Through-holes in distribution boxes are typically sized to accommodate the cross-section of busbars and incoming/outgoing cables, with dimensions varying by KVA rating and manufacturer specifications.

General Overview

Through-holes in a distribution box serve as passage points for busbars, droppers, and cables. They are usually drilled in the busbars and the enclosure to allow secure and insulated connections. The holes are often fitted with PVC insulating sleeves to prevent electrical contact and maintain safety standards .

Typical Practices

• Busbar and Dropper Holes: For 63/100 KVA boxes, busbars are typically 72×50×8 mm, and droppers are 50×8 mm. For 160/315 KVA boxes, busbars are 120×50×15 mm, and droppers are 50×15 mm. The through-holes are drilled to match the bolt size used for connections, often ranging from 8 mm to 15 mm in diameter, depending on the cross-section of the conductor .
• Cable Entry Holes: Enclosure holes for incoming and outgoing cables are generally sized to allow the cable diameter plus insulation and any protective grommets. For medium-voltage distribution boxes, these holes are often 20–40 mm in diameter, but exact sizes depend on the cable type and manufacturer .
• Insulation and Safety: All through-holes are typically lined with insulating sleeves to prevent short circuits and maintain phase separation. The sleeves are color-coded according to phase (R, Y, B) .

Recommendations

For precise installation or manufacturing, it is essential to refer to the detailed General Arrangement Drawings (GAD) provided by the manufacturer, as the exact through-hole dimensions can vary based on the box rating, cable type, and local electrical standards . If unavailable, contacting the manufacturer directly is recommended to ensure compliance with safety and operational requirements.