11.1 Introduction

With the development of epoxy resins as an insulation material for the switchgear component and the establishment of Busways as a viable alternative to Busducts in certain areas of application, it was but natural to explore the possibility of developing a cast resin bus for low & medium voltage applications. While the application of Busways is limited to its usage in low voltage distribution, CRB offered an opportunity to extend its application to medium voltage distribution.

The need was driven more for making CRB with the following desirable features:

• Maintenance-free.
• A higher degree of protection up to IP 68.
• Immune to corrosive & hazardous atmosphere.
• Resistant to U/V Radiations.
• Underground Installation in trenches or buried and avoid elevated road crossings.
• Fire Stop (up to 3-hour rating) as an inherent feature.
• Self-extinguishing insulation, and is halogen-free, non-flammable, and emits no toxic gas.
• Most compact for medium voltage.
• Higher tolerance in site joints up to 6 mm (1/4”).

CRBs have most of the features attributable to Busways. Despite being more expensive than Busducts and Busways of similar ratings, they are preferred in projects that require a higher degree of environmental protection.

CRBs are manufactured with embedded Aluminium or Copper conductors. These are manufactured up to a rating of 6300 A with Copper conductors and 5000 A with Aluminium conductors for low voltage applications. These are also manufactured up to a rating of 3000 A with Aluminium conductors and 4000 A with Copper conductors for medium voltage application up to 36 kV.

Unlike in Busways where the conductors are wrapped/coated with insulation and pressed together along with the enclosure, in a CRB there is a specific gap that is maintained between the conductors, to be filled in with resin for insulation. The gap size will depend upon the insulation level of the CRB. For higher rated voltage, individual phase conductors are separated by a significant distance, tied to the adjacent conductor by resin tie rods at strategic locations and cast together. The heat generated by the conductor is conducted across the resin and dissipated.