What is UL 44?

What is UL 44?  

UL 44 is the standard for Thermoset-Insulated Wires and Cables. Unlike "thermoplastic" wires (like THHN) that can melt or soften under extreme heat, UL 44 wires use XLPE (Cross-linked Polyethylene) or EPR (Ethylene Propylene Rubber). These materials are chemically "locked" together to stay structurally solid even under massive thermal stress.

The Construction Essentials

• Insulation (Thermoset): Typically XLPE or EPR. These materials prevent "insulation flow," meaning the wire won't thin out or short-circuit if it gets hot in a crowded conduit.

• Conductors: Stranded or solid Copper or Aluminum.

• Voltage: Primarily rated for 600V, though some specialized variants are rated up to 2000V.

Example of UL 44 Listed XHHW-2 Copper Building Wire with an XLPE Insulation 

Cracking The Code: What the Letters Mean

The UL 44 standard uses a specific "letter code" system that dictates where the wire can be legally installed per the National Electrical Code. Below is an example for RHHW-2.

• R: Rubber (or a thermosetting equivalent like XLPE).

• HH: High Heat (Rated for 90°C in dry locations).

• W: Water Resistant (Rated for wet locations).

• -2: The "Golden Ticket" (Rated for 90°C in BOTH wet and dry locations).

Why Engineers Specify UL 44 Over UL 83 (THHN)

While THHN is common, UL 44 wires (like XHHW-2) are specified for "Mission Critical" environments for three reasons:

1. Lower Leakage Current: UL 44 insulation has superior dielectric properties, making it safer for long-distance power runs.

2. No Nylon Jacket Needed: THHN requires a thin nylon skin to protect the PVC underneath. UL 44 insulation is rugged enough to stand alone, making it easier to strip.

3. Chemical & Environmental Grit: These cables are engineered to handle the "mud," moisture, and aggressive chemicals found in industrial plants and offshore rigs.

4. Testing Standards: Cables must pass rigorous, for example, flame tests (VW-1) and, for example, cold bend tests (-25°C).
   
   Pro-Tip: Because UL 44 wires don't rely on a nylon jacket for moisture protection, they are immune to the 'Nylon Skin' issues where the outer layer of THHN can tear or degrade in high-chemical or high-moisture environments

Common Applications

• Service Entrances: Bringing power from the transformer to the building.

• Industrial Feeder Circuits: High-ampacity power in factories and data centers.

• Conduit & Raceways: General-purpose wiring in hospitals and schools where safety and thermal stability are paramount.

How Wire America Can Help

At Wire America, we specialize in professional-grade UL 44 Thermoset-Insulated cables engineered for mission-critical industrial and commercial infrastructure. Our supply is built to handle everything from standard service entrances to high-heat industrial feeders.  Because our material is often triple-rated, you get a single wire versatile enough for general building, industrial feeders, and even direct burial. 

• RHH / RHW-2 / USE-2: We offer triple-rated XLP cables that offer maximum versatility. These are the "go-to" for direct burial and wet-location applications where failure isn't an option.

• XHHW-2: Our XHHW-2 collection features high-performance XLPE insulation that is easier to pull through conduit and offers superior chemical resistance compared to standard building wire.

• DLO: Our flexible Diesel Locomotive Cable is 2000V rated cable, has an EPR insulation and listed as RHH/RHW-2 per the UL 44 standard.

Because we offer our most of our UL 44 wire by the foot, you never have to pay for excess copper or aluminum. Whether you are wiring a single sub-panel or an entire industrial facility, we provide cut-to-length solutions that are ready to ship.

Recommended for Installation

Completing a service entrance? Don't forget your Bare Copper Grounding Wire to ensure your system meets NEC grounding requirements. Proper grounding is essential for the safety and stability of UL 44-rated industrial feeders and service entrances.

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Official Standards & Technical Resources

To verify compliance for your next project, refer to these primary sources:

• Official UL Standard: UL 44 Standard for Thermoset-Insulated Wires
  

• Harmonized Standard (Canada): CSA C22.2 No. 38 (Thermoset-Insulated Wires and Cables)

• Testing Benchmark: IEEE 1202 / UL 1685 (Vertical-Tray Fire-Propagation Test)
  
  

At Wire America, we believe in genuine conversation. You'll always talk with real people who understand that every project requires careful product selection. We're here to ensure you feel educated, confident, and great about your final purchase. Feel free to give us a call to discuss your project! You can reach us at: 833-268-8644

⚠️ Important Disclaimer: Safety and Compliance

Wire America provides this information as a guide only. Electrical installations must strictly adhere to the National Electrical Code (NEC) and all state, local, and jurisdictional requirements, which vary widely. Always consult a licensed electrician, electrical engineer, or the local inspecting authority before purchasing material or starting any electrical project. Wire America assumes no liability for the installation, use, or interpretation of these guides.