame, aging, etc.).
  4. Pass factory follow-up inspection (regular audits are required to keep the mark).
  5. Receive Listing (or Recognition for components).
Common mistakes: using UL 758 AWM as NEC building wire; assuming CE/CPR equals UL; missing the file number on the jacket; treating CL2 / CL3 / PLTC as interchangeable (plenum/riser/general-purpose suffixes are not).

FAQ — UL Cable Certification

Q: What is the difference between UL Listed and UL Recognized?

Listed = a complete product approved for field installation (e.g. THHN, SOOW). Recognized = a component (e.g. AWM under UL 758) approved for use inside a Listed product — not for standalone NEC wiring.

Q: Does UL 758 AWM meet the NEC?

Not as building wire. AWM is a Recognized component for internal equipment wiring; NEC building wiring requires Listed cable such as UL 44 / UL 83 types.

Q: What is THHN cable?

A thermoplastic-insulated building wire covered by UL 83, commonly used in conduit for lighting and power circuits; THWN-2 adds wet-location and improved temperature ratings.

Q: Is UL required by law in the US?

UL itself is private, but the NEC (adopted by states/localities) requires NRTL listing for many cables, enforced by the AHJ inspector — so in practice, yes, for most installations.

Q: How do I verify a UL mark?

Check the UL mark + standard number + file number on the jacket, then validate the manufacturer and file in UL Product iQ (iq.ul.com).

Global buyers: compare with our EU CPR guide above. Browse all UL- and CPR-capable cable manufacturers.