— A Practical Guide for Engineers, EPCs, and Plant Operators
In industrial instrumentation, the cable is the lifeline of your control system. A damaged cable means lost signals, unplanned downtime, and costly repairs. Mechanical protection is not an afterthought—it is a fundamental design decision that determines whether your instrumentation system survives installation, maintenance, and the harsh realities of the industrial environment.
This guide compares the three primary methods of cable mechanical protection—armour, braid, and conduit—and provides a practical framework for selecting the right solution for your application.
1. Armour: Heavy-Duty Protection Built Into the Cable
Armour is a metallic layer applied directly over the cable core, beneath the outer sheath. It is the most robust form of cable protection and is designed to withstand crushing, impact, tensile loads, and rodent attack.
1.1 Steel Tape Armour (STA)
Construction: Two layers of galvanised steel tape helically wound in opposite directions, with overlapping edges--1. Tape thickness typically ranges from 0.2 mm to 0.8 mm-1.
Key Properties:
Superior crush resistance—withstands up to 2500 N/100mm-1
Excellent magnetic shielding effect against low-frequency interference-8
Bending radius ≥12× cable diameter-1
Applications: Direct burial installations, tunnels with potential rockfall, industrial floors with vehicle traffic-1, and indoor applications where space is limited-45.
Cost: STA is less expensive than SWA because it is easier to manufacture-.
1.2 Steel Wire Armour (SWA)
Construction: Single layer of galvanised steel wires (Φ0.8–3.15mm) wound helically around the cable--1.
Key Properties:
Tensile strength ≥350 N/mm²—can withstand high pulling loads-1
Excellent mechanical protection for underground and heavy-duty applications-8
Bending radius ≥10× cable diameter-1
Zinc coating ≥40 g/m² (BS standard)-1
Applications: Underground systems, vertical risers (supports self-weight), aerial spans ≤50m, mining drag applications, power networks-1-8. Blue-sheathed SWA cables are most suitable for instrumentation applications-8.
Cost: SWA is more expensive than STA due to more difficult production-.
1.3 Aluminium Wire Armour (AWA)
Construction: Aluminium wires wound around the cable-50.
Key Properties:
Non-magnetic—prevents eddy current losses in AC systems-8
Lightweight compared to steel armour-45
Corrosion-resistant-50
Applications: Single-core cables in high-voltage applications where steel armour would cause eddy current heating-1-50.
Critical Note: For single-core AC cables, aluminium armour is mandatory—steel armour can cause approximately 5% power loss at 50Hz due to eddy currents-1.
1.4 Armour Selection Summary
| Armour Type | Primary Protection | Best For | Key Limitation |
|---|---|---|---|
| STA | Crush resistance | Direct burial, tunnels, indoor | Limited tensile strength |
| SWA | Tensile + crush | Underground, vertical risers, heavy-duty | Higher cost, less flexible |
| AWA | Corrosion resistance | Single-core AC cables, weight-sensitive | Lower mechanical strength than steel |
2. Braid: Flexible Protection with Shielding Benefits
A braid is an interwoven mesh of fine wires—typically galvanised steel, copper, or bronze—applied around the cable core-50.
2.1 Construction and Properties
Construction: Interwoven galvanised steel wires (Φ0.2–0.4mm) in a mesh pattern-1.
Key Properties:
Flexibility: Bending radius ≥8× cable diameter—significantly more flexible than armoured cable-1
Shielding effectiveness: ≥60 dB at 100MHz-1
Typical coverage: ≥80% of surface area-1
Smooth outer surface for easier pulling-14
2.2 Braid vs Armour: The Trade-Off
| Comparison | Braid | Armour (SWA/STA) |
|---|---|---|
| Mechanical protection | Medium (light impacts, manual digging)-14 | High to very high (heavy loads, vehicles, excavation)-14 |
| Flexibility | High-14 | Lower-14 |
| Weight / size | Lower-14 | Higher-14 |
| Cost | Lower to medium-14 | Higher-14 |
| EMI shielding | Excellent | Limited (magnetic effect only)-8 |
The key distinction: An armoured cable generally provides more protection than a braided cable, but is heavier, less flexible, and often more expensive--14. Braided cables excel in applications requiring flexibility and EMI protection-.
2.3 Applications
Mobile equipment connections-1
EMI-sensitive environments-1
Oilfield drilling cables-1
Machine tool industry-
Routes needing flexibility with moderate mechanical risk-14
3. Conduit: External Protection for the Cable Route
Conduit is a protective tube or raceway that encloses the cable, providing mechanical protection independent of the cable construction. Unlike armour and braid, conduit is not part of the cable—it is installed separately.
3.1 Types of Conduit
| Conduit Type | Characteristics | Best For |
|---|---|---|
| Rigid Metal Conduit (RMC) | Thick-walled steel, superior protection from physical damage- | Fixed environments, heavy-duty protection- |
| Electrical Metallic Tubing (EMT) | Thin-walled steel, lighter than RMC- | Indoor commercial applications |
| Flexible Metal Conduit (FMC) | Spiral construction allows bending- | Tight spaces, irregular layouts- |
| PVC Conduit | Non-metallic, corrosion-resistant- | Underground, corrosive environments |
3.2 When to Use Conduit
Choose conduit when:
Cables are routed through high-traffic or high-risk areas where they cannot be armoured
Frequent cable changes are expected—conduit allows easy replacement-
Additional mechanical and environmental protection is needed beyond what the cable itself provides
Interlocked armour cable is used, which replaces the need for conduit for mechanical protection-
EMI shielding: For sensitive electronics, braided metal or copper conduits can prevent electromagnetic interference-. Some metallic conduits feature a braided steel cover specifically for EMC protection-.
