Which conductor type is approved for switchboard and switchgear wiring only?

The conductor type specifically approved for switchboard and switchgear wiring is TBS (Tray Cable). This type of conductor is designed to handle the demanding environments typically found in switchgear and switchboards, such as the need for robust insulation and enhanced durability against mechanical damage and electrical stress. TBS conductors have characteristics that are essential for reliable performance in high-current applications, including a wide temperature range and resistance to moisture and chemicals.

While THHN and XHHW cables are versatile and used in various applications, they are not specifically designated for switchgear and switchboard wiring. MC cable is typically used for branch circuits and has more flexible applications, but it does not meet the specific requirements for switchboard and switchgear applications like TBS does. Thus, TBS is the appropriate choice for this particular application.