35 square millimeter cable connected to distribution box

A 35 mm² copper cable can safely carry approximately 125–150 A in typical three-phase distribution setups, depending on installation conditions and derating factors.Current-Carrying Capacity

The current-carrying capacity (ampacity) of a 35 mm² copper conductor depends on whether it is single-core or multi-core, the type of insulation, installation method, and ambient temperature. For example, in a standard three-phase installation with PVC insulation at 30°C ambient temperature, a 35 mm² copper cable can typically carry around 125–150 A without exceeding safe temperature limits . Aluminum conductors of the same size carry less current due to higher resistivity.

Voltage Drop Considerations

When connecting a 35 mm² cable to a distribution box, voltage drop must be considered, especially for long cable runs. Excessive voltage drop can reduce efficiency and affect sensitive equipment. Industry standards generally recommend a maximum voltage drop of 3% for branch circuits and 5% for the total system . Using a cable size calculator can help verify that the selected 35 mm² cable meets both ampacity and voltage drop requirements.

Installation Factors

Several factors influence the effective ampacity of the cable:

• Ambient temperature: Higher temperatures reduce current-carrying capacity. For example, at 40°C, the ampacity may drop by 10–15% .
• Grouping of cables: Multiple cables in a conduit or tray require derating. For instance, three or more cables together may reduce ampacity by 20–30% .
• Insulation type: PVC, XLPE, or other insulation types have different thermal ratings. XLPE allows higher current than PVC for the same cross-section .
• Installation method: Cables in free air can carry more current than those in conduits or buried underground due to better heat dissipation .

Practical Recommendations

• Ensure the cable is rated for the expected load and any future expansion.
• Use proper terminals and lugs compatible with 35 mm² conductors to connect to the distribution box.
• Verify compliance with local electrical codes (IEC 60364, NEC, BS 7671) for safety and legal requirements .
• Consider mechanical protection if the cable is exposed or runs through areas prone to damage; armored cables may be required. In summary, a 35 mm² copper cable is suitable for medium to high-current distribution circuits, but careful attention to installation conditions, derating factors, and voltage drop is essential to ensure safe and efficient operation.