HCF-90, which features interlocked steel armor, is a derivative of Type AC Cable. It was introduced in the 1980s to support NEC Article 517 on Healthcare Facilities in "areas of patient care". This branch circuit cable is offered in 12 or 10 AWG THHN in 2, 3, or 4 conductors and was one of the original ColorSpec ID cables. The green interlocked armor became the recognized standard for healthcare facilities' cables, where redundant grounding is required. These 600V cables with THHN conductors have two paths to ground, which is a requirement of NEC 517. The outer metal jacket, in combination with a 16AWG, serves as one equipment grounding means, while the second is an additional full-size green copper ground.