Building cable

For general indoor power distribution at low voltage, the most common building cable worldwide is the 0.6/1kV XLPE or PVC insulated multi-core cable, typically non-armoured for conduit and tray installation or steel wire armoured (SWA) for direct burial and exposed runs. In North America, THHN/THWN-2 single conductors pulled through conduit dominate commercial and residential fixed wiring. For residential fixed wiring in many Commonwealth markets, flat twin-and-earth cable (such as 6242Y or TPS) is the standard choice for socket and lighting circuits.

Generally speaking, no, standard URD (Underground Residential Distribution) cable cannot enter a building. URD is engineered strictly for outdoor utility and underground direct burial applications. Its polyethylene jacket possesses zero flame-retardant properties. If a fire reaches it inside a structure, it will propagate flames rapidly and emit highly toxic smoke, which violates interior building codes like the National Electrical Code (NEC).

To bring power indoors, the URD cable must terminate at an exterior meter main or disconnect box and transition to an approved interior wiring method (such as THHN or XHHW-2 inside a conduit, or SER cable).

The Exception: URD cable can only enter a building if it carries a dual rating printed explicitly on the jacket, such as URD/RHW-2 or URD/XHHW-2. The secondary designation proves it has passed rigorous indoor fire-safety testing.

There is no fixed price per square foot because cabling cost depends on building type, system voltage, cable type, copper versus aluminium, length of runs, and labour rates in the region. As a rough order of magnitude for budget planning, electrical rough-in materials including cables often fall between 2and6 per square foot for standard commercial projects, with the cable itself representing a portion of that. Medium voltage feeder cables, LSZH requirements, and complex distribution designs push the number higher. For a firm estimate, provide your project’s single-line diagram and cable schedule to a supplier — they can quote the exact material cost quickly.

A 15,000 sq ft commercial building might require anywhere from 3,000 to 8,000 linear feet of main distribution and branch circuit cable, depending on the layout, ceiling height, and density of power outlets and lighting. Add separate runs for HVAC equipment, fire alarm, data, and any specialty systems. It is not a single cable figure — it is the sum of many circuits. A reliable way to estimate is to complete the electrical design and measure the actual circuit lengths on the plan, then add an allowance for drops, pulls, and waste (commonly 5–10%).

Start by identifying the mandatory standards for the project region and building type: IEC 60502, AS/NZS 5000.1, BS 7671, or NEC/NFPA 70 for North America. Then, specify only cables that carry clear markings and third-party certification to those standards. During installation, insist on verification of cable types against the approved submittals, and document the results of insulation resistance tests, continuity checks, and any required fire-performance certification. Finally, involve a qualified electrical inspector at key stages so that non-compliance is caught before walls and ceilings close.

In North American practice, “plenum-rated” mostly applies to low-voltage communication cables (CMP, CL3P) installed in air-handling spaces where smoke and flame spread must be strictly limited. The same principle applies to power cables: in buildings with open plenum ceilings or air ducts, cables need to meet flame and smoke requirements that prevent them from becoming a fire pathway. In power cabling, this typically means specifying LSZH (low smoke zero halogen) or fire-resistant cables tested to IEC 60332-3, IEC 60331, or UL classifications that limit smoke density and toxic emissions, protecting both occupants and equipment during a fire.

Inside a building, the cabling depends on the voltage and circuit. For branch circuits and lighting, single-core building wires (THHN, H07V‑K) pulled in conduit, or flat twin‑and‑earth cables (6242Y, TPS), are standard. For power distribution between panels, multi-core PVC or XLPE insulated cables — unarmoured in trays and conduit, armoured for risers or underground — cover 0.6/1kV needs. In public buildings, LSZH insulated and sheathed cables are widely used. Medium voltage cables, such as N2XSY or RHZ1, feed the building from the utility side. The common thread is that all these cables are intended for permanent, fixed installation, not for repeated flexing on a jobsite.

Start with the electrical design and the local wiring code. For a new building, the best approach is to break the building into systems — main feeders, sub-distribution, branch circuits, fire‑safety circuits, and specialty equipment — and match the cable construction to each. Use XLPE insulated, armoured cables for main feeders that will be buried or run through risers. For general indoor branch wiring, select THHN, H07V‑K, or flat twin‑and‑earth depending on the region. In any public assembly or high‑occupancy space, specify LSZH sheathed cables from the start. And confirm every cable carries the standard mark the inspector expects to see (IEC, AS/NZS, BS, or UL). When in doubt, work with a supplier who can cross‑reference your specification to exact cable types and who can deliver the full package in one shipment.