STA vs SWA Armoured Cable: Selection Guide for Underground Power Projects

STA and SWA are two common armour approaches for power cables, but the correct choice cannot be made from the three-letter abbreviation alone. The installation route, expected mechanical stress, pulling conditions, cable core configuration and project specification all affect the review. This guide explains what to confirm before requesting a quotation for an underground or industrial power cable project.

What is STA?

STA means steel tape armour. In a typical armoured power cable, overlapping steel tapes are applied over the bedding or inner sheath before the outer sheath. The armour provides radial mechanical protection against external pressure and impact. STA is commonly reviewed for multicore fixed-installation cables in underground routes, cable trenches and other locations where additional mechanical protection is specified.

This does not mean that STA is automatically suitable for every buried route. Soil conditions, duct or trench arrangement, installation method, bending, handling and the governing project specification still need to be checked. Chinese model references such as YJV22 or YJV23 indicate steel tape armoured constructions within their model system; they should be described internationally by the confirmed cable structure rather than treated as overseas certification designations.

What is SWA?

SWA means steel wire armour. Steel wires are applied around the cable bedding to provide mechanical protection and, depending on the confirmed design, can provide greater axial tensile capability than steel tape armour in suitable cable designs. SWA is typically considered where installation or pulling conditions create a defined tensile requirement, or where the project specification directly calls for steel wire armour.

SWA selection remains subject to the cable design and circuit conditions. Core configuration, conductor material, voltage class, installation method and applicable specification must be reviewed together. A supplier should not replace STA with SWA, or SWA with STA, simply because both are described as armoured cable.

STA and SWA at a glance

Five selection factors to confirm

1. Installation route

Identify whether the cable will run in a duct, trench, tunnel, tray, direct-burial route or another fixed installation. Note changes along the route, entry points and any exposed sections. The word “underground” is not enough to define the armour because underground routes can impose different handling and mechanical conditions.

2. Mechanical protection requirement

State the expected external pressure, impact or other mechanical exposure and follow the project designer’s requirement. STA is typically reviewed for radial protection, while SWA may be reviewed where the design calls for wire armour. The final choice remains subject to the complete cable construction and specification.

3. Pulling and tensile conditions

Provide the planned pulling method, route length, bends, elevation changes and any defined tensile requirement. These details help determine whether the proposed armour and overall construction are appropriate. They also affect drum length and installation planning, so they should be shared before the supplier confirms an offer.

4. Cable core configuration

Confirm single-core or multicore construction, conductor material, number of cores and cross-section. Armour selection must be reviewed together with the circuit design and applicable requirements. Do not assume that an armour arrangement used on a multicore cable can be transferred unchanged to every single-core circuit.

5. Project specification

The BOQ, cable schedule, drawings and technical specification take priority over a generic product description. Confirm voltage rating, applicable standard, insulation, bedding, armour, sheath, fire-performance requirement, tests and documents. If documents conflict, highlight the discrepancy rather than asking the supplier to guess.

Quotation and RFQ checklist

• System voltage and required cable voltage rating
• Single-core or multicore configuration
• Copper or aluminium conductor and cross-section
• Insulation, bedding and outer sheath requirement
• Required armour: STA, SWA or supplier review against the route
• Installation route, burial or duct details and pulling conditions
• Applicable standard and project specification
• Required tests, inspection and document scope
• Quantity, drum length, delivery destination and schedule