Understanding Low Voltage Busbar Trunking Systems: A Modern Approach to Power Distribution

Introduction

Modern electrical installations demand solutions that balance reliability, adaptability, cost-effectiveness, and safety. The Low Voltage Busbar Trunking System (BTS) has emerged as a superior alternative to traditional cable installations in many applications. The authoritative BEAMA Guide to Low Voltage Busbar Trunking Systems Verified to BS EN 61439-6 provides comprehensive technical guidance on these systems. This article explains key aspects of BTS for contractors, specifiers, and facility managers.

What is a Busbar Trunking System?

A Busbar Trunking System is an enclosed electrical distribution system comprising solid conductors—typically copper or aluminium—separated by insulating materials and housed within a protective enclosure. Available in ratings from around 25 amps up to 6,300 amps, BTS offers a robust alternative to running multiple cables for high-capacity power distribution.

Two Core Applications

BTS installations fall into two main categories:

Distribution Busbar Trunking features tap-off outlets on one or more faces, allowing power to be tapped off at multiple points along the run. This is the most common application, ideal for supplying lighting systems, factory floor distribution, and rising mains in office or apartment blocks.

Feeder Busbar Trunking has no tap-off outlets and serves to interconnect switchboards or connect transformers to switchboards. It is particularly economical for higher current ratings where multiple single-core cables would otherwise be needed.

Why Choose Busbar Over Cable?

Busbar trunking offers several distinct advantages over traditional cable installations:

Installation Efficiency

Contractors can achieve significant savings on materials and labour. Busbar trunking requires fewer fixings per metre than cable, with reduced installation time.

Flexibility and Adaptability

Multiple tap-off outlets provide flexibility to accommodate changing power requirements after initial installation. Repositioning distribution outlets is simpler, and the system is easily extendable.

Space Optimisation

Bends and offsets can be installed in a much smaller area than the equivalent cable run, which requires larger bending radii.

Verified Performance

Busbar trunking systems are engineered products with proven performance verified to recognised international and national standards, including BS EN 61439-6.

Fire Resistance

Busbar trunking systems provide better resistance to the spread of fire, with specific Fire Barrier BTU units designed to prevent fire propagation through building divisions.

Key Components of a Busbar System

A complete busbar installation comprises several standard component types:

Feed Units and End Caps connect the system to the existing electrical network. They can bolt directly into switchboards or be cable-connected via an upstream protective device.

Run Components (straight lengths) form the bulk of the installation, available in standard lengths with custom-engineered options available.

Direction Changes are handled with fixed angle brackets, elbows, tees, and flexible joints that maintain a continuous run.

Tap-Off Units are among the most important components. They distribute power to individual final loads and typically contain overcurrent protection devices such as fuses (BS EN 60269-1), miniature circuit breakers (BS EN 60898), or moulded case circuit breakers (BS EN 60947-2).

Technical Specifications

Short-Circuit Performance

Busbar trunking systems are designed to withstand the effects of short-circuit currents. The short-circuit withstand rating is expressed as:

• Rated short-time withstand current (Icw) – the rms current the system can withstand for a specified period
• Rated peak withstand current (Ipk) – the instantaneous peak current the system can withstand
• Rated conditional short-circuit current (Icc) – when protected by specific short-circuit protective devices

Voltage Drop

Voltage drop figures are provided by manufacturers in mV/A/m format. The calculation considers resistance (which varies with temperature) and reactance. For distributed loads along the trunking, the full load voltage drop may be divided by approximately two to give the approximate voltage drop at the end of the system.

Electromagnetic Fields (EMF)

Busbar trunking systems are often better suited than cables when low magnetic induction is required. The BTS construction facilitates the optimum arrangement of conductors to keep magnetic interference to a minimum. In sandwich-type construction, conductors are closely packed, and induced magnetic fields cancel each other to a large extent, resulting in extremely low external magnetic fields.

Aluminium vs Copper Conductors

Both materials are viable for power busbar trunking systems:

Aluminium offers lower density, resulting in a system approximately 30% lighter than an equivalent copper system, though overall dimensions are typically 10–20% larger.

Copper has higher conductivity, resulting in voltage drop approximately 25% lower and power losses typically 25% lower than aluminium for the same current rating.

Harmonic Considerations

Modern loads with electronic components generate harmonic currents that affect neutral conductor sizing. BS 7671 requires the neutral conductor to be no smaller than line conductors when total harmonic distortion exceeds 15%. For circuits supplying significant electronic single-phase loads, the neutral current can reach 173% of the phase current magnitude.

Busbar trunking manufacturers may provide harmonic-rated systems specifically designed for given harmonic distortion levels without de-rating, or de-rating factors may apply for standard systems.

Installation and Testing

Pre-Installation

All components should be checked for mechanical damage and tested for insulation resistance before installation. Components should be stored in clean, dry conditions with protection from moisture and corrosive materials.

During Installation

Systems must be fixed to the building in accordance with manufacturer's instructions. Joint surfaces must be clean, and torque settings specified by the manufacturer must be used, as current carrying capacity depends on contact pressure.

Post-Installation Verification

Insulation resistance testing should be performed on the complete system. Note that dielectric (flash) tests made on each unit in the factory should not be repeated on an installed system due to safety hazards, unless a specific risk assessment is carried out.

Safe Working

The Electricity At Work Regulations 1989 must be complied with, particularly Regulation 14 regarding work on live conductors. A risk assessment must be carried out for every situation where live working is contemplated.

Standards Compliance

Busbar trunking systems are governed by BS EN 61439-6:2012, which lays down definitions, service conditions, construction requirements, technical characteristics, and verification requirements for low-voltage busbar trunking systems. Other applicable standards include BS EN 61439-1 for general rules, BS 7671 for electrical installation requirements, and BS EN 60529 for degrees of protection (IP Code).

Conclusion

Low Voltage Busbar Trunking Systems offer a proven, efficient, and flexible solution for modern electrical distribution. Their verified performance, installation efficiency, and adaptability make them increasingly preferable to traditional cable installations, particularly in commercial, industrial, and high-rise applications. Understanding the technical specifications, installation requirements, and safety considerations outlined in the BEAMA Guide helps ensure successful specification, installation, and long-term operation of these systems.

Download the complete guide: BEAMA Guide to Low Voltage Busbar Trunking Systems Verified to BS EN 61439-6

Disclaimer: This article provides a summary of a third-party publication produced by BEAMA. While efforts have been made to accurately represent the content, please refer to the official BEAMA Guide to Low Voltage Busbar Trunking Systems Verified to BS EN 61439-6 for complete technical details. Final design, specification, and implementation decisions should be made by qualified electrical engineers and competent professionals in accordance with all applicable regulations and standards.