ELECTRIC KOREA · GROUNDING & FIELD PRACTICE
How South Korea moved beyond the former Class 1–3 terminology—and why one resistance value never tells the whole story
A grounding conductor can look like the quietest wire in an electrical room. Years ago, I watched that assumption fail in an instant: while equipment installation was operating, a coworker loosened a grounding connection and a visible spark appeared as the conductor separated.
We did not measure the current at that moment, so I cannot identify its exact source or magnitude. What the incident established was simpler and more important: a grounding or bonding conductor must never be assumed to be electrically inactive, and it must not be casually disconnected from an energized installation.
That field experience also explains why grounding cannot be reduced to a green wire or a memorized resistance value. In South Korea, the language has shifted from the former Class 1, Class 2, Class 3, and Special Class 3 grounding-work classifications toward the broader protection framework used by the Korean Electrical Code (KEC).
What Grounding Actually Does
Grounding, or earthing, intentionally connects a point in an electrical system or exposed conductive parts to earth through a designed conductive path. Its purpose is not simply to “send electricity into the ground.”
During an insulation fault, the grounding and protective-conductor system helps control dangerous potential differences and supports the operation of the selected protective measures. Depending on the installation, it can establish a system reference, support equipotential bonding, limit voltage rise, provide part of a fault-current path, and reduce electric-shock risk.
The critical phrase is depending on the installation. The behavior of a TN system is not identical to that of a TT or IT system, and an earth electrode resistance measurement answers only one part of the protection question.
From the Former Korean Classes to the KEC Framework
Experienced Korean electricians still recognize the former expressions “Class 1,” “Class 2,” “Class 3,” and “Special Class 3” grounding. Under that earlier classification, familiar resistance values included 10 Ω or less for Class 1, 100 Ω or less for Class 3, and 10 Ω or less for Special Class 3; the Class 2 requirement depended on system conditions and earth-fault current.
Those terms remain part of field conversation and historical documentation, but they should not be used as if they were the primary structure of the modern KEC.
Three questions make the modern terminology easier
TN, TT, and IT in brief
TN: One point of the supply system is directly earthed, and exposed conductive parts are connected to that point through protective conductors. TN-S, TN-C, and TN-C-S describe how neutral and protective functions are separated or combined.
TT: One point of the supply is earthed, while exposed conductive parts of the installation are connected to a local earthing arrangement that is electrically independent of the supply electrode.
IT: The supply is isolated from earth or connected through an impedance, while exposed conductive parts are earthed according to the protection design.
Two Different Grounding Roles in One Transformer Installation
The photographs below show why the terminology matters. In the first installation view, the green conductor associated with the transformer neutral point illustrates system earthing: earthing a point in the power system.
The next view shows grounding conductors connected to the metal enclosure and other exposed conductive parts. Those connections belong to the protective earthing function intended to limit dangerous touch voltage and support fault protection.
Why Ground Resistance Still Matters
Ground resistance is an important characteristic of an earth electrode or grounding system. A lower value can help limit earth-potential rise and support the intended performance under fault conditions. But the statement “below 10 Ω means the installation is safe” is too simple.
The result must be interpreted together with the earthing arrangement, fault-current path, protective-conductor continuity, equipotential bonding, protective-device characteristics, and the required automatic-disconnection conditions. The applicable KEC provisions depend on the actual installation.
Measurements can change with soil resistivity and moisture, corrosion, loose connections, electrode deterioration, damaged conductors, and later excavation or construction. Grounding therefore cannot be treated as something installed once and forgotten.
Field example: 9.9 Ω
While preparing a new agricultural electrical service, I installed the grounding electrode and measured the completed work. The tester displayed 9.9 Ω.
This number records one installation under its own conditions. It is not a universal design target or automatic proof of safety. The professional task is to install correctly, measure correctly, and decide what the result means within the protection design and applicable requirements.
The Spark at the Grounding Terminal
The incident mentioned at the beginning occurred while equipment was operating. A coworker loosened a grounding connection, and a visible spark appeared when the connection separated. Because no current measurement or follow-up investigation was performed at that moment, assigning a specific cause would be speculation.
Possible operating currents and potential differences depend on the installation, connected equipment, bonding paths, leakage characteristics, and other site conditions. Regardless of the precise cause, opening the connection removed part of an essential protection path while the installation was energized.
What an Inspection Must Look Beyond
A conductor and terminal may appear normal even when the effective grounding path has been weakened by corrosion, loose connections, damage, electrode deterioration, or later modifications. Visual inspection is necessary, but it cannot establish every electrical property.
Depending on the installation and inspection scope, the evaluation may require earth-resistance measurement, protective-conductor continuity verification, review of bonding, confirmation of the fault path, and verification that the protective device can disconnect the supply as required.
This is the larger change in thinking. Instead of asking only “What class is this?” or “Is it below 10 Ω?”, the engineer must ask:
- Where will fault current flow?
- What touch voltage could appear on exposed conductive parts?
- Is the protective conductor continuous?
- Is equipotential bonding correctly established?
- Will the selected protective device operate within the required conditions?
- Does the complete system still perform as intended?
Conclusion
South Korea’s former grounding classes remain useful historical language, but they are not direct substitutes for the modern KEC concepts of system earthing, protective earthing, grounding arrangements, and TN, TT, or IT systems.
A low resistance value is valuable evidence, not a complete safety verdict. A green conductor is part of the protection system, not an inactive spare wire. The most reliable understanding comes from seeing grounding, bonding, protective conductors, fault-current paths, protective devices, automatic disconnection, and inspection as one coordinated system.
Safety and technical scope
This article explains general concepts and records field experience. It is not a design specification or authorization to work on energized equipment. Each installation must be designed, constructed, tested, and maintained by qualified personnel according to the current KEC, related requirements, equipment instructions, and actual site conditions.
Reference: Korea Electric Association, Korean Electrical Code (KEC) portal. Always consult the current text and applicable project requirements rather than relying on this explanatory article alone.
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