What is a “Plenum Rated” cable?

A “Plenum” is compartment or chamber used for HVAC air distribution. In the data center, this is typically the space below a raised floor. A “Plenum Rated” cable refers to structured cabling permitted by building code for use in plenum spaces. Plenum rated cable has a slow-burning, fire-resistant casing that emits little smoke. Article 645 of the National Electric Code (NEC), titled Information Technology Equipment, discusses the use of power cables under a raised floor.