3.3 Rigid vs Flexible: The Trade-Off
| Feature | Rigid Conduit | Flexible Conduit |
|---|---|---|
| Protection | Superior | Good |
| Flexibility | None—fixed shape- | High—can bend and twist- |
| Installation | Requires fittings for bends- | Can snake through tight spaces- |
| Best use | Fixed, permanent installations- | Areas with movement or tight spaces- |
4. Side-by-Side Comparison: Armour, Braid, and Conduit
| Feature | Armour (SWA/STA) | Braid (SWB) | Conduit |
|---|---|---|---|
| Protection level | High to very high | Medium | Variable (rigid = high) |
| Part of cable? | Yes—built in | Yes—built in | No—separate installation |
| Flexibility | Low | High | Variable |
| Cost (installed) | High | Medium | Medium to high |
| EMI shielding | Magnetic only-8 | Excellent (≥60dB)-1 | Excellent (with braided conduit)- |
| Weight | Heavy | Light | Variable |
| Tensile strength | High (SWA)-1 | Moderate | None (conduit doesn't carry tension) |
| Crush resistance | Excellent (STA)-1 | Moderate | Excellent (rigid conduit) |
| Best application | Direct burial, heavy loads-14 | Flexible routes, EMI protection-14 | Fixed routes, cable changes- |
5. Selection Decision Framework
Step 1: Assess the Mechanical Risk
| Risk Level | Recommended Protection |
|---|---|
| Heavy loads, vehicles, excavation-14 | Armour (SWA or STA) |
| Light impacts, manual digging-14 | Braid or light armour |
| Fixed routes, frequent cable changes- | Conduit |
| Tight spaces, frequent bending-14 | Braid |
Step 2: Consider Installation Constraints
| Constraint | Recommendation |
|---|---|
| Need flexibility and easier pulling-14 | Braid |
| Need maximum protection for underground-14 | Armour (SWA/STA) |
| Cables subject to tensile loads-1 | Armour (SWA) |
| Space-limited installation-45 | Braid or STA |
Step 3: Consider Shielding Requirements
| Requirement | Recommendation |
|---|---|
| EMI-sensitive environment-1 | Braid (≥85% coverage)-1 |
| Low-frequency magnetic interference-8 | Armour (STA/SWA) |
| Maximum shielding | Braid + Conduit combination- |
Step 4: Consider Environmental Factors
| Factor | Recommendation |
|---|---|
| Corrosive atmosphere-1 | Galvanised SWA (BS standard preferred)-1 |
| Temperature extremes (>90°C)-1 | Aluminium armour-1 |
| Single-core AC cable-1 | AWA (aluminium armour mandatory) |
6. Common Mistakes to Avoid
| Mistake | Consequence | Prevention |
|---|---|---|
| Using STA where tensile strength is needed- | Cable fails under pulling load | Use SWA for tension applications |
| Using SWA on single-core AC cable | Eddy current heating, power loss-1 | Use AWA for single-core AC |
| Choosing braid for heavy excavation areas-14 | Cable crushed by heavy equipment | Use armour for heavy loads |
| Ignoring bending radius | Cable damage, installation failure-1 | Match protection method to available space |
| Over-specifying armour for flexible routes | Difficult installation, higher cost-14 | Use braid where flexibility is needed |
7. Why Choose Anhui Tiankang for Mechanical Protection?
Anhui Tiankang (Group) Co., Ltd. has been manufacturing industrial cables for nearly five decades. Our instrumentation cable portfolio includes all three mechanical protection methods to match your specific project requirements.
Product Offerings:
| Protection Type | Features | Typical Applications |
|---|---|---|
| SWA Armoured Cables | High tensile strength, heavy-duty protection | Direct burial, vertical risers, underground |
| STA Armoured Cables | Crush resistance, cost-effective | Tunnels, industrial floors, indoor |
| Braided Cables (SWB) | Flexible, EMI shielding, smooth surface | Mobile equipment, oilfield drilling, tight spaces |
| Conduit-Compatible Cables | Designed for conduit installation | Fixed routes, frequent cable changes |
Core Advantages:
CNAS-accredited laboratory: Full mechanical and electrical testing
Comprehensive certifications: CCC Ex, ATEX, IECEx, CCS marine
Proven track record: Long-term supplier to CNPC, Sinopec, CNOOC, and international EPC projects
Complete package: From instrumentation to cables to accessories—one-stop supply
8. Conclusion
The choice between armour, braid, and conduit is not about which is "better"—it is about which is right for your specific application.
| If you need... | Choose... |
|---|---|
| Maximum protection from heavy loads and excavation | Armour (SWA or STA) |
| Flexibility with moderate mechanical protection | Braid (SWB) |
| Fixed routes with frequent cable changes | Conduit |
| EMI protection with mechanical protection | Braid or conduit with braided cover- |
| Tensile strength for vertical or long pulls | Armour (SWA) |
| Crush resistance for buried or floor installations | Armour (STA) |
The key takeaway: Understand the mechanical risks, installation constraints, and environmental factors of your project before selecting a protection method. The right choice from the start prevents costly failures and downtime later.
Contact Us
For cable selection advice, technical documentation, or project quotations, please contact:
Yin Shuangjie
International Sales Manager
📧 Email: [email protected]
📱 WhatsApp / Zalo: +86 17856068126
🌐 Website: http://www.tiankang-global.com/
Anhui Tiankang – Your partner for reliable instrumentation cable solutions.
