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RHH stands for Rubber-insulated, Heat-resistant, for use in Dry Locations, while RHW-2 stands for Rubber-insulated, Heat- and Water-resistant, with the “-2” indicating a 90 °C temperature rating in both wet and dry environments. The designation RHH/RHW-2 means a conductor meets the requirements for both categories, giving electrical contractors the flexibility to install one wire across a wide range of environments.
Defining the Acronyms
RHH conductors are designed for dry locations only, where they operate at temperatures up to 90 °C and withstand abrasion and heat without degrading. RHW-2, by contrast, is suitable for both wet and dry conditions, making it a versatile choice for damp industrial settings, outdoor conduit runs, and underground conduit installations where moisture is present. It is important to note that RHW-2 does not automatically carry a direct burial rating—this requires the additional USE-2 designation.
Both designations share the same construction foundation: a copper or aluminum conductor insulated with a thermoset compound such as cross-linked polyethylene (XLPE). Unlike thermoplastic insulations, XLPE retains its structural integrity when exposed to heat, giving RHH/RHW-2 excellent resistance to temperature cycling, sunlight, moisture, and many industrial chemicals.
Where RHH/RHW-2 Is Used
Because it carries a dual rating, RHH/RHW-2 is one of the more versatile thermoset building wires recognized by the National Electrical Code (NEC). It is widely used in conduit and raceways for residential, commercial, and industrial systems. In these environments, it serves as service entrance conductors, feeders, and branch circuits where protection against both heat and moisture is needed.
Construction and Compliance
RHH/RHW-2 conductors are built to comply with NEC Article 310 and UL 44 standards for thermoset-insulated wires. They typically feature solid or stranded copper or aluminum conductors. Copper is more common for feeders and branch circuits due to its conductivity and mechanical reliability, while aluminum is often chosen for larger service conductors for cost savings. The insulation is flame-retardant XLPE, which not only withstands high operating temperatures but also maintains dimensional stability under stress, helping prevent insulation creep at terminations. Products may also carry a “Sunlight Resistant” marking, which confirms compliance for rooftop and other outdoor exposed installations. These conductors are generally rated for 600 volts, though some USE-2 variations are available with voltage ratings up to 2,000 volts for utility applications.
Advantages and Limitations
RHH/RHW-2’s dual rating allows it to serve across both dry and wet environments, but there are important limitations to consider. It must be installed in conduit or raceways for mechanical protection, and it is not suitable for direct burial unless it also carries a USE-2 rating. Its ampacity can also be slightly lower than comparable conductors with thinner insulation, which should be taken into account during system design.
Key Characteristics and Ratings
What sets RHH/RHW-2 apart is its thermoset XLPE insulation. Unlike thermoplastic compounds, XLPE will not soften when exposed to heat, which gives the wire long-term stability in demanding environments. This insulation provides reliable flame resistance, withstands exposure to sunlight and moisture, and resists deformation under mechanical stress. Paired with its dual 90 °C wet and dry rating, these properties make RHH/RHW-2 a durable and dependable choice across building and industrial applications.
Quick Reference – RHH, RHW, RHW-2, USE-2, XHHW-2
| Cable Type | Full Name | Temperature Rating | Location Suitability | Direct Burial Rated | Typical Uses |
|---|---|---|---|---|---|
| RHH | Rubber-insulated, Heat-resistant, for Dry Locations | 90 °C Dry | Dry locations only | No | Indoor conduit and raceways in high-heat areas |
| RHW | Rubber-insulated, Heat- and Water-resistant | 75 °C Wet / 90 °C Dry | Wet or dry locations | No | Conduit/raceways in wet or dry environments |
| RHW-2 | Rubber-insulated, Heat- and Water-resistant (90 °C Wet/Dry) | 90 °C Wet / 90 °C Dry | Wet or dry locations | No | Versatile indoor/outdoor wiring in wet or dry locations |
| USE-2 | Underground Service Entrance (90 °C Wet/Dry) | 90 °C Wet / 90 °C Dry | Wet, dry, direct burial | Yes | Underground feeders, direct burial without conduit |
| XHHW-2 | Cross-linked polyethylene, High-Heat-resistant, Water-resistant | 90 °C Wet / 90 °C Dry | Wet or dry locations | No | Conduit and raceways where higher ampacity and thinner insulation are beneficial |
Conclusion
RHH/RHW-2 remains a dependable choice for modern building wiring where both heat and moisture protection are required. Its thermoset XLPE insulation provides durability in demanding environments, while NEC and UL recognition ensure compliance across residential, commercial, and industrial projects. By combining versatility with long-term performance, RHH/RHW-2 continues to serve as a standard solution for contractors and engineers who need reliability in a wide range of installations.
