When buying a cable, you may encounter common flame-retardant ratings, such as CL2, CL3, and VW-1. These are the markings determined by UL 1581 and UL13 standards. Let's dive into the meanings behind these terms.

What Is UL? The Meaning of The UL Cable Rating 

The UL enterprise, also known by its full name Underwriter Laboratories, is a safety science company from Northbrook, Illinois approved to perform safety testing under OSHA federal agency. The company issues various equipment safety standards for equipment, including cables.

UL Standards are essential to follow as they are necessary for the safe manufacturing and maintenance of electrical wire and cable across all life stages.

UL Standards vs. NEC

While both UL Standards and the National Electric Code are important in determining the standards for electrical cables, NEC is a codified set of regularly updated laws that lists requirements for cable manufacturers. UL standards, on the other hand, are the type of certification designed to meet the standards met in NEC. 

To put it simply, an UL- certified cable follows the National Electric Code. Having your cable UL-rated means that it complies with NEC. Underwriter Laboratories influence NEC to the point that they can determine which rules will be included in NEC's new editions. However, UL does not have the power to enforce NEC; it enforces only its own standards.

Types Of Wire And Cable Safety Standards Issued By UL

• UL 13: Standard for Safety Power-Limited Circuit Cables

This standard determines the requirements for cables used in power-limited circuits.

• UL 1581: Standard for Vertical Flame Tests is basically the same as VW-1. 
• UL 62: Standard for Flexible Cords and Cables. The standard focuses on cables for flexible cords, elevator cables, and hoistway cables.
• UL 758: Standard for Appliance Wiring Materials that focuses on appliance cables used in factory equipment.

When it comes to CL2, CL3, and VW-1 markings discussed in this blog, the important standards are UL 13 and UL 1581. Other standards listed above are not related to these markings.

Note that the cables must be UL-listed to truly correspond with UL standards. If the cable is stated as UL-recognized, it simply means that the raw materials used in the creation process correspond with UL standards. This can be used as a marketing tool to sell cables of unknown quality.

CL2 vs. CL3 vs. VW-1: All About The Markings

CL2 and CL3 Marking Explained

Both CL markings correspond with UL 13 Standard for Safety Power-Limited Circuit Cables. The goal of this standard and markings is to determine whether the cables are safe for installation in buildings for general purpose applications. In practice, this means interior applications, including in-wall applications. 

The CL test is more complicated than the VW-1 test, as the cables are affected not just by the fire but smoke. Moreover, CL is a larger-quality test for cables that incorporates not just single cables but large cable trays.

CL ratings can be either riser or plenum ones. If riser, the marking's full name is CL2R or CL3R. If plenum, it is CL2P or CL3P. Riser cables are safe to install between the walls, while plenum cables are meant for air-circulated places like air ducts.

The difference between CL2 and CL3 is even more simple. CL2 are ranked 300V and above, while CL3 are low-voltage cables ranked only 150V.

VW-1 Marking Explained

VW-1 or UL 1581 is a vertical flammability test that determines the flammability of cable insulation. The test is called a Vertical Wire 1 test because, in the process of it, the cable is sustained vertically, and the source of fire is placed at one end of the cable while the piece of paper is attached to the other end. Between the two is the stretch of cotton. If the fire does not burn the piece of paper, the test is considered successfuly complete.

If the cable passes a VW-1, it is considered a flame-retardant cable safe to use in conditions that call for such cables. However, VW-1 marking does not automatically mean that the cable is safe for in-wall insulation. VW-1 cables are usually ranked 300V and higher, with XHHW-2 XLP USE-2 RHH RHW-2 copper building wire being some of the most common ones. The temperature ratings of VW-1 cables can be different, including 200°C, 250°C, 450°C

Inside VW-1 Cables

The range of cables ranked VW-1 is truly vast, as fire resistance is a must for plenty of applications across purposes and industries. Some of the cables carried by Nassau National Cable that are rated VW-1 are:

• XHHW-2 Copper Building Wire
• XLP USE-2 RHH RHW-2 Copper Building Wire
• Tray Cables with double XHHW-2 and/or RHH/RHW2 rating
• Aluminum XHHW-2 Cables
• Aluminum Photovoltaic 2Kv PV Cable
• Switchboard SIS Cables
• Welding Cables
• DLO Cable (Double-rated as RHH/RHW-2)
• High-Temperature Wire

Types Of CL2 and CL3 Rated Cables

Low-voltage flame retardant cables that are covered by CL standards, either plenum or riser, include:

• Thermostat Wire
• Alarm Wire
• Fire-Alarm Wire
• Speaker Wire