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:

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

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):

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):

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:

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:

Strip materials:

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:

Create Your Own Earthing Diagram

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Key Takeaways