PVC Sheathed Mineral Insulated Cable

950°C / 180 Minutes Circuit Integrity

Full Class A fire-resistance per GB/T 19216 and IEC 60331 — the cable maintains rated voltage and current at 950°C flame exposure for at least 3 hours. MgO has a melting point of 2,852°C; the limiting factor is the copper sheath (1,085°C melt). For the cable’s rated duration the entire current-carrying construction stays intact.

Continuous 250°C Operation, Briefly to 1,000°C

Unique among power cables, BTTVZ can run continuously at 250°C copper-sheath temperature without de-rating its dielectric strength. For brief overload or fire exposure, the copper can reach 1,000°C without losing its electrical function. This makes MI cable the only viable choice for circuits inside steel mills, glass furnaces, and similar high-temperature process plants.

Inorganic, Non-Toxic, Non-Combustible

MgO insulation, copper conductor, copper sheath — the entire current-carrying construction is non-combustible. No smoke, no halogen acid gas, no toxic emissions from the cable core when exposed to fire. The PVC outer sheath does burn during fire (the WD-BTTYZ LSZH variant addresses this), but it’s a small fraction of the cable mass and outside the electrical envelope.

Copper Sheath Doubles as Integral PE Conductor

The seamless copper tube provides a continuous metallic earth path with much larger cross-section than a typical separate PE conductor would have. This is a meaningful project-cost saving: you specify a single-core MI cable for phase, the copper sheath serves as PE, no separate earth core required. Continuous metallic shield also provides excellent EMI/lightning protection for sensitive load equipment.

Smallest OD in Its Performance Class

Compressed MgO is roughly 60 to 70 percent the volume of equivalent organic insulation at the same dielectric rating. The result: BTTVZ has the smallest OD of any cable construction with the same conductor cross-section and voltage class. Useful for retrofit projects routing through existing conduit, and for high-density cable tray installations.

100-Year Track Record, Universally Code-Accepted

Every national fire-safety code that mentions fire-survival cable accepts MI cable. BS 6207, IEC 60702, GB/T 13033, NFPA 70 (Article 332), CSA C22.2 No.124 — the standards are old, well-established, and harmonised. Project fire-safety auditors recognise BTTVZ immediately. Specifying it eliminates the certification debate that newer flexible products sometimes face on conservative projects.

MI cable termination requires specific training and specific tools (stripping tools, sealing-pot crimps, moisture-resin kits). A general electrician who hasn’t worked with MI cable will struggle and is likely to ruin cable lengths through bad terminations. Either use a contractor with MI cable experience, or budget for a one-day training session before installation starts.

The cut MgO end will absorb enough moisture to fail the insulation-resistance test within about 30 minutes in normal indoor humidity. Plan the work so cuts happen immediately before terminations are made up, or seal cut ends with heat-shrink caps if work has to pause. Megger-test before energizing — a dropped insulation reading is the visible symptom of moisture ingress.

MI cable bends, but only at controlled radii: minimum 6 times OD for cables under 9 mm OD, 8 times OD for 9-15 mm, and 10 times OD for larger sizes (BS 6207-1 table 9). Use a bending tool for accurate radii on larger cables — sharp kinks crack the MgO insulation internally and the damage is invisible until megger testing. Allow extra cable at each termination so you can re-bend if needed.

The cable’s 950°C / 180-minute fire rating only delivers if the supports holding it up survive too. Use galvanized steel clips, stainless saddles, or steel-strap supports — never plastic clips or nylon ties, which fail at 150°C. Support intervals: 600 mm for horizontal runs, 800 mm for vertical, closer at terminations and direction changes (BS 6207 Annex C).

Copper expands roughly 1.7 mm per metre per 100°C temperature rise. A 50 m run going from 20°C cold to 100°C operating temperature will grow by about 70 mm. Build expansion loops at the ends of long runs, especially between substation enclosures and equipment terminations. Failing to do this transfers thermal stress into the terminations and eventually fractures the seals.

Standard practice for MI cable: megger-test (500V or 1000V, 1 minute) before stripping, immediately after stripping but before sealing, after sealing, and after final connection. Drops in insulation resistance indicate moisture in the MgO — catch it early before the cable is buried inside a finished wall. Maintain the test records as part of the project handover; the local fire authority typically wants them.