Chapter 3: Assessment of General Characteristics

BS 7671 requires a thorough assessment of electrical installations before design and implementation. This chapter ensures that installations are suitable for their intended purpose and environment.

Overview of Chapter 3 – Key Considerations

3.1 Purpose, Supplies, and Structure

• Defines the **purpose** of the installation (e.g., residential, commercial, industrial).
• Determines the **incoming supply type** (TN-S, TN-C-S, TT systems).
• Considers the **structure and layout** of circuits within the installation.

3.2 Classification of External Influences

• Evaluates **environmental conditions** that may affect electrical safety.
• Considers factors such as **temperature, humidity, mechanical stress, and chemical exposure**.

3.3 Compatibility

• Ensures that **electrical equipment** does not interfere with other components.
• Prevents **harmful interactions** between different parts of the installation.

3.4 Maintainability

• Considers the **expected lifespan** of the installation.
• Ensures that **protective measures remain effective** over time.
• Allows for **safe and efficient maintenance** procedures.

3.5 Safety Services

• Identifies **safety-critical systems** such as fire alarms and emergency lighting.
• Ensures that these systems remain **operational during faults or power failures**.

3.6 Continuity of Service

• Determines **essential circuits** that must remain operational (e.g., life support systems).
• Ensures **redundancy and backup solutions** for critical installations.

Why Chapter 3 Matters

• Ensures **electrical installations are designed for their intended environment**.
• Prevents **hazards caused by external influences**.
• Guarantees **long-term safety and maintainability** of electrical systems.