Data centre and exchange cable

IS 17048:2018 Clause 10.3 rates HFFR thermoplastic at 90°C continuous conductor temperature — 20°C higher than standard PVC at 70°C per IS 694:2010. Dense data hall trays create sustained thermal stress on bundled cables; the 90°C rating permits higher current density and closer spacing without thermal de-rating becoming the size-limiting factor.

HFFR also delivers HCl < 0.5% and smoke transmittance ≥ 70% — protecting servers, storage, and networking equipment from halogen acid corrosion during fires.

Burning PVC insulation — whether FR or FR-LSH — releases hydrogen chloride gas (HCl) that corrodes electronic circuit boards, copper contacts, optical modules, and cooling systems even at sub-ignition temperatures. The damage occurs in smoke from nearby fires, not just from the cable itself burning.

HFFR per IS 17048:2018 limits HCl to < 0.5% versus < 15% for FR-LSH — a 30-fold difference. For Tier-style data hall builds, this is the difference between recoverable infrastructure after a fire and a total equipment write-off.

BT CW1308 Telephone Cable governs PABX, IDF, and admin voice distribution. Specification:

• Solid bare annealed copper conductor per IEC 60228 Class 1
• Maximum loop resistance 97.8 Ω/km
• Mutual capacitance ≤ 56 nF/km
• Working voltage 80 V (signalling level)

For LSZH variants required in halogen-free zones, the same CW1308 spec is available with HFFR sheath in place of standard PVC TM51.

The two specs serve different bandwidth tiers:

• CW1308 — voice / low-frequency PABX distribution. Bare annealed copper, designed for telephone-grade signalling.
• CW1293 (BT CW 1293 Issue 4) — high-performance data and signal cable. Tinned solid copper per ASTM B33, TI54 insulation per BS 7878. Used for low-speed data, VoIP infrastructure, and high-density signal distribution where signal integrity and crosstalk control matter.

CW1308 covers indoor PABX backbone; CW1293 covers infrastructure where pair characteristics and capacitance unbalance are tested per BT CW 1293 Issue 4.

BMS and cooling control circuits in data halls almost always require screened multicore control cable (aluminium foil + tinned drain wire) because tray density and adjacent VFDs / power feeders create high EMI exposure.

Unscreened Class 5 multicore is acceptable for digital I/O on isolated tray runs at lower density — but most data hall BMS topologies route sensor wiring through dense trays shared with cooling-pump VFDs. Specify screened with single-point screen earth per the EMC plan; the cost differential is trivial compared to commissioning rework when noise corrupts cooling control loops.