Knowledge base
Common UL flammability cable ratings
AWM (Appliance Wiring Material)
This type of wire is defined by UL 758, and is meant to be used with consumer products in basic connectivity applications, such as connecting a computer to a monitor, or routing a USB cable from a motherboard to the outside of the computer case. AWM wire is not meant to be used in building installations, unless it is within the scope of the installation instructions for a particular product (5). However, there is some overlap in test scenarios between UL 758 and UL 13 (which covers CL2, CL2X, and CL3).
VW-1 (Vertical Wire 1) - ANSI / UL 1581
The VW-1 (Vertical Wire Flame Test) is a flammability test used to evaluate the fire resistance of electrical wires and cables. The test determines whether a material can withstand exposure to a small flame without spreading the fire. Here’s a brief overview of the process:
Test Setup: A wire or cable specimen is mounted vertically, and a controlled flame is applied directly to it for a specific period (usually 15 seconds, with break of 15-60s). A paper flat is attached to the top end of the wire.
Criteria: After the flame is removed, the material is observed for flame spread, burning time, and whether or not it emits burning particles. The goal is for the specimen to self-extinguish without dripping molten material that could ignite other objects such ast the paper flag.
Passing the Test: For the cable to pass, it must not exceed a certain length of flame spread and must self-extinguish within a specific time frame. No flaming particles or dripping that would ignite a cotton pad placed below the test sample are allowed.
VW-1 is one of the standard tests used to certify cables for safety in environments where fire hazards are a concern, such as in building wiring or electronics.
CL2 (Class 2) - ANSI / UL 1685
This is one type of mark that is given to cables that meet the UL 13 "Power-limited Circuit" standard, which is designed to test the safety of cables when they are installed in buildings. CL2 uses a different test methodology than VW-1 that includes both burning and smoke. The test scale is also larger-scale than VW-1, incorporating a tray instead of a single section of wire.
CL2X and CL3
CL2X and CL3 are both cable ratings defined by the National Electric Code (NEC) and certified by Underwriters Laboratories (UL). They indicate the intended use and maximum voltage these cables can safely carry, particularly in low-voltage applications such as home automation, audio, and video systems.
CL2X
Definition: CL2X cables are designed for low-voltage use, specifically for residential environments.
Voltage Rating: These cables can carry up to 150 volts.
Usage: They are intended for use within dwellings, such as inside walls or ceilings, and are part of the "dwelling" classification. CL2X cables have less stringent flame-resistance requirements compared to their CL2 counterparts and are typically used in areas where building codes allow less demanding flame testing.
Restrictions: CL2X cables are limited to residential installations and cannot be used in the same wide range of locations as general-purpose CL2 cables.
CL3
Definition: CL3 cables are designed for general-purpose low-voltage applications.
Voltage Rating: They can carry up to 300 volts, making them suitable for more demanding installations than CL2 or CL2X cables.
Usage: These cables are often used in commercial and residential settings, including inside walls and conduits. CL3 cables are more robust, with higher fire-resistance standards, and can be used for systems that require higher power transmission, such as security systems, intercoms, and alarm systems.
Flexibility: A CL3 cable can be used in any location where a CL2 or CL2X cable is allowed, providing more flexibility for installations across various environments.
In summary, CL2X cables are more limited to residential, low-power applications, whereas CL3 cables are more versatile, with higher voltage ratings and stricter fire safety requirements for both commercial and residential installations.
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