IEC 62038: Safety Requirements and Test Methods for Mains-Operated Cables, Wires and Cords

Introduction

IEC 62038 specifies safety requirements and associated test methods for mains-operated flexible cables, wires, and cords used for connecting electrical appliances and similar equipment to the supply network. Covering rated voltages up to 450/750 V, the standard addresses the full range of safety hazards: electric shock, fire propagation, mechanical damage, and thermal degradation. It applies to cords for household appliances, portable tools, temporary power distribution, and light-duty industrial equipment.

The standard defines a comprehensive suite of test methods including mechanical strength tests (tension, flexing, crushing, abrasion), heat resistance and fire propagation tests, insulation resistance and voltage withstand tests, and tests for resistance to moisture and chemicals. This article provides engineers and quality professionals with a detailed technical reference for the requirements and their practical application.

1. Mechanical Strength Requirements

1.1 Tensile Strength and Elongation

Insulation and sheath materials must meet minimum tensile strength and elongation at break values before and after thermal aging. For common PVC compounds, the standard requires tensile strength ≥ 12.5 N/mm² and elongation ≥ 150% (unaged). After aging in an air oven at 80 ± 2 °C for 7 days, retained tensile strength must be ≥ 85% and retained elongation ≥ 80%. These tests ensure the cord can withstand installation pulling forces and long-term thermal stress without cracking.

1.2 Flexing Endurance

Flexible cords are subjected to a repeated flexing test using a standard flexing apparatus. The cord is passed over a series of pulleys and a reciprocating carriage applies ≥ 10,000 flexing cycles at a specified rate. After the test, the cord must withstand a voltage withstand test at 2000 V for 5 minutes with no breakdown. This simulates the repeated bending that occurs when an appliance cord is routinely handled, wrapped, and stored.

1.3 Crush and Impact Resistance

The cord must withstand a crushing force of 1 kN applied over a 100 mm length without exposing conductors. This is particularly relevant for cords laid on floors where furniture legs or casters may apply concentrated loads. Impact resistance is verified using a spring-loaded hammer test (2 J impact energy) that simulates accidental striking of the cord.

2. Thermal and Fire Safety Requirements

2.1 Heat Resistance

Insulation and sheath materials must not deform or flow at temperatures likely to be encountered in service. The standard specifies a heat-pressure test in which a sample is subjected to a defined pressure at elevated temperature (typically 90 ± 2 °C for PVC cords) for 1 hour. The indentation depth after recovery must not exceed 50% of the original wall thickness. This prevents conductor exposure when cords are routed near heat sources or subjected to sustained high ambient temperatures.

2.2 Flame Retardance

All cords covered by IEC 62038 must pass a flame propagation test. A 600 mm vertical sample is exposed to a 175 mm high propane burner flame (1 kW nominal heat output) for 60 seconds. The charred or flaming portion must not reach within 50 mm of the upper clamp, and any flaming droplets must not ignite underlying combustible material. This requirement is critical for preventing fire propagation along cable runs in buildings.

3. Electrical Safety Tests

3.1 Insulation Resistance

The insulation resistance between conductors and between each conductor and water (after immersion) must be ≥ 0.01 MΩ·km at 70 °C when measured at 500 V DC. This test verifies that the insulation compound provides adequate ionic purity and does not contain conductive contaminants. Low insulation resistance is a strong indicator of poor compounding quality or moisture ingress during manufacturing.

3.2 Voltage Withstand (Dielectric Test)

Each completed cord must withstand a 2000 V (for 300/300 V rated cords) or 2500 V (for 450/750 V rated cords) AC test voltage applied between conductors and between all conductors collectively to water for 5 minutes without breakdown. The leakage current during the test must not exceed 2 mA per meter of cord length.

3.3 Conductor Resistance

The electrical resistance of each conductor must not exceed the values specified in IEC 60228 for the nominal cross-sectional area. For example, a 1.0 mm² annealed copper conductor must have a maximum DC resistance of 18.2 Ω/km at 20 °C. Excessive resistance indicates undersized conductors or poor-quality copper, both of which lead to overheating under load.

4. Engineering Design Insights

• Material compounding: The PVC formulation for cord insulation must balance flame retardance, flexibility, and cost. Typical formulations use 30-35% plasticizer (DINP or TOTM), 5-10% flame retardant (ATH or antimony trioxide), and 5-15% filler (chalk). Reducing filler below 10% improves fire performance but increases material cost by 15-20%.
• Conductor stranding: For maximum flex life, use fine-strand conductors per IEC 60228 Class 5 (flexible) or Class 6 (very flexible). Class 1 (solid) conductors are unsuitable for flexible cords as they work-harden and fracture after repeated bending.
• Sheath color coding: While not mandatory in IEC 62038, harmonized color coding (per IEC 60446) aids identification: brown for line, blue for neutral, green-yellow for protective earth. Cords for specific markets may require additional colors per local regulations.
• Marking durability: The surface marking (manufacturer, type, voltage rating, standard number) must remain legible after rubbing with a cloth soaked in water (15 s) and then with a cloth soaked in isopropyl alcohol (15 s). Use laser marking or high-temperature ink that bonds with the PVC matrix during extrusion.

5. Frequently Asked Questions