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1. Overview of EN 50525-3-31 

Scope: 
This standard specifies the **design, materials, construction, and testing** requirements for **single-core, non-sheathed cables** that offer enhanced safety in fire situations. 

Key Characteristics: 

• Rated Voltage: Up to and including 450/750 V (U₀/U).
• Special Fire Performance: Halogen-free, low smoke, and reduced emission of corrosive gases.
• Insulation Material: Thermoplastic compounds that are halogen-free.
• Application: Fixed installations where fire safety is critical, such as public buildings, hospitals, and transportation systems.

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2. Key Features of Cables Under EN 50525-3-31 

1. Halogen-Free Insulation: 
- Insulation material does not release halogen gases, which can be toxic and corrosive during combustion. 
- Reduces the formation of hydrochloric acid and other harmful compounds in the event of fire. 

2. Low Smoke Emission: 
- Produces minimal smoke when burning, improving visibility for safe evacuation. 
- Reduces smoke damage to equipment and facilities. 

3. Single-Core Design: 
- Consists of a single conductor with thermoplastic insulation, optimized for fixed installations.

4. Environmental Benefits: 
- Cables meet modern safety and environmental standards, contributing to sustainability. 

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3. Applications of EN 50525-3-31 Cables 

These cables are designed for environments where **fire safety and reduced toxicity** are priorities:

• Public Buildings: Schools, hospitals, libraries, and theaters.
• Transportation Infrastructure: Airports, metro systems, tunnels, and train stations.
• Industrial Facilities: Chemical plants, power stations, and data centers.
• Residential Buildings: High-rise apartments and smart homes with high safety requirements.

Example Use Case: 
In a **hospital**, EN 50525-3-31 cables are installed for powering critical systems such as lighting and medical equipment, ensuring minimal smoke and toxicity during emergencies.

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4. Construction of EN 50525-3-31 Cables 

1. Conductor: 
- Made of **copper**, typically annealed for optimal conductivity. 
- Available in solid or stranded forms depending on flexibility needs. 

2. Insulation: 
- Halogen-free thermoplastic material, such as low-smoke zero halogen (**LSZH**) compounds. 
- Designed for low toxicity and minimal environmental impact.

3. Cross-Sectional Area: 
- Available in standard sizes, typically ranging from **1 mm² to 10 mm²**, depending on current-carrying capacity requirements.

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5. Advantages of EN 50525-3-31 Cables 

1. Fire Safety: 
- Reduced flame spread minimizes fire propagation. 
- Halogen-free materials prevent the release of toxic gases during combustion.

2. Low Toxicity: 
- Safe for use in densely populated or enclosed spaces where the release of corrosive gases could endanger life or equipment.

3. Environmental Compliance: 
- Cables align with modern environmental and health safety standards, reducing harmful emissions.

4. Easy Installation: 
- Lightweight and flexible single-core design simplifies installation in fixed wiring systems.

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6. Testing Requirements for EN 50525-3-31 Cables 

Cables must undergo rigorous testing to ensure compliance with the standard: 

1. Electrical Tests: 
- Insulation resistance tests. 
- Voltage withstand tests.

2. Fire Performance Tests: 
- Flame retardancy tests to verify compliance with IEC 60332-1-2. 
- Smoke density tests (e.g., EN 61034) to ensure minimal smoke generation. 

3. Mechanical Tests: 
- Tensile strength and elongation tests for insulation materials. 

4. Halogen-Free Verification: 
- Tested according to EN 50267 to confirm the absence of halogens in the materials. 

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7. Compliance and Relevant Standards 

Cables conforming to EN 50525-3-31 must meet additional standards, such as: 

 
 

Standard	Purpose
EN 61034	Measurement of smoke density during fire tests.
EN 50267	Determination of halogen acid gas emissions during combustion.
IEC 60332-1-2	Tests on flame retardancy.
EN 50525-2-41	Cables with thermoplastic insulation for general use.

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8. Conclusion 

**EN 50525-3-31** is essential for specifying cables that prioritize **fire safety**, **low toxicity**, and **environmental protection**. These cables are ideal for fixed installations in environments requiring enhanced safety, such as public infrastructure and industrial facilities.

Key Takeaway: 
By ensuring low smoke, zero halogen emissions, and reliable performance, EN 50525-3-31 cables contribute significantly to modern safety and sustainability standards.

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