Protecting electrical systems has become more complex as power now frequently flows in multiple directions. Recent findings from BEAMA's 2024 technical bulletin highlighted critical safety concerns with protective devices failing under bidirectional current flow. This is particularly relevant for installations with multiple power sources, where current direction can vary. To ensure safety and compliance, protective devices must now demonstrate reliable operation regardless of current direction, marking a significant shift in how we approach circuit protection.

A Critical Update to Wiring Regulations

Amendment 3 to BS 7671:2018, effective July 2024, introduces new standards for bidirectional power flow in electrical installations. The key addition, Regulation 530.3.201, requires electrical designers and installers to consider current flow direction when selecting protective devices.

Two types of protective devices are now formally defined:

  • Bidirectional devices: Accept power supply connections at either or both terminal sets
  • Unidirectional devices: Allow power supply connection at only one specific terminal set

This regulatory update reflects the growing complexity of modern electrical systems where power can flow in multiple directions, particularly in installations with renewable energy sources, battery storage, or electric vehicle charging capabilities.

Understanding Device Labeling and Selection

Protective devices use specific labeling to indicate their capabilities:

Unidirectional Devices:

  • Marked with 'In/Supply' and 'Out/Load'
  • Suitable only for installations with a single power source
  • Must be connected according to labeling

Bidirectional Devices:

  • Labeled with 'L/N' or 'L1/N1' and 'L2/N2'
  • No specific in/out markings
  • Required for systems with multiple power sources (solar, EV charging, battery storage)

Selecting the correct device type is crucial - unidirectional devices can fail if used in systems with multiple power sources.

Understanding Power Flow in Solar PV Systems

Single Power Flow Scenarios In basic solar PV installations without battery storage, power flows in one direction - from the PV panels through the inverter to the consumer unit. Despite this unidirectional power flow, Regulation 530.3.201 requires bidirectional protective devices since the inverter supply connects to the load side while grid supply connects to the supply side.

Multiple Power Flow Scenarios When battery storage is added, power flow becomes more complex:

  • Solar PV can power the grid or charge batteries
  • Grid power can charge batteries
  • Batteries can supply power to the installation

This bidirectional power flow necessitates bidirectional protective devices to ensure safety and compliance with Regulation 826.1.2.2, which requires consideration of all current flow directions in prosumer installations.

Additional Safety Requirements for Bidirectional Systems

RCD and Thermal Protection Standards:

  1. Protection against thermal effects and overcurrent must remain effective regardless of power flow direction
  2. RCDs providing additional protection must disconnect all live conductors, including the neutral

For solar PV and similar installations, this means protective devices must have neutral switching capability. This requirement ensures complete isolation of all conductors when needed, enhancing safety in bidirectional power scenarios.

Inspection Standards for Modern Electrical Systems

Periodic inspection criteria have evolved to address bidirectional power systems. Inspectors must now evaluate the correct application of unidirectional/bidirectional devices and assign appropriate classification codes:

  • Code 2: For serious concerns requiring urgent attention
  • Code 3: For situations needing improvement but not urgent
  • Code 1: Rarely needed, reserved for immediate danger situations

As prosumer installations become more common, industry guidance recommends defaulting to bidirectional protective devices for future-proofing and compliance. Inspectors should consult current industry guidance for accurate code classification.

Protective Device Types: Key Differences

Unidirectional Devices:

  • Handle one-way power flow (supply to load)
  • Marked with line/load terminals
  • Often use electronic circuits for protection
  • Require precise connection per manufacturer specs

Bidirectional Devices:

  • Handle two-way power flow
  • No line/load markings needed
  • Work with renewable energy and storage systems

Proper device selection ensures system protection while accommodating modern power flow requirements.

Why Bidirectional Protection Matters

Modern renewable systems demand bidirectional protection due to complex power flows. Here's why:

Solar Systems:

  • Power flows from panels to grid
  • Protection needed in both generation and consumption modes
  • Traditional unidirectional devices may fail

Energy Storage:

  • Batteries both charge and discharge
  • Two-way current flow requires two-way protection
  • Safeguards needed for storing and releasing energy

Bidirectional devices protect against faults regardless of current direction, making them essential for renewable installations.

Where Bidirectional Devices Are Used

Solar Power Integration Modern solar installations require robust protection for both energy generation and consumption. Bidirectional devices safeguard the system whether power flows from panels to the grid or vice versa, ensuring consistent protection during all operating modes.

Energy Storage Solutions Battery systems constantly switch between charging and discharging states. Bidirectional devices provide seamless protection during both operations, maintaining safety as energy flows to and from storage units.

EV Charging Infrastructure Electric vehicle charging stations increasingly offer vehicle-to-grid capabilities. Bidirectional protection is essential for managing power flow during charging and when vehicles feed energy back to the grid.

Microgrid Applications Complex microgrids juggle multiple power sources and directions. Bidirectional devices provide unified protection across these varied power flows, enabling reliable operation of self-contained power networks.

Hybrid Renewable Systems When multiple renewable sources work together, power flows become intricate. Bidirectional protection ensures safety across all system configurations, supporting the integration of diverse energy sources.

Which Circuit Breakers are Bidirectional?

Some MCBs and RCDs are bidirectional as standard, some manufacturers such as FuseBox and Elucian have produced new RCBOs to meet latest standards.  Some FuseBox and Elucian RCDs, RCBOs and MCBs that are bidirectional can be found below:

Conclusion

In conclusion, bidirectional and unidirectional protective devices are essential for ensuring electrical safety in modern electrical systems. Bidirectional protective devices, in particular, are crucial for renewable energy systems, as they offer enhanced safety and flexibility. Understanding the differences between bidirectional and unidirectional protective devices is critical for selecting the right device for a particular application.

Bidirectional devices have a wide range of applications in modern electrical systems, including solar power systems, energy storage systems, and electric vehicle charging stations. Energy storage systems, in particular, require special safety considerations, including bidirectional protective devices, thermal management, and electrical insulation.

By understanding the importance of bidirectionality in renewable energy systems and the applications of bidirectional devices, electrical engineers and technicians can design and install safe and efficient electrical systems that meet the needs of modern electrical applications.