technical of GROUNDING CONDUCTORS
1. Ultimate Tensile Strength (UTS)
1. UTS depends on material and cross-sectional area:
I. Copper (annealed): ~200–250 MPa
II. Copper (hard-drawn): ~300–400 MPa
III. GI (hot-dip galvanized steel): ~500–700 MPa
IV. Copper-clad steel (CCS): ~600–900 MPa
b. Example: A 70 mm² copper conductor has a UTS of approx. 7–9 kN
2. Working Load / Safe Working Load (SWL)
1. SWL is usually taken as 30–40% of UTS, accounting for dynamic loads:
I. Example: For a CCS conductor with UTS of 800 MPa, SWL = 240–320 MPa equivalent force
2. Ensures conductor doesn’t fail under soil movement, vibration, or clamping stress
3. Conductor Diameter Compatibility
1. Grounding conductors come in standard sizes:
I. Copper: 16 mm² to 240 mm² (typically 25 mm², 50 mm², 70 mm²)
II. GI Strip: 25x3 mm, 50x6 mm, etc.
III. Compatible with grounding clamps, rods, and terminals having hole/slot sizes of 6 mm to 16 mm
2. Must match earthing lugs, clamps, or exothermic weld molds
4. Slip Strength:
1. Not directly applicable since conductors don’t “grip” the cross arm.
2. However, insulators and hardware bolted on the cross arm must not slip under load.
3. Bolt slippage prevention through:
I. Proper tightening (torque 35–50 Nm)
II. Spring washers
III. Galvanized threaded inserts
5. Temperature Withstanding Capacity:
1. Cross arms are exposed to direct sun, rain, ice, and thermal cycling.
2. Steel cross arms:
I. Withstand up to 400°C (no mechanical loss until ~250°C)
3. FRP cross arms:
I. Withstand up to 150°C continuous, short-term peaks up to 200°C
4. Working Range:
I. -40°C to +120°C (normal ambient)
II. No deformation or cracking in temperature cycling
6. Corrosion Resistance:
1. Bare Copper: Excellent corrosion resistance, even in acidic or saline soil
2. Tinned Copper: Enhanced for marine/industrial zones
3. GI: Moderate corrosion resistance; may degrade in highly acidic/alkaline soils
4. Copper-Clad Steel (CCS): Combines strength of steel and corrosion resistance of copper
7. Impact & Fatigue Strength:
1. Stranded copper and CCS offer high flexibility—resist mechanical vibration, bending, and handling stress
2. GI strips may be more brittle and susceptible to fatigue under cyclic loading
3. Fatigue tested under simulated vibration and temperature cycling
8. Mechanical Endurance:
1. Expected service life:
I. Copper: ≥ 40 years
II. CCS: ≥ 30–40 years
III. GI: ~10–15 years (depending on environment)
2. Tested by long-term fault current simulation and underground burial endurance tests
9. Design Safety Factors:
1. Designed with electrical and mechanical safety factors of ≥2.5 to 3.0
2. Fault current handling capability:
a. 25 mm² copper can handle ~11 kA for 1 second
b. 50 mm² copper: ~21 kA for 1 second
c. GI or CCS may need higher cross-sections for similar performance
Top 5 Quality Assurance
1. Mechanical & Electrical Type Testing
a. Tensile test to confirm UTS
b. Current carrying capacity test (e.g., withstand 40–50 kA fault for 1 second)
c. Resistance test (conductor resistance at 20°C)
d. As per IS 3043, IEC 62561-2, BS EN 13601
2. Conductor Purity & Composition Testing
a. Copper: Must be >99.9% purity, verified by spectrometry
b. GI: Coating weight and thickness tested per IS 2629 / ASTM A123
c. CCS: Bonding test to ensure uniform copper cladding and no delamination
3. Corrosion & Soil Exposure Simulation
a. Salt spray test for 500–1000 hrs (ASTM B117)
b. Soil burial test to evaluate long-term corrosion impact in acidic or saline soil
c. Visual inspection post-exposure
4. Dimensional & Visual Inspection
a. Check for:
I. Conductor cross-sectional area
II. Uniform strand lay and compactness
III. Surface finish (no cracks, oxidation, burrs, or flattening)
b. Verify insulation (if PVC sheathed)
5. Marking, Traceability & Documentation
a. Conductors tagged or printed with:
I. Manufacturer name
II. Size and type (e.g., Cu 70 mm², GI 25x6 mm)
III. Batch number
b. Supplied with:
I. Routine test reports
II. Type test certificates
III. GTP (Guaranteed Technical Particulars)
IV. ISO 9001, 14001 compliance