technical of T-CLAMPS
1. Ultimate Tensile Strength (UTS)
1. Clamp Body (Aluminum alloy):
I. UTS: ~150–250 MPa, depending on alloy and casting integrity
2. Bolts (HDG steel / SS 304):
I. UTS: 400–800 MPa, depending on grade (e.g., Class 8.8 or SS304)
2. Working Load / Safe Working Load (SWL)
1. SWL refers to:
I. Mechanical grip on both main and tap conductors
II. Clamp integrity during dynamic loads (wind-induced vibration, weight of tap conductor)
2. SWL typically 1/3 of UTS, i.e.
I. For aluminum body: 50–80 MPa equivalent safe stress
II. Overall mechanical grip: 4–6 kN for small clamps, up to 10–15 kN for large clamps
3. Conductor Diameter Compatibility
1. T-clamps are available for a wide range of conductor sizes:
I. Main conductor: 14 mm – 40 mm (ACSR/AAAC)
II. Tap conductor: 6 mm – 25 mm
2. Most designs include grooved and contoured seats for exact fit to the conductor strand size and shape
4. Slip Strength:
1. Important to maintain a firm electrical and mechanical grip under thermal cycling and vibration
2. Minimum slip strength: >5–8 kN (varies with clamp size and torque)
3. Achieved via:
I. Serrated/grooved contact surfaces
II. Proper bolt torque (typically 30–60 Nm)
III. Multiple bolt designs for uniform pressure
5. Temperature Withstanding Capacity:
1. Operating range: –40°C to +85°C
2. Fault or surge condition: Can withstand up to 250°C – 300°C for short durations
3. Thermal expansion of aluminum is accounted for in design to prevent loosening
6. Corrosion Resistance:
1. Aluminum body: Naturally corrosion-resistant; may be anodized for improved protection
2. Bolts/Nuts:
I. HDG Steel: Zinc coating ≥ 80 µm (IS 2629/ASTM A153)
II. SS 304/316: Excellent resistance in coastal or polluted environments
3. Bimetallic T-clamps use copper inserts or inhibitors to prevent galvanic corrosion
7. Impact & Fatigue Strength:
1. Withstand:
I. Vibration from conductor galloping or wind
II. Minor mechanical shocks during installation
III. Thermal fatigue from load cycling
2. Life cycle tested for 10,000+ vibration or expansion/contraction cycles
8. Mechanical Endurance:
1. