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What is the UL vw-1 vertical wire flame test?

2023-11-20 13:04

The UL VW-1 Vertical Wire Flame Test is a standard fire test used primarily for assessing the fire-resistant properties of wires and cables. It's a part of the safety evaluations conducted by Underwriters Laboratories (UL), an independent safety science company. The test determines the cable's ability to resist the propagation of flame along its length when exposed to fire.

The UL VW-1 test evaluates the fire-retardant characteristics of wire and cable materials when subjected to specific conditions. Here's an overview of the test procedure:


The primary objective is to assess the performance of wires and cables when exposed to a vertical flame. The test measures the flame propagation, burning behavior, and self-extinguishing capability of the materials.

Test Setup:

  • Sample Preparation: The wire or cable sample, usually around 1.8 meters long, is prepared for testing.
  • Test Chamber: The sample is vertically mounted in a chamber where a specified flame is applied.
  • Flame Application: A controlled flame is placed at the bottom of the vertical sample. The sample's reaction to the flame is observed.

Test Procedure:

  1. Ignition: The flame is applied to the bottom end of the vertically suspended wire or cable sample.
  2. Flame Exposure: The sample is exposed to the flame for a specific duration as per the test standard.
  3. Observation: Observers monitor various aspects such as flame spread, burning rate, dripping, and any self-extinguishing behavior.
  4. Criteria Assessment: The test evaluates if the flame spreads beyond certain predefined points along the length of the sample. Criteria for passing or failing the test are based on flame propagation and extinguishing behavior.

Evaluation Criteria:

The assessment criteria involve the following aspects:

  • Flame Spread: The distance and speed of flame propagation along the sample.
  • Burning Behavior: Observations on dripping or flaming debris that could cause fire spread.
  • Self-Extinguishing: The sample's ability to stop burning after the removal of the flame source.
  • Duration of Burning: How long the sample sustains burning after flame removal.

Test Standard Compliance:

The UL VW-1 test adheres to specific standards outlined by Underwriters Laboratories, which define the criteria for passing or failing the test. Compliance with these standards ensures the safety and quality of wires and cables in various applications.


This test is crucial in determining the fire safety of wires and cables used in different industries, including electrical, automotive, aerospace, and construction. Compliance with fire safety standards is essential to prevent fires caused by wires or cables in both residential and industrial settings.


The UL VW-1 Vertical Wire Flame Test is a vital assessment method that ensures wires and cables possess adequate fire-resistant properties, limiting flame spread and promoting self-extinguishing behavior when exposed to fire. This test contributes significantly to enhancing fire safety standards across various industries.

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