Earthing Diagram: Plate, Pipe, and Strip Earthing Explained

Earthing (called grounding in North American practice) is the deliberate electrical connection of equipment, enclosures, and structural metalwork to the general mass of earth. A good earth path limits touch voltages during a fault, causes protective devices to operate quickly, and provides a low-impedance reference for electrical systems. This guide covers the three main earthing electrode types -- plate, pipe, and strip -- along with earth pit construction, resistance targets, and the relevant context from IS 3043 (Indian Standard for earthing practice, widely referenced in industrial projects alongside IEC and BS 7430).

Why Earthing Matters

Without a reliable earth path, a phase-to-ground fault on exposed metalwork raises the enclosure to line voltage relative to true earth. Anyone touching the enclosure while standing on the ground completes the circuit. With proper earthing:

• Fault current flows through the earth conductor instead of through a person
• The fault current is large enough to operate the fuse or circuit breaker within the protective device's clearing time
• Residual current devices (RCDs / GFCIs) can detect the fault current and trip in milliseconds
• Lightning surge currents are directed safely to earth

The target earth electrode resistance varies by system, but general guidance from IS 3043 and BS 7430 is:

• Major substations / transformer neutrals: below 1 ohm
• General LV distribution: below 5 ohms
• Individual equipment earth: below 10 ohms

In high soil resistivity areas (rocky ground, dry sandy soil), achieving these values requires multiple electrodes in parallel or chemical enhancement of the soil.

Plate Earthing

Construction

Plate earthing uses a metal plate -- typically galvanized iron (GI) or copper -- buried vertically in the ground.

Standard dimensions (IS 3043):

• GI plate: minimum 600 mm × 600 mm × 6 mm thick
• Copper plate: minimum 600 mm × 600 mm × 3 mm thick

The plate is buried with its top edge at least 3 m below ground level (deeper is better -- soil moisture and conductivity improve with depth). The plate is surrounded with a 150 mm layer of alternate charcoal (coke) and common salt to reduce contact resistance and retain moisture.

Components of a Plate Earthing System

1. Earth plate: GI or copper, minimum size as above
2. Earth conductor: 25 mm × 6 mm GI flat strip (or 35 mm² copper conductor) connected to the plate
3. Earth pit: A masonry chamber above ground that provides inspection access and a water inlet
4. GI pipe riser: Carries the earth conductor from the plate up through the pit to the surface
5. Inspection cover: Cast iron or concrete pit cover
6. Watering pipe: 12 mm to 19 mm GI pipe with funnel top, for periodic water treatment of the earth electrode

Plate Earthing Diagram -- Key Elements

The earth conductor connects from the equipment to the earth plate via a GI conduit or direct burial. At the pit, a GI nut and bolt clamp joins the equipment earth wire to the flat strip. A disconnecting link at the pit allows earth resistance testing with the installation disconnected.

Earth resistance of a single plate (approximate):

The resistance depends on soil resistivity (ρ in ohm-meter). For a 600 mm square plate at depth:

R ≈ ρ / (4 × plate dimension) -- simplified formula for a square plate

At ρ = 100 ohm-m (average soil): R ≈ 100 / (4 × 0.6) ≈ 42 ohms for a single plate. Multiple plates in parallel or salt treatment reduces this significantly.

Pipe Earthing

Construction

Pipe earthing is the most common method for building and industrial earthing because it is compact, easy to install in variable-depth configurations, and achieves low resistance in moderate soil conditions.

Standard pipe dimensions (IS 3043):

• GI pipe: minimum 38 mm (1.5 inch) nominal bore, 2.5 m to 3 m length
• Perforations: Small holes drilled along the lower portion of the pipe allow moisture and salt solution to seep into the surrounding soil

The pipe is driven or buried vertically. The top of the pipe is terminated in an inspection pit with a connecting clamp.

Surrounding Fill

The pipe is surrounded with a mixture of:

• Charcoal: Improves conductivity, retains moisture
• Common salt (NaCl): Reduces soil resistivity around the electrode
• Coke: Provides a conductive packing medium

For high resistivity soil, bentonite clay is used in place of or in addition to salt/charcoal -- bentonite expands when wet, maintains contact with the electrode, and has low resistivity.

Pipe Earthing Diagram -- Key Elements

Ground level
    |
  [GI Pipe Inspection Chamber / Pit]
    |  -- [disconnecting link]
    |  -- [earth lead connection point]
    |
  [GI Conduit protecting earth conductor]
    |
  [GI Pipe electrode, 38mm bore, 2.5--3m long]
  [surrounded by charcoal / salt / coke filling]

Multiple pipe electrodes in parallel reduce overall resistance. Two pipes 6 m apart (spacing should be at least the pipe length) have combined resistance of approximately R₁/2 × a utilization factor (typically 0.65 to 0.75 for two parallel electrodes at equal spacing equal to rod length).

