Cable Construction

Building Wires (THHN/THWN)

Single Conductors

Individual insulated conductors for conduit and raceway installations. Most common in commercial and industrial wiring. Color-coded for phase identification. NEC Article 310.

Insulation

PVC/Nylon

Cable Types

6 types

Cable Type Specifications

NEC Article 310

Code	Full Name	Temp Rating	Location	Voltage	Notes
THHN	Thermoplastic High Heat-resistant Nylon-coated	90 °C	Dry	600V	Most common building wire
THWN	Thermoplastic Heat/Water-resistant Nylon	75 °C	Wet/Dry	600V	Wet location rated
THWN-2	THWN upgraded rating	90 °C	Wet/Dry	600V	Modern standard, replaces THWN
XHHW	Cross-linked Polyethylene High Heat/Water	90 °C	Wet/Dry	600V	XLPE insulation, better heat
XHHW-2	XHHW upgraded	90 °C	Wet/Dry	600V	90 °C wet or dry
USE-2	Underground Service Entrance	90 °C	Underground	600V	Direct burial, sunlight resistant

Selection Guidelines

• THHN vs THWN-2: THWN-2 is wet location rated at 90 °C; preferred for modern installations
• XHHW: XLPE insulation provides better heat resistance and thinner walls
• Ampacity: Use 75 °C column for terminations unless marked 90 °C (NEC 110.14)
• Colors: Black/Red/Blue (hot), White (neutral), Green/Bare (ground)

Cable Construction

Armored Cables

Metal Sheathed

Cables with metallic armor for physical protection. Used in industrial, commercial, and exposed residential applications. Provides equipment grounding path in some configurations.

Insulation

XLPE/PVC

Cable Types

5 types

Cable Type Specifications

NEC Article 310

Code	Full Name	Temp Rating	Location	Voltage	Notes
AC	Armored Cable (BX)	90 °C	Dry	600V	Flexible steel armor, bonding strip
MC	Metal Clad Cable	90 °C	Wet/Dry	600V	Interlocked metal tape or wire
MCI-A	MC Cable - Interlocked Aluminum	90 °C	Wet/Dry	600V	Aluminum armor, lighter weight
TC	Tray Cable	90 °C	Cable Tray	600V	Industrial cable trays only
PLTC	Power-Limited Tray Cable	60 °C	Cable Tray	300V	Low voltage control circuits

Selection Guidelines

• AC (BX): Bonding strip required for grounding; older residential construction
• MC: Modern replacement for AC; includes equipment grounding conductor
• Wet locations: Must be marked for wet location use; standard MC is dry only
• Support: Every 6 ft and within 12 inches of boxes (NEC 330.30)

Cable Construction

Underground & Direct Burial

Burial Rated

Cables designed for direct earth contact without conduit. Moisture and corrosion resistant. Used for service entrance, feeders to outbuildings, and landscape lighting.

Insulation

XLPE/PVC

Cable Types

4 types

Cable Type Specifications

NEC Article 310

Code	Full Name	Temp Rating	Location	Voltage	Notes
UF-B	Underground Feeder (with ground)	60 °C	Underground	600V	Residential underground, sunlight resistant
USE-2	Underground Service Entrance	90 °C	Underground	600V	Service entrance to building
URD	Underground Rural Distribution	90 °C	Underground	600V-35kV	Utility distribution, triplex/quadplex
MV-90	Medium Voltage 90 °C	90 °C	Underground	2.4kV-35kV	Utility and industrial distribution

Selection Guidelines

• UF-B: Integrated ground wire; sunlight resistant for exposed sections
• Cover depth: 24" for UF, 18" for RMC/PVC with GFCI (NEC 300.5)
• USE-2: Service entrance only; cannot be used inside building (except short transition)
• Warning tape: Install 6" above underground cables for future excavation awareness

Cable Construction

International Standards (IEC)

European/IEC Cables

Cable designations per IEC 60502 and harmonized European standards. Common in international projects and equipment. Different coding system from NEC.

Insulation

PVC/XLPE

Cable Types

6 types

Cable Type Specifications

IEC 60502

Code	Full Name	Temp Rating	Location	Voltage	Notes
NYM-J	PVC insulated, PVC sheathed (with ground)	70 °C	Dry	450/750V	European building cable
NYM-O	PVC insulated, PVC sheathed (no ground)	70 °C	Dry	450/750V	Without protective conductor
NYA	PVC insulated single core	70 °C	Dry	450/750V	Single conductor, conduit use
NYY	PVC insulated, PVC sheathed power cable	70 °C	Wet/Dry	0.6/1kV	Underground or indoor
N2XH	XLPE insulated, PVC sheathed, low smoke	90 °C	Indoor	0.6/1kV	Halogen-free, fire resistant
H07RN-F	Rubber flexible cable	60 °C	Industrial	450/750V	Flexible, oil resistant

Selection Guidelines

• NYM-J: "J" indicates protective conductor (ground); "O" without ground
• NYY: Heavy-duty power cable; can be direct buried or in conduit
• N2XH: Low smoke zero halogen (LSZH); required in public buildings
• Voltage: U0/U notation (e.g., 450/750V) = phase-neutral/phase-phase