SS 551:2022 is the Singapore Standard "Code of Practice for Earthing," providing critical guidance on the design, installation, and maintenance of earthing systems for land-based electrical installations. It is a modified adoption of the British Standard BS 7430:2011+A1:2015, tailored to meet local Singaporean regulatory and environmental requirements. Key Purpose and Scope
The primary objective of SS 551 is safety—specifically limiting the potential of current-carrying conductors and non-current-carrying metalwork to prevent electric shock and ensure the proper operation of electrical systems.
Applies to: Land-based installations in and around buildings, including low voltage (LV) systems, high voltage (HV) substation interfaces, and standby generators.
Exclusions: It does not cover ships, aircraft, medical equipment, or functional earthing for electronic components sensitive to static. Major Components of the Standard
The standard is divided into several technical areas that guide engineers through the lifecycle of an earthing system:
Design Principles: Includes guidance on choosing earthing system types like TN-S and TT systems.
Earth Electrodes: Detailed methods for using rods, plates, and horizontal strips to achieve a low-impedance path to the ground.
Soil Resistivity: Guidance on measuring and calculating soil resistance, which is vital for effective electrode placement. ss 551 code of practice for earthing
Substations & Industrial Systems: Requirements for the interface between HV and LV substations and industrial distribution networks.
Documentation: Establishes standards for recording earthing system details to ensure long-term safety and compliance. Notable Updates in the 2022 Revision
The latest version (SS 551:2022) replaced the 2009 edition with several critical additions:
Industrial/Commercial Systems: New Clause 7.2 specifically for these distribution environments.
Safe Working Conductors: Clause 13 provides new guidance on earthing conductors used for safety during maintenance.
Substation Clarifications: Specific updates regarding local utility (electricity and gas) requirements, which take precedence in certain substation scenarios. Practical Implementation
For professionals in Singapore, SS 551 works alongside SS 638 (formerly CP 5, the Code of Practice for Electrical Installations) to ensure comprehensive electrical safety. You can purchase the full standard or a Redline Version (showing changes from the previous edition) at the Singapore Standards e-shop. SS 551:2022 is the Singapore Standard "Code of
The SS 551:2022 is the Singapore Standard "Code of Practice for Earthing," which provides the technical framework for the design, installation, and maintenance of earthing systems in land-based buildings. It is a modified adoption of the British Standard BS 7430. Core Functions and Scope
The standard ensures safety by limiting the potential of current-carrying conductors and non-current-carrying metalwork.
System Earthing: Essential for the proper operation of the electrical system.
Equipment Earthing: Focused on the safety of human life and property by providing a low-impedance path for fault currents.
Application: Applies only to land-based installations in and around buildings; it specifically excludes ships, aircraft, and offshore installations. Key Technical Features
Earth Electrodes: Provides design guidance for various types, including earth rods, plates, and foundation electrodes.
Substation Interface: Details the specific interface requirements between Low Voltage (LV) and High Voltage (HV) substations within buildings. The code discusses TN, TT, and IT systems
Generator Arrangements: Includes rules for protective earthing and changeover switch arrangements for generator sets.
Potential Gradients: Addresses the control of step and touch potentials to prevent electric shock during fault conditions.
Soil Resistivity: Emphasizes site-specific soil resistivity testing and the use of backfill materials to improve contact resistance in rocky ground. Critical Requirements for Compliance SS 551:2022 - Singapore Standards
Note: This review assumes the latest version available (currently SS 551:2018, which supersedes the 2009 edition). If you have an older draft, some clauses may differ, but the core principles remain.
SS 551 requires the following tests upon completion and periodically thereafter:
| Test | Method | Acceptance Criteria | |------|--------|----------------------| | Earth electrode resistance | 3-terminal or 4-terminal fall-of-potential method | ≤ design value (typically ≤ 1 Ω for LV supplies) | | Earth fault loop impedance (Zs) | Loop impedance tester at furthest point | Zs ≤ 0.8 × (Uo / Ia) where Ia = operating current of protective device | | Continuity of protective conductors | Low-resistance ohmmeter (200 mA – 10 A) | R ≤ 0.1 Ω (typical for short bonding runs) | | Touch voltage measurement | Voltmeter between exposed conductive part and reference earth | ≤ 50 V AC | | RCD testing | Dedicated RCD tester | Tripping time ≤ 300 ms (general); ≤ 40 ms for 30 mA RCD) |
All test results must be recorded in an Electrical Installation Test Report (as per SS 638 / EMA requirements).
Based on industry audits, frequent SS 551 violations include: