In-Depth Technical Study on Low Voltage (LV) Power Cables: Design, Ratings, Ampacity & Selection Criteria

1.0 📚 Introduction

Low Voltage (LV) cables are electrical conductors designed for voltage ratings not exceeding 1000 V AC or 1500 V DC as per IEC and national regulations (e.g., SBC in Saudi Arabia). These cables form the backbone of electrical infrastructure in buildings and industrial environments.

The reliability, safety, and efficiency of an electrical installation depend significantly on correct LV cable selection, installation, and sizing.

---

2.0 🏷 Definition and Voltage Class (IEC 60502-1)

Per IEC 60502-1, LV cables are classified as:

Marking	Meaning
0.6/1 kV	Maximum permissible voltage is 600 V between conductor and earth, and 1000 V between conductors (U₀/U)
300/500 V	Typically for control and instrumentation, light-duty cables

---

3.0 🧱 Cable Construction in Detail

LV cable construction involves six functional layers. Their materials and properties are critical to mechanical strength, electrical safety, and thermal behavior.

3.1 Conductors (IEC 60228)

• Material: Copper (Cu) or Aluminium (Al)
• Construction Classes:
  • Class 1: Solid
  • Class 2: Stranded
  • Class 5: Flexible
• Standard cross-sections: 1.5 mm² to 630 mm² for LV applications

3.2 Insulation

• PVC (Polyvinyl Chloride):
  • Temp rating: 70°C
  • Economical, good chemical resistance
• XLPE (Cross-Linked Polyethylene):
  • Temp rating: 90°C (normal), 130°C (overload), 250°C (short-circuit)
  • Higher ampacity, better thermal and mechanical performance

3.3 Bedding (Inner Sheath)

• Extruded PVC or thermoplastic fillers
• Prevents conductor damage from armour

3.4 Armouring (optional)

• SWA (Steel Wire Armour) for mechanical protection in underground or exposed installations
• Required for cables laid in ducts, trenches, or outdoor mechanical areas

3.5 Outer Sheath

• PVC: standard
• LSZH: for low smoke, halogen-free environments (fire safety zones, data centers, tunnels)

---

4.0 ⚡ Ampacity (Current-Carrying Capacity)

Ampacity is governed by:

• Conductor size & material
• Installation method (A to G) – per IEC 60364-5-52
• Ambient temperature
• Soil thermal resistivity (if buried)
• Grouping factor – correction for multiple cables

---

4.1 IEC-Based Ampacity Table (Copper, XLPE, Ambient 30°C)

Cross Section (mm²)	In Conduit (A)	In Air (A)	Buried (A)
1.5 mm²	19 A	23 A	18 A
2.5 mm²	26 A	30 A	24 A
4 mm²	36 A	39 A	32 A
6 mm²	47 A	50 A	41 A
10 mm²	65 A	68 A	57 A
16 mm²	87 A	89 A	76 A
25 mm²	114 A	119 A	99 A
35 mm²	141 A	144 A	122 A
50 mm²	176 A	180 A	150 A

🔎 Apply correction factors for:

• Ambient >30°C (e.g., 0.94 for 40°C)
• Grouping (e.g., 0.85 for 2 cables, 0.75 for 3+ cables)
• Soil resistivity >1.5 K·m/W (for buried cables)

---

5.0 ⚙ Cable Markings (IEC 60446)

Example:
Cu / XLPE / SWA / PVC 4C x 25 mm², 0.6/1kV

• Cu: Copper conductor
• XLPE: Cross-linked insulation
• SWA: Steel wire armour
• PVC: Outer sheath
• 4C: Four cores
• 25 mm²: Core size
• 0.6/1kV: Rated voltage

---

6.0 📏 Selection Criteria

Parameter	Consideration
Voltage Drop	Must not exceed 3% for lighting, 5% for other circuits (IEC 60364)
Short-Circuit Withstand	kA rating based on conductor size & fault duration
Installation Environment	Indoor, buried, ducted, exposed
Fire Resistance	LSZH or FRLS cables for emergency systems
Mechanical Stress	Use armoured cable for exposed/buried routes
Certification	Use SEC or SASO-approved cables in KSA

---

7.0 🌍 GCC Practices (Saudi Arabia Focus)

• SEC-approved cables follow IEC 60502-1 and SBC 501
• MV cables: Cu or Al / XLPE / SWA / PVC, typically buried
• LV indoor cables: Cu / XLPE / LSZH or PVC
• Emergency power & fire alarm: must be fire-rated, LSZH, red sheath

---

8.0 ✅ Conclusion

Low Voltage cables are complex systems with layers of mechanical, thermal, and electrical engineering. Compliance with IEC, SBC, and local utility standards is mandatory to ensure safety and durability. Selection should be based on environmental, electrical, and safety parameters — not just price or availability.

---

📎 References

1. IEC 60502-1: Power Cables with Extruded Insulation
2. IEC 60228: Conductors of Insulated Cables
3. IEC 60364-5-52: Selection and Erection of Wiring Systems
4. SBC 501: Saudi Building Code – Electrical
5. IEEE 835: Standard Power Cable Ampacity Tables