Secondary distribution box inlet and outlet bushings

Secondary bushings in distribution boxes provide safe, insulated connections between transformer secondary windings and external low-voltage cables.

Function and Purpose

Secondary bushings serve as insulated passageways for low-voltage conductors from the transformer's secondary winding to the external distribution system. They allow safe connection of inlet and outlet cables without exposing live parts, maintaining electrical insulation and mechanical stability inside pad-mounted or cubicle-type distribution transformers ( ).

• Inlet bushings connect incoming low-voltage power to the distribution box or transformer secondary terminals.
• Outlet bushings provide connection points for outgoing circuits to feed multiple loads safely.

Construction and Materials

Secondary bushings are typically molded from high-temperature nylon (Zytel® HTN) for mechanical strength, temperature stability, and low moisture absorption ( ). They include:

• Clamping flanges or tri-clamp designs for secure mounting.
• Gasket surfaces with Buna-N rubber to ensure tight sealing and prevent moisture ingress.
• Stud or spade connections for cable attachment, with standard sizes like 5/8" or 1" copper studs, and externally threaded lengths ranging from 1 3/4" to 3" depending on the model ( ).

Installation Guidelines

• Inspect bushings for shipping damage before installation ( ).
• Mount bushings externally on the transformer tank or inside cubicles using industry-standard hole patterns and clamping studs ( ).
• Ensure proper gasket placement over the bushing shank to maintain insulation and prevent leaks.
• Compatible with low-voltage cables ranging from 0.5 mm² to 10 mm² using push-in or stud connections ( ).

Electrical Ratings and Safety

• Designed for 1.2 kV class secondary systems, suitable for indoor or cubicle-mounted transformers ( ).
• Provide reliable insulation and mechanical support for low-voltage circuits.
• Proper installation ensures compliance with safety standards and prevents electrical faults or short circuits.

Summary

Secondary distribution box bushings are critical components that connect transformer secondary windings to external circuits safely and efficiently. They combine robust insulation, mechanical strength, and standardized mounting to support reliable low-voltage distribution in residential, commercial, or industrial applications ( ). Proper selection, handling, and installation are essential for long-term performance and safety.