Ground / Earth Symbol
Definition: The Ground / Earth symbol represents a reference node connected to the Earth via a grounding electrode — providing a zero-volt potential reference and a fault-current return path to the soil — as defined in IEC 60617 (database reference S00196, the 'earth electrode' symbol) and IEEE 315-1975 (ANSI Y32.2), Section 3.10, where it is drawn as three horizontal lines of decreasing length beneath a horizontal bar.
Also known as: earth ground, protective earth, PE, safety ground, earth electrode, true earth, ground (earth), ⏚ (Unicode U+23DA).
What the Ground / Earth symbol means
The Ground / Earth symbol denotes the point in a circuit that is physically connected to the Earth's conductive soil through a grounding electrode system — typically a copper-clad ground rod, buried ring conductor, or building structural steel. This connection establishes a stable 0 V reference that is independent of circuit currents, and provides a low-impedance return path for fault currents so that overcurrent protection devices (fuses, breakers) operate correctly when a live conductor contacts the earthed chassis or enclosure.
In wiring diagrams the Ground / Earth symbol (GND pin) also denotes the protective earth (PE) conductor — the green/yellow wire in IEC wiring or the bare or green wire in NEC wiring — that bonds all exposed conductive parts of equipment to earth. This protective conductor does not carry load current under normal operation; it carries fault current only when an insulation failure occurs, diverting that current safely to earth and away from personnel.
How to identify the Ground / Earth symbol
The Ground / Earth symbol is drawn as a horizontal line (representing the earth connection point) with three horizontal lines of successively shorter length stacked below it, like a downward-pointing ladder or comb. This three-bar descending arrangement is the internationally recognised Earth Ground glyph (Unicode ⏚, U+23DA). It is visually distinguished from the Chassis Ground symbol (diagonal/oblique downward arrowhead lines) and the Signal/Common Ground symbol (a single downward-pointing solid triangle or single line with a point).
Function in a circuit
The Ground / Earth connection provides three critical functions in electrical systems. First, it establishes the system voltage reference: all other voltages in the circuit are measured relative to the earth node (0 V). Second, it provides a fault-current return path: if a live conductor contacts an earthed enclosure, current flows through the PE conductor to earth and back through the supply transformer neutral, causing the overcurrent device to trip. Third, it provides lightning and surge protection: transient overvoltages (from lightning, switching, or static discharge) are conducted to earth through surge protective devices connected between the line conductors and earth ground.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617 database symbol S00196 defines the earth electrode (Earth Ground) symbol as three horizontal lines of decreasing length below a horizontal connection line. IEC 60364 (Low-voltage electrical installations) and IEC 62305 (Lightning protection) govern the design of earthing systems. The Unicode character ⏚ (U+23DA, EARTH GROUND) is the text representation of this symbol. |
|---|---|
| ANSI/IEEE 315 | IEEE 315-1975 (ANSI Y32.2), Section 3.10, defines the Earth Ground symbol as three horizontal lines of decreasing length arranged like a downward-pointing comb. NFPA 70 (NEC) Article 250 governs grounding and bonding requirements in North America, including the requirement for grounding electrode conductors to be copper of minimum specified cross-section. |
| Key difference | The IEC and IEEE/ANSI Earth Ground symbols are visually identical — both use three horizontal bars of decreasing length. The primary distinction in practice is that IEC 60617 explicitly labels the symbol as 'earth electrode' with reference S00196, while IEEE 315 uses the term 'earth' or 'ground'. North American practice (NEC) distinguishes between 'grounding' (connecting to earth) and 'bonding' (connecting metal parts together); IEC 60364 uses 'earthing' for both concepts. |
Terminals / pins
| Pin | Name |
|---|---|
| gnd | GND |
Typical values
Earth electrode resistance: NEC Article 250.53 requires a ground rod to achieve ≤25 Ω; IEC 60364-5-54 requires ≤10 Ω for TT systems. PE conductor size: 16 mm² copper minimum for bonding to earth electrode per IEC 60364; 6 AWG copper minimum for residential electrode conductor per NEC 250.66. Earth fault loop impedance: typically 0.1–2 Ω for TN-S systems to ensure breaker/fuse operation within 0.4 s per IEC 60364-4-41.
