Knowledge on Cable Flame Retardancy: A Brief Introduction

Q: In the cable flame retardancy test, what are the specific scenarios for single vertical burning and bundled burning? What is the core difference between the two?

A: Single vertical burning and bundled burning are the two most commonly used methods in cable flame retardancy tests. The core difference lies in the test scenarios and the assessment focus, corresponding to different actual wiring requirements. Single vertical burning is mainly for scenarios with single or a few scattered cables, such as in homes and offices. During the test, only a single cable is vertically ignited to assess whether it can quickly extinguish itself and not drip and ignite surrounding items. For example, the power wiring on the walls of our homes needs to undergo this type of test to ensure safety.

Bundled burning, on the other hand, is for scenarios such as in subways, tunnels, high-rise buildings, and computer rooms where multiple cables are densely bundled or laid in conduits. During the test, multiple cables are bundled together and ignited. The focus is on evaluating the spread speed of the flame in the cable bundle, the heat release rate, and whether it will produce a large amount of toxic smoke. Because in these scenarios, the cables are densely arranged, once a fire breaks out, it can easily spread rapidly, causing serious accidents.

In simple terms, single burning examines the "self-extinguishing ability" of the cable, while bundled burning examines the "group fire prevention ability". The two tests complement each other, covering the cable flame retardant safety requirements in different scenarios, and are also the key basis for determining the cable's flame retardant grade. 

Q: What other aspects of the performance and safety of the cable sheath material's flame retardancy affect the usage of the cable?

A: The flame retardancy of the cable sheath material is not an independent property. Its flame retardant design is also related to multiple usage effects of the cable, such as scratch resistance, anti-aging property, and environmental friendliness, which directly affect the service life and safety of the cable. Firstly, sheath materials with good flame retardancy usually contain special flame retardants, and at the same time, they need to take into account scratch resistance. For example, in scenarios like subways and computer rooms, the cable may be subject to friction and collision, and a scratch-resistant sheath can prevent the outer skin from being damaged and the flame retardant layer from failing.

Secondly, flame-retardant sheath materials also need to meet requirements such as UV resistance and resistance to high and low temperatures. Especially for cables in outdoor or high-temperature environments, UV resistance can prevent the sheath from aging and cracking, and avoid the loss of flame retardants; the resistance to high and low temperatures can ensure that the cable maintains its flame retardant effect in extreme temperatures and does not undergo brittleness or softening.

In addition, high-quality flame-retardant sheath materials also comply with environmental standards. When burning, they do not produce a large amount of toxic and harmful smoke, reducing secondary injuries in case of a fire. Therefore, when choosing cables, one should not only consider the flame retardant grade, but also pay attention to the comprehensive performance of the sheath material to ensure that the cable can be safely and stably used in different scenarios.