technical of EARTHING PLATES & MATS
1. Ultimate Tensile Strength (UTS)
1. Copper Plate:
I. UTS ~ 210–250 MPa
2. MS GI Plate (hot rolled):
I. UTS ~ 370–490 MPa (depends on grade, e.g., IS 2062 Fe410/Fe540)
3. Earthing Mats (made from MS flats/rods):
I. Similar range, depending on cross-sectional size
4. Plates must withstand ground pressure, thermal stress during fault, and handling loads during installation.
2. Working Load / Safe Working Load (SWL)
1. Normally taken as 1/3 of UTS for safety:
I. For GI plate with 490 MPa UTS, SWL = 160–170 MPa equivalent force
II. Plates/mats laid flat in pits must not deform under soil compaction or equipment load
2. Mats designed for load-bearing of ~1–2 tons/m² if laid under structures.
3. Conductor Diameter Compatibility
1.Plates and mats have pre-drilled holes or welded lugs for direct bolting or welding of conductors.
2. Compatible with:
I. Copper strips (25 mm × 3 mm, 50 mm × 6 mm)
II. GI strips (25 mm × 3 mm to 50 mm × 10 mm)
III. Conductors of 6 mm to 50 mm width,
or 6–12 mm rods
3. Accommodate exothermic weld, brazing, or bolted connection.
4. Slip Strength:
1. Applicable in bolted joints between plate/mat and earthing conductors.
2. Joints tested to resist axial slip >5–10 kN, depending on bolt torque and surface treatment.
3. Plates should not allow loosening of clamps/bolts under vibration or surge heating.
5. Temperature Withstanding Capacity:
1. Designed to withstand:
I. Continuous earth temperature: –40°C to +85°C
II. Short-term fault current heat: up to 300–400°C (Copper), 250–300°C (GI)
2. Thermal expansion and conductivity critical for safely dispersing fault and lightning surges.
6. Corrosion Resistance:
1. Copper plates: Excellent corrosion resistance; service life > 40 years
2. GI plates: Hot-dip galvanized to ≥ 80–100 μm zinc coating (as per IS 2629/ASTM A123)
3. Resistance tested in:
I. Saline, acidic, and alkaline soils
II. High-moisture environments (pits, marshy areas)
7. Impact & Fatigue Strength:
1. Withstand:
I. Impact from falling tools or trench collapse during backfilling
II. Vibration from nearby equipment or traffic
III. Thermal fatigue from repeated fault surges
2. GI plates have high ductility; copper offers better resilience under electrical loading.
8. Mechanical Endurance:
1. Service life:
I. Copper: ≥ 40–50 years
II. GI: ≥ 15–25 years (in moderately corrosive soil)
2. Mats tested for:
I. Thermal aging,
II. Mechanical loading, and
III. Corrosion cycles
9. Design Safety Factors:
1. Mechanical Safety Factor: ≥ 2.5–3.0
2. Electrical Design Factor:
I. Adequate surface area to dissipate current without exceeding allowable ground potential rise (GPR)
Top 5 Quality Assurance
1. Material & Metallurgical Testing
a. Copper plate:
I. Purity ≥ 99.9% tested by spectrometry
II. Conductivity ≥ 97% IACS
b. GI plate:
I. Zinc coating thickness (≥ 80 µm) checked using DFT meter
II. Tensile, hardness, and bend tests as per IS 2062/IS 2633
2. Dimensional & Structural Inspection
a. Size accuracy within ±1 mm tolerance
b. Surface finish checked for:
I. Cracks
II. Warping
III. Pitting or galvanizing peel-off
c. Weld joint inspection (for mats): Visual + NDT (DPT/MPT)
3. Electrical Resistance & Thermal Test
a. Joint resistance ≤ 1 milliohm
b. Short-time current test (simulated fault):
I. Plate should remain structurally and electrically intact after surge
c. Infrared thermography may be used for hotspot detection in lab test
4. Corrosion & Environmental Testing
a. Salt spray test (ASTM B117, ≥ 500–1000 hrs)
b. Soil burial test simulation for accelerated corrosion aging
c. pH exposure (acidic or alkaline resistance)
5. Marking, Traceability & Compliance Documents
a. Each item marked/stamped with:
I. Manufacturer logo
II. Material grade (e.g., Cu 99.9%, GI HDG)
III. Size and batch no.
b. Supplied with:
I. Routine test reports
II. Type test certificates (if specified)
III. Third-party inspection certificates
IV. GTP & IS 3043 compliance declaration