What type of conductor is typically used for building service entrances?

Building service entrances require conductors that can handle higher currents and provide reliable performance in potentially harsh environments. THHN and THWN conductors are specifically designed for this purpose.

THHN stands for Thermoplastic High Heat-resistant Nylon-coated wire, and it is recognized for its ability to withstand high temperatures. THWN, which stands for Thermoplastic Heat and Water-resistant Nylon-coated wire, also has water-resistant properties, making it suitable for environments where moisture might be a concern.

These conductors are typically rated for higher voltages and can be used in both wet and dry locations, making them ideal for service entrance applications where safety and efficiency are paramount. They also have excellent mechanical and abrasion resistance, further enhancing their suitability for outdoor use and in areas subject to physical stress.

In contrast, other types of wires, such as NM cable or Romex, are not rated for outdoor use and typically cannot handle the same level of current or harsh conditions as THHN and THWN conductors. Flexible conduit, while useful in some applications, does not inherently provide the same electrical conductivity characteristics as these rated conductors. Therefore, using THHN or THWN conductors is the best choice for building service entrances to ensure safety, compliance, and performance.