Strip (Horizontal) Earthing

Construction

Strip earthing uses a long metallic strip or bare conductor buried horizontally at shallow depth (0.5 m to 1.0 m). It is preferred for:

• Rocky ground where driving a pipe is impractical
• Large sites where a grid (mesh) earth is required (substations, industrial plants)
• Supplementing other electrode types

Strip materials:

• GI strip: 25 mm × 6 mm minimum cross-section
• Copper strip: 25 mm × 4 mm minimum, or 25 mm² bare copper conductor (solid or stranded)

IS 3043 recommends a minimum length of 15 m for a single strip electrode. Longer strips, radial arrangements, or grid configurations significantly reduce resistance.

Strip Earthing Calculation

Resistance of a horizontal strip (simplified):
R ≈ ρ / (π × L) × ln(2L² / ah) -- where L is strip length, a is conductor radius, h is burial depth

For practical estimates, a 30 m GI strip buried 0.6 m deep in 100 ohm-m soil gives approximately 5 to 8 ohms -- often meeting general equipment earth requirements without enhancement.

Foundation Earth Electrode

Modern buildings increasingly use the reinforced concrete foundation as an earth electrode (also called a foundation earth electrode or Ufer ground in the US). The concrete encases steel reinforcement, which has a very large contact area with the earth and provides excellent long-term resistance values -- often below 1 ohm for a typical building slab. IS 3043:2018 and IEC 62305 both recognize this type.

Earth Resistance Testing

Earth electrode resistance must be measured before a system is commissioned and periodically thereafter (annually for critical systems, typically every 3 years for standard installations).

Fall-of-Potential (Three-Point) Method

The standard test method:

1. Disconnect the electrode under test from all bonding connections
2. Drive a current stake (C2) at a distance of at least 10× the electrode depth (30 m minimum for a 3 m pipe)
3. Drive a potential stake (P2) at 62% of the distance between the electrode and C2
4. Inject AC test current between the electrode and C2 using the earth tester
5. Measure the voltage between the electrode and P2
6. Earth resistance R = V / I (the meter does this calculation internally)

Common instruments: Kyoritsu 4105A, Megger DET4TC2, Fluke 1623-2. These inject a low-voltage AC signal at a non-power frequency (typically 128 Hz or 820 Hz) to avoid interference from stray DC or 50/60 Hz currents in the soil.

Safety note: Never conduct earth resistance tests with the electrode still connected to the earthed system. A disconnected earth means equipment is unprotected during testing -- keep the work area clear and reconnect immediately after testing.

Earthing System Types (TN, TT, IT)

The earthing system designation describes how the source neutral and exposed metalwork are earthed:

• TN-S: Separate neutral and protective earth conductors throughout. Most common in new industrial installations.
• TN-C-S (PME): Combined neutral/earth (PEN) from source, then separated at the consumer's incoming point. Standard UK domestic supply.
• TT: Source neutral earthed at the source, consumer metalwork earthed independently to a local electrode. RCD protection essential.
• IT: Source not earthed (or high-impedance earthed). Used in medical locations and some industrial processes for continuity of supply on first fault.

Create Your Own Earthing Diagram

Documenting an earthing installation is required for inspection and future maintenance. With CircuitDiagramMaker, you can:

• Draw plan views showing electrode locations, spacing, and trench routes
• Create cross-section diagrams of the earth pit construction layers
• Show the bonding connections between equipment frames, cable trays, and the main earthing terminal
• Label resistance values at each electrode from test records
• Export your earthing diagram as a PDF for the installation record

Create your own earthing diagram -- free

Key Takeaways

• Plate, pipe, and strip earthing all achieve the same goal -- a low-resistance path to earth -- using different electrode geometries suited to different site conditions.
• IS 3043 specifies GI plate at 600 × 600 × 6 mm and GI pipe at 38 mm bore × 2.5 m minimum for standard installations.
• Charcoal, salt, and coke fill around electrodes reduces contact resistance and retains moisture for long-term performance.
• Target earth resistance: below 1 ohm for substations, below 5 ohms for LV distribution, below 10 ohms for general equipment.
• Multiple electrodes in parallel reduce resistance -- space them at least the electrode length apart to minimize mutual shielding.
• Measure earth resistance using the fall-of-potential method with a dedicated earth tester before commissioning.
• The foundation earth electrode (rebar in concrete) is increasingly used as the primary electrode in modern buildings.

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Originally published at https://circuitdiagrammaker.app/blog/earthing-diagram-guide.