Where the Ground / Earth symbol is used
- Residential and commercial panel boards — the earth ground bus bar connects all equipment grounding conductors and the grounding electrode conductor to the earthing system
- Power electronics schematics — the earth ground symbol marks the chassis-to-earth bonding point and the reference node for mains-voltage measurements
- Lightning protection systems — surge protective devices (SPDs) connect L, N, and PE conductors to earth ground to divert transient overvoltages per IEC 62305 and NFPA 780
- AC power supply circuits — the safety earth conductor (green/yellow wire) connects the IEC inlet PE pin to the chassis and to the earth ground node in the schematic
- Medical equipment schematics (IEC 60601-1) — protective earth is a mandatory connection for Class I equipment; the earth ground symbol identifies the PE terminal on the power inlet
- Telecommunications and data centres — earthing networks use the earth ground symbol to show connections to building earth electrodes, reducing common-mode noise on signal cables
- Outdoor electrical installations — underground metallic conduits, equipment pads, and transformer tanks are shown connected to earth ground for lightning and fault protection
Example
In a residential single-phase service entrance schematic, the Earth Ground symbol (GND pin) is shown connected at the main panel neutral-ground bond point. A grounding electrode conductor (6 AWG bare copper) runs from this node to two 2.4 m copper-clad ground rods driven into the soil 1.8 m apart. All equipment grounding conductors from branch circuits converge at the earth ground node, which is labelled with the Earth Ground symbol (three descending horizontal bars) to distinguish it from the signal and chassis ground references elsewhere in the diagram.
Key facts
- The Ground / Earth symbol (⏚, Unicode U+23DA) is drawn as three horizontal lines of decreasing length stacked below a horizontal connection line, representing a physical connection to the Earth via a grounding electrode, as defined in IEC 60617 reference S00196 and IEEE 315-1975 (ANSI Y32.2) Section 3.10.
- The Ground / Earth symbol has a single electrical connection pin labelled GND (id: gnd), representing the node bonded to the Earth electrode system.
- Earth Ground establishes the system 0 V reference and provides the fault-current return path so overcurrent devices (fuses, breakers) operate when live conductors contact earthed metal, protecting personnel from electric shock.
- The protective earth (PE) conductor — green/yellow in IEC systems, green or bare in NEC systems — is the physical wire that connects equipment to the earth ground node; it carries no load current under normal operation.
- NEC Article 250.53 requires a ground rod to achieve a resistance to earth of 25 Ω or less; IEC 60364-5-54 requires 10 Ω or less for TT earthing systems.
- Earth Ground (⏚) is visually distinct from Chassis Ground (diagonal arrowhead lines) and Signal Ground (inverted triangle); all three symbols represent 0 V reference nodes but with different physical connections and purposes.
- IEC 60617 uses the keyword 'earth' (rather than 'ground') for the symbol, reflecting European electrical terminology; ANSI/IEEE 315 uses both 'earth' and 'ground' interchangeably for the same three-bar symbol.
Diagrams that use this symbol
Frequently asked questions
What does the earth ground symbol look like?
The Earth Ground symbol is drawn as three horizontal lines of successively shorter length stacked below a horizontal bar, resembling a downward-pointing comb or ladder. In Unicode text it is represented by ⏚ (U+23DA, EARTH GROUND). This is defined in IEC 60617 (reference S00196) and IEEE 315-1975.
What does the ground / earth symbol mean in a circuit diagram?
The Ground / Earth symbol means the circuit node is physically connected to the Earth via a grounding electrode (ground rod, building steel, etc.). It establishes the 0 V reference for the circuit and provides a fault-current return path to earth so that overcurrent devices operate when insulation faults occur, protecting personnel from lethal shock.
What is the difference between earth ground and chassis ground symbols?
Earth Ground (three horizontal decreasing-length bars, ⏚) represents a physical connection to soil via a grounding electrode. Chassis Ground (diagonal downward arrowhead lines) represents a connection to the equipment's metal enclosure, which may or may not be bonded to Earth. In properly designed mains-powered equipment, chassis and earth ground are bonded together at a single point.
What standard defines the earth ground symbol?
The Earth Ground symbol is defined in IEC 60617 (database reference S00196, 'earth electrode') for international schematics and in IEEE 315-1975 (ANSI Y32.2), Section 3.10, for North American engineering drawings. Both standards show the same three-bar descending horizontal-line glyph. The Unicode text equivalent is ⏚ (U+23DA).
What is the colour of the earth ground wire?
In IEC wiring (Europe, most of the world), the protective earth conductor is insulated with green and yellow stripes, per IEC 60446. In North American NEC wiring, the equipment grounding conductor is bare copper, green, or green with one or more yellow stripes, per NEC Article 250.119. These conductors connect the equipment chassis to the Earth Ground symbol node in the schematic.
Does earth ground carry current under normal operation?
No. The protective earth (PE) conductor connected to the Earth Ground symbol carries no load current under normal operation. It only carries fault current when a live conductor contacts an earthed enclosure or metal part, diverting that current to earth so the overcurrent protection device (fuse or breaker) can detect and clear the fault.
What is the required resistance of an earth ground electrode?
NEC Article 250.53 requires a grounding electrode (ground rod) to achieve 25 Ω or less to earth; if one rod exceeds 25 Ω, a second rod must be installed. IEC 60364-5-54 requires 10 Ω or less for TT earthing systems. Lower resistance (1–5 Ω) is preferred for industrial and telecommunications facilities for better surge protection and fault-loop performance.
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