Ss 551 Code Of Practice For Earthing Site
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).
The Main Earthing Terminal (MET) is the central hub where all earth conductors meet.
Connections to the MET must include:
Sizing of Protective Conductors: SS 551 provides two methods for sizing protective conductors (PE):
SS 551 includes specific clauses for:
SS 551 adopts the IEC classification of earthing systems using two-letter codes:
Electricity is a desperate creature; it always seeks the path of least resistance to return to its source. In a perfect system, that path is the wiring. But when lightning strikes a skyscraper, or a fault sends current surging through the casing of an industrial machine, electricity looks for a chaotic exit. ss 551 code of practice for earthing
SS 551 is the protocol for catching that runaway energy.
Developed by Enterprise Singapore and aligned closely with international IEC standards, SS 551 dictates how we create a "reference potential"—essentially a zero-voltage safety zone. It moves beyond the rudimentary "connect wire to ground" philosophy of the past into a sophisticated regime of soil resistivity analysis, touch voltage limits, and electromagnetic compatibility.
"Most people think earthing is just a safety dump," says a senior electrical consultant involved in major infrastructure projects. "But SS 551 is about stability. It’s about ensuring that your sophisticated medical equipment in a hospital doesn't fry because of a voltage spike next door. It’s about signal integrity as much as it is about human safety."
Contrary to old myths, SS 551 prohibits isolated "clean earth" rods that are separated from the main earthing system. All equipment must reference a single-point earth to prevent ground loops. The standard recommends a mesh or grid earthing system under raised floors, bonded to the structural steel. SS 551 requires the following tests upon completion
Using the fall-of-potential method (3-pole or 4-pole tester):
SS 551 mandates the use of earth electrodes to dissipate fault current into the general mass of the earth.
Types of Electrodes:
Requirements:
