Earthing is a critical aspect of electrical safety in installations, ensuring that any exposed conductive parts are properly grounded to prevent electrical shocks or fire hazards. However, there is often confusion regarding the correct application of earthing requirements, especially when earth terminals are found unused in some installations. This document aims to clarify the circumstances under which earthing is required, referencing relevant clauses from Australian Standards AS/NZS 3000:2018 and AS/NZS 5139:2019, and to determine whether unused earth terminals pose a safety risk.

Unused Earth Terminals?

In various electrical installations, it has been observed that some earth terminals are left unused. This has led to questions about whether these situations are safe or if they contravene safety standards. The confusion primarily arises because the necessity for earthing depends on several factors:

1. The protection class of the device.
2. The Decisive Voltage Classification (DVC) of the system.
3. The section of the standard applicable to the system (e.g., Section 4 or Section 5 of AS/NZS 5139:2019).
4. The manufacturer’s earthing strategy.

Different types of equipment and systems—such as Class I or Class II devices, or systems with varying Decisive Voltage Classifications (DVCs)—have distinct earthing requirements. Additionally, manufacturers may provide unclear or varied instructions about when and how to implement earthing, leading to discrepancies in practice. Furthermore, differing sections of the standards, such as AS/NZS 3000:2018 and AS/NZS 5139:2019, specify earthing requirements in various ways depending on system design and voltage levels, contributing to the uncertainty.

Relevant Standards and Clauses

AS/NZS 3000:2018 – Electrical Installations (Wiring Rules)

AS/NZS 3000:2018, also known as the Wiring Rules, provides comprehensive requirements for the safe design, installation, and verification of electrical installations. Key sections and clauses relevant to earthing include:

• Section 1: Equipment Classifications and Earthed Situations
  • Clause 1.4.31, 1.4.32, 1.4.33, 1.4.48, and 1.4.50: These clauses define terms such as “protective earth,” “exposed conductive parts,” and classifications of electrical equipment based on their construction and the necessity for earthing.
• Section 5: Earthing Arrangements and Earthing Conductors
  • Clause 5.4.1.1: This clause mandates that exposed conductive parts of electrical equipment must be earthed if:
    • The equipment is installed or could operate in an earthed situation, or
    • The equipment is not in an earthed situation, but any exposed conductive part is electrically continuous with an extraneous conductive part that is in an earthed situation.
    • The clause further states that exposed conductive parts should not be earthed in cases where the equipment is protected by electrical separation (Clause 7.4.3(c)) or when supplied by a Safety Extra Low Voltage (SELV) or Protective Extra Low Voltage (PELV) system, as per Clause 7.5.
  • Exceptions for Double Insulation: Clause 5.4.1.1 also provides exceptions where earthing is not required if:
    • Electrical equipment complies with AS/NZS 3100 for double insulation.
    • Internal wiring within the equipment is protected to prevent contact with accessible conductive parts.
• Section 7: Special Electrical Installations
  • Clause 7.3.6: Specifies that any exposed conductive parts of an electricity generation system must be earthed by connection to the main earthing conductor at the main switchboard.

AS/NZS 5139:2019 – Electrical Installations – Safety of Battery Systems for Use with Power Conversion Equipment

AS/NZS 5139:2019 provides specific guidelines for the safety of battery systems and their installation, including earthing requirements:

• Clause 4.3.1.3.1: Emphasizes that the earthing of a pre-assembled integrated Battery Energy Storage System (BESS) must follow both the manufacturer’s earthing requirements and the earthing requirements specified in AS/NZS 3000.
• Clause 5.3.1.6 and Clause 5.3.1.7: These clauses define earthing arrangements for pre-assembled battery systems, specifying various configurations depending on whether the system is separated or non-separated and the relevant Decisive Voltage Classification (DVC).
• Clause 6.3.1.7: Similar to Clause 5.3.1.7 but applies to battery systems not covered in Sections 4 or 5, reinforcing the importance of following manufacturer instructions and appropriate earthing according to the DVC.

Decisive Voltage Classification (DVC)

The DVC (DVC A, DVC B, DVC C) determines the voltage levels within an installation and, consequently, the requirements for insulation and earthing to ensure safety. Higher DVC levels typically require more stringent safety measures, including earthing. Of particular relevance is Note 2 in Table 3.2 of the AS/NZS5139:2019 which states that DVC-B and DVC-C are treated as LV as defined in the AS/NZS3000.

Factors Influencing the Need for Earthing

The necessity of earthing specific components in an installation depends on the following:

1. Protection Class of the Device: Electrical equipment is classified based on the level of protection against electric shock it provides. For instance, Class I equipment must have exposed conductive parts earthed, while Class II equipment, which has double insulation, does not require earthing under certain conditions.
2. DVC Class of the System: The DVC determines the voltage at which the system operates, influencing the level of insulation and the necessity of earthing. Higher voltage systems generally require more rigorous earthing protocols to ensure safety.
3. Applicable Section of the Standard: AS/NZS 5139:2019 outlines different requirements based on the section relevant to the installation (e.g., Section 4 vs. Section 5). These sections define the specific earthing needs based on system design and voltage levels.
4. Manufacturer’s Earthing Strategy: Manufacturers may provide specific instructions for earthing their equipment. These guidelines are crucial for ensuring the safety and compliance of installations, especially for pre-assembled systems like BESS.

Conclusion: Assessing the Safety of Unused Earth Terminals

Whether unused earth terminals in an installation are unsafe depends on the factors outlined above. In many cases, not using an earth terminal is not inherently unsafe, provided that:

• The equipment is correctly classified and meets the conditions specified in AS/NZS 3000:2018 and AS/NZS 5139:2019.
• The system design aligns with the appropriate DVC and follows manufacturer guidelines.
• Proper insulation and protective measures are in place, such as double insulation or the use of SELV/PELV systems.

However, neglecting to use an earth terminal when it is required by the standards or manufacturer instructions can lead to significant safety risks, including electric shock and fire hazards. Therefore, it is imperative to thoroughly understand and adhere to the earthing requirements specific to each installation.

Recommendations

1. Site Assessment: Conduct a thorough assessment of the installation to determine the correct earthing requirements based on equipment protection class, system DVC, and applicable standards sections.
2. Compliance with Standards: Ensure all installations comply with the relevant clauses of AS/NZS 3000:2018 and AS/NZS 5139:2019, particularly regarding earthing arrangements.
3. Consult Manufacturer Guidelines: Always follow the manufacturer’s earthing strategy and instructions, as these are designed to ensure the safety and functionality of the equipment.
4. Training and Awareness: Provide training to installers and technicians on the importance of proper earthing practices and the potential risks associated with unused earth terminals when earthing is required.

By following these recommendations, electrical installations can be ensured to be safe, compliant, and effective in minimizing risks associated with improper earthing practices.

Examples

The following photo on the shows an example of where external earth terminals are not used.  This system is non-compliant and rectification would be required.

The following excerpt is from the Sungrow SH8.0RS User Manual, which relates to the photo above.  This provides a clear example of why external earth terminals must be used.