CL2/CL3 Cable is designed for a Class 2 or Class 3 circuit, as defined by the NEC Article 725. CL2/CL3 cables are typically used for low-voltage applications such as speakers, audio/video signals, or computer data. The CL2/CL3 cables specification is designed to provide protection from both fire and electric shock. CL2 circuits are limited to up to 100VA of power at 30V, and up to 0.5VA between 30V and 150V. CL3 circuits can provide up to 100VA of power up to 150V. In most instances CL3 cables can be installed in CL2 circuits, but CL2 cables cannot be used for CL3 circuits.
CM/CMG Communications cable is designed for general use in buildings in accordance with the NEC Articale 800.53(E)(1). CM/CMG cables do not spread flame to the top of a tray in the Vertical-Tray Flame Test described in the UL 1865 standard. As a rule of thumb, CM & CMG cables are intended for installation in cable trays and other non-plenum/non-riser areas.
“Plenum” cables are constructed with a jacket made of materials that give off low amounts of smoke and which retard the spread of flames. “Plenum” is the airspace used for air circulation by an HVAC system, for example a raised floor or a drop ceiling. A popular jacket material is for CMP cables is FEP (fluorinated ethylenepropylene). CMP cables are typically manufactured with PVC components even though they are identified as separate from “PVC cables”.
CMP is a classification of cables defined by the NEC for cables intended to be installed in a building’s plenum airspaces. The most common test for CMP cables is defined by the NFPA 262 standard, which outlines criteria for both low-smoke and flame-travel performance.
CMR Cable is designated for use in riser applications. In commercial buildings, a riser is the space between floors which is used by vertical telecommunications infrastructure, connecting from one floor to another. CMR cables are intended for use within buildings in vertical shafts in accordance with Section 800.53(B) of the NEC. The test used for CMR cables is defined in the UL 1666 standard, which limits flame propagation height.
The National Electric Code (NEC) is a set of guidelines for safe installation of electrical wiring & equipment. The NEC was developed in 1897 as a way to create a national standard for electrical products & practices. The guidelines are revised every three years, most recently in 2017. Although the NEC is not the product of a governmental body, its codes and standards are often adopted by local governments to regulate safe electrical installation practices.
National Fire Protection Association (NFTA), a national non-profit organization.
Polyvinyl chloride (vinyl), is a general-purpose plastic jacket material used for cables. PVC is inexpensive and flexible. This makes it the perfect material for cable jacket for various applications including computers, communications, low-voltage wiring, etc. In the cable industry, “PVC” often indicates a cable that is not suitable for use in a plenum airspace. PVC may be dangerous in a fire situation, releasing heavy smoke and hydrogen chloride gas, which can be irritating to humans and corrosive to electronic devices. PVC cables often have a CM, CMG, or CMR rating as defined by the National Electrical Code (NEC).
Underwriters Laboratories (UL) is an independent non-profit organization that tests and certifies products for safety.