Mineral insulated cables (BBTRZ and BTTRZ) differ by only a single letter, and both are new products without corresponding national standards. Initial users often struggle to distinguish them. So, what exactly are the differences? Let's discuss the differences.
BTTRZ Series Product Structure
Initially, my country's only mineral insulated cable was the BTTZ series copper-sheathed magnesium oxide mineral insulated cable, which meets international standards. This series of cables consists of one or more conductors in a metal sheath, tightly sealed with magnesium oxide powder mineral insulation. Because it uses Class 1 solid copper rod as the conductor, the cable is more flexible than the commonly used plastic power cables, earning it the name "rigid" mineral insulated cable.
It was precisely because of the "rigidity" of BTTZ that my country pioneered the development of copper-sheathed, corrugated mica-taped mineral-insulated cables for construction applications. Since these cables utilize the same Class 2 stranded conductors as plastic power cables, their conductors exhibit greater flexibility than BTTZ cables. To create a sales advantage, manufacturers dubbed them "flexible" mineral-insulated cables to differentiate them from "rigid" mineral-insulated cables.
The Chinese distinction makes the model names easier to understand. In Chinese cable model naming conventions, soft-core conductors are traditionally designated with the pinyin initial "R" for "soft." Therefore, BTTRZ is essentially BTTZ with the customary "R" added, representing "flexible" mineral-insulated cables.
Later, in 2011, the Ministry of Housing and Urban-Rural Development of the People's Republic of China issued the People's Republic of China Construction Industry Standard JG/T 313-2011, "Metal-sheathed Inorganic Mineral-Insulated Cables and Terminals, Rated Voltage 750V and Below" (updated to 0.6/1kV in 2014), establishing the designation for this structural product as YTTW. Somewhat embarrassingly, during the use of YTTW, people discovered that it seriously violated our traditional naming convention, and many people couldn't accept it. Where's the "R"? In China, flexible cables must have an "R" to be considered legitimate, right? Following public outcry, the National Standards Committee finally released GB/T 34926-2017, "Mica-tape mineral-insulated, corrugated copper-sheathed cables and terminations for rated voltages up to and including 0.6/1kV." This standard renamed flexible copper-core, corrugated copper-sheathed, mica-tape mineral-insulated cables to RTTZ and further optimized many details. Now, with the support of national standards, this series of mineral-insulated cables is booming. After more than a decade of market experience, we believe it will find a place in increasingly mature applications. Therefore, BTTRZ is the father of YTTW and the grandfather of RTTZ, belonging to the same family.
The Origin of BBTRZ
BBTRZ Series Product Structure
Compared to the use of copper-sheathed mineral-insulated cables, in the early days of China's construction industry, where low-smoke, halogen-free plastic cables were widely used, cost-effectiveness was paramount. The copper sheath simply incurred a significant cost premium, and early manufacturing and construction techniques were immature, often leading to cracking of the corrugated copper sheath during oxy-arc welding. Therefore, the exceptionally cost-effectiveness of fire-resistant cables using magnesium hydroxide as the insulating layer made them more accessible. They could be installed just like ordinary cables, seemingly meeting the requirements of fire-resistant electrical design, and without the risk of copper sheath cracking. As a result, widespread adoption began across China, even surpassing its cousin, BTTRZ. Every hero deserves a name. Since BTTRZ, like BTTZ, shares the noble pedigree of a copper sheath, what could be done without one? Simply change the T to B. The B stands for mineral, and it's catchy and rhymes, making it equally prestigious. Like a rising star, BBTRZ, with its prestigious name and high market recognition, has flourished.
Compared to RTTZ, BBTRZ also passes the rigorous C, W, and Z tests of BS 6387 and boasts better fire resistance than ordinary power cables. However, its actual insulation is still polyethylene plastic, and its inherent flammability doomed it to a difficult market exit. The 2014 GB 50016-2014 "Code for Fire Protection Design of Buildings" defines mineral-insulated non-combustible cables as "comprising a copper core, mineral insulation material, and a copper or other metal sheath, possessing excellent electrical conductivity, mechanical and physical properties, and fire resistance, as well as excellent non-flammability." Because BBTRZ lacks a metal sheath, it has since been phased out of the Chinese building fire protection line market.
Although BBTRZ no longer meets the requirements of the "Code for Fire Protection Design of Buildings," its cost-effective fire protection performance makes it worthwhile to continue promoting in other application areas.
The development of mineral-insulated cables in China's construction industry still has a long way to go. Flexible mineral-insulated cables have only been in use for over a decade. Whether flexible cables can truly replace rigid cables will require more time and application testing, and there's still a long way to go.
※The above description may contain contentious or inappropriate information. It is provided solely to help readers better and more easily understand the differences between the two types. We welcome your comments.
The development of mineral-insulated cables in China still has a long way to go. Flexible mineral-insulated cables have only been in use for over a decade, and there's still a long way to go. The above description may contain contentious or inappropriate information. It is provided solely to help readers better and more easily understand the differences between the two types. We welcome your comments.
