Common Questions and Answers About Building Wires Based on IEC Standards

1. What is the definition and scope of application of building wires in IEC standards?
According to IEC standards, building wires refer to insulated wires or cables used for power distribution within buildings (residential, commercial, industrial). They mainly connect distribution panels to electrical equipment (such as sockets, lighting fixtures, and appliances) and typically operate at voltages not exceeding 1000V AC or 1500V DC (corresponding to standards like IEC 60228 and IEC 60245).
Their scope of application includes:
Fixed power lines inside buildings (e.g., in walls, ceilings, cable trays);
Connection lines between equipment and power distribution systems;
Flexible cables for short-term or temporary use (e.g., cords for portable appliances).

2. What are the main types of building wires in IEC standards?
IEC classifies building wires into the following categories based on their purpose, insulation materials, and structure:
Single-core or multi-core insulated wires (IEC 60228, IEC 60245)：
Single-core wires: Used for fixed installation, with conductors made of copper or aluminum, and insulation materials mostly PVC (polyvinyl chloride), XLPE (cross-linked polyethylene), etc.
Multi-core cables: Such as flexible cables (IEC 60245), composed of multiple insulated conductors covered by a sheath. They are suitable for occasions requiring bending (e.g., connecting wires for appliances).
Sheathed cables (IEC 60502, IEC 60754)：
Multi-core cables with a sheath, where the sheath material is PVC or rubber, providing mechanical protection and moisture resistance. They are often used in damp environments (e.g., bathrooms, underground).
Fire-resistant cables (IEC 60331, IEC 61034)：
Cables with flame-retardant or fire-resistant properties, such as low smoke zero halogen (LSZH) cables, which release less smoke and low toxicity in case of fire. They are suitable for high-rise buildings, hospitals, and other places.

3. How does IEC specify the conductor materials and specifications for building wires?
Conductor materials：
Copper conductors (IEC 60228) are preferred due to their good conductivity and oxidation resistance. Aluminum conductors must meet higher mechanical strength requirements (e.g., annealing treatment) and require anti-corrosion design at connections.
Conductor specifications：
The cross-sectional area (mm²) of the conductor is the core parameter, rather than the AWG (American Wire Gauge). IEC 60228 defines the nominal cross-sectional areas of conductors (e.g., 0.5mm², 1mm², 2.5mm², 4mm², etc.) and specifies the maximum current-carrying capacity corresponding to different cross-sectional areas (adjusted according to the ambient temperature and laying method).
For example: A 2.5mm² copper conductor laid in air (ambient temperature 30°C) has a current-carrying capacity of approximately 24A (refer to IEC 60364-5-52).

4. What requirements does IEC have for insulation and sheath materials of building wires?
IEC has strict regulations on the performance of insulation and sheath materials (e.g., temperature resistance, aging resistance, flame retardancy):
Insulation materials：
PVC (IEC 60884): Usually with a temperature resistance rating of 70°C or 90°C, suitable for general environments;
XLPE (IEC 60502): Resistant to temperatures above 105°C, anti-aging, suitable for high-temperature environments;
Rubber (IEC 60245): Flexible, oil-resistant, and weather-resistant, suitable for mobile equipment.
Sheath materials：
Must have mechanical strength (tear resistance, wear resistance) and environmental adaptability (moisture resistance, UV resistance);
LSZH sheaths (IEC 61034) release hydrogen halide gas at a concentration of ≤5mg/m³ in fire, suitable for crowded places.

5. How is the current-carrying capacity of building wires determined in IEC standards?
Current-carrying capacity (the maximum current allowed to pass through for a long time) is a core parameter for wire safety, clearly specified in IEC 60364-5-52:
The current-carrying capacity must be calculated comprehensively based on the conductor cross-sectional area, insulation material temperature resistance rating, laying method (e.g., in air, buried, in a pipe), and ambient temperature (-5°C to 40°C);

6. What requirements does IEC have for the flame retardancy and fire resistance of building wires?
Flame retardancy (IEC 60332)：
Wires must pass vertical burning tests (single or bundled burning), with the flame spread distance not exceeding the specified value, and self-extinguishing within 30 seconds after the fire source is removed;
Bundled cables (e.g., multiple cables tied together) must pass the IEC 60332-3 test to ensure they do not spread rapidly in a fire.
Fire resistance (IEC 60331)：
Fire-resistant cables must maintain power supply for 1-3 hours (depending on the grade) in a flame of 750°C-950°C, suitable for critical circuits such as fire protection systems and emergency lighting.

7. Which IEC standards must be followed for the installation of building wires?
Installation must comply with the IEC 60364 (Electrical installations of buildings) series of standards:
Laying methods: Exposed laying (along walls, ceilings) must be firmly fixed; concealed laying (buried in walls, floors) must be protected by pipes to avoid mechanical damage;
Bending radius: The bending radius of single-core hard wires must not be less than 6 times the conductor diameter, and that of multi-core flexible wires must not be less than 10 times (to prevent insulation cracking);
Connections: Terminals conforming to IEC 60998 must be used to ensure low contact resistance and no loosening. For aluminum conductors, copper-aluminum transition terminals must be used to prevent electrochemical corrosion.