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RHW RHH insulation specifications

RHW and RHH insulation corresponds to copper or aluminum conductors with a thermoset cross-linked polyethylene (XLPE) covering, designed for AC and DC power distribution up to 600 V. The RHH designation identifies conductors suitable for dry locations with a maximum operating temperature of 90 °C / 194 °F, while RHW is specified for wet environments up to 75 °C / 167 °F. Variants with the -2 suffix, such as RHW-2, extend the capacity to 90 °C / 194 °F also under wet conditions. These conductors comply with the requirements of the National Electrical Code (NEC, NFPA 70) and are commonly used in telephone central offices, transmission stations, and telecommunications cabinets where high thermal and dielectric resistance is required.

Technical Properties

Section titled “Technical Properties”
Property Value Reference Standard
Maximum rated voltage 600 V AC/DC NEC (NFPA 70), UL 44
Maximum dry temperature (RHH) 90 °C / 194 °F NEC Table 310.4(A)
Maximum wet temperature (RHW) 75 °C / 167 °F NEC Table 310.4(A)
Maximum wet temperature (RHW-2) 90 °C / 194 °F NEC Table 310.4(A)
Insulation material Silicone-free cross-linked polyethylene (XLPE) ASTM D2655
Flame resistance VW-1 or FT-2 UL 1581
Conductor class Class B (standard) or Class I (flexible) ASTM B8 / ASTM B172
Insulation volume resistivity ≥ 10¹⁴ Ω·cm at 20 °C / 68 °F ASTM D257

Construction

Section titled “Construction”

The annealed copper conductor, solid or stranded, is manufactured under ASTM B3 (bare copper) or ASTM B33 (tinned copper) specifications. In the Class B version, individual wires are arranged in one or more concentric helical layers, while Class I uses rope-stranded members composed of small-diameter wires, typically between 24 AWG and 34 AWG. A uniform-thickness XLPE extrusion is applied over the copper to ensure dielectric integrity even in the presence of moisture, salt fog, and chemical agents typical of basements, underground vaults, and outdoor cabinets.

Dimensions and Cross-Sectional Areas

Section titled “Dimensions and Cross-Sectional Areas”

The following table relates the most commonly used AWG sizes in RHH/RHW power cables with their conductor dimensions, corresponding to solid or Class B stranded conductors.

AWG Conductor Diameter Cross-Sectional Area
14 1,63 mm / 0.0641 in 2,08 mm² / 0.00322 in²
12 2,05 mm / 0.0808 in 3,31 mm² / 0.00513 in²
10 2,59 mm / 0.102 in 5,26 mm² / 0.00815 in²
8 3,26 mm / 0.129 in 8,36 mm² / 0.0130 in²
6 4,11 mm / 0.162 in 13,3 mm² / 0.0206 in²
4 5,19 mm / 0.204 in 21,1 mm² / 0.0328 in²
2 6,54 mm / 0.258 in 33,6 mm² / 0.0521 in²
1/0 8,25 mm / 0.325 in 53,5 mm² / 0.0829 in²
2/0 9,27 mm / 0.365 in 67,4 mm² / 0.104 in²
4/0 11,7 mm / 0.460 in 107 mm² / 0.166 in²

Electrical Resistance Calculation Formula

Section titled “Electrical Resistance Calculation Formula”

R = ρ * L / A

Variable Meaning Unit
R Electrical resistance of conductor at 20 °C / 68 °F Ω
ρ Resistivity of annealed copper (0,0172 Ω·mm²/m) Ω·mm²/m
L Total length of conductor m
A Actual cross-sectional area of conductor mm²

Applications

Section titled “Applications”

RHW/RHH conductors are installed in AC and DC power supply circuits up to 600 V within central offices (CO), transmission stations, cellular tower sites, and remote outside plant cabinets. The RHH rating covers runs in dry indoor locations, cable trays, and conduits not exposed to weather. The RHW variant is used in cable vaults, partially covered basements, restricted access spaces with moderate dampness, and direct earth burial in concrete slabs. Cables with dual RHH/RHW-2 marking act as a universal solution for all three environments — dry, damp, and wet — and are selected when cable routes pass through sections with changing environmental conditions.

Frequently Asked Questions (FAQ)

Section titled “Frequently Asked Questions (FAQ)”

What is the maximum operating temperature of RHW insulation in wet environments?

Section titled “What is the maximum operating temperature of RHW insulation in wet environments?”

Standard RHW insulation supports a maximum temperature of 75 °C / 167 °F in wet environments, while the RHW-2 version reaches 90 °C / 194 °F under the same conditions.

What rated voltage do RHH/RHW conductors support?

Section titled “What rated voltage do RHH/RHW conductors support?”

The maximum rated voltage is 600 V in both AC and DC, according to NEC requirements.

What is the diameter of a 6 AWG conductor used in RHW RHH cable?

Section titled “What is the diameter of a 6 AWG conductor used in RHW RHH cable?”

A 6 AWG copper conductor has a diameter of 4,11 mm / 0.162 in and a cross-sectional area of 13,3 mm² / 0.0206 in².

What electrical resistance per unit length does a 10 AWG copper conductor offer at 20 °C?

Section titled “What electrical resistance per unit length does a 10 AWG copper conductor offer at 20 °C?”

For a 10 AWG annealed copper conductor (5,26 mm² / 0.00815 in²) the approximate resistance is 3,27 Ω per 1000 m / 1,0 Ω per 1000 ft, calculated with a resistivity of 0,0172 Ω·mm²/m.

In what environments can a cable with dual RHH/RHW rating be installed?

Section titled “In what environments can a cable with dual RHH/RHW rating be installed?”

A cable with dual RHH/RHW rating can be installed in dry locations (up to 90 °C / 194 °F), damp and wet locations (up to 75 °C / 167 °F or 90 °C / 194 °F if RHW-2), covering from telephone central office interiors to underground vaults with water presence.

What stranding class does a flexible RHW RHH cable use?

Section titled “What stranding class does a flexible RHW RHH cable use?”

Flexible cables under this specification use Class I conductor per ASTM B172, formed by rope-stranded members which in turn are composed of small-diameter wires, typically between 24 AWG and 34 AWG.

References

Section titled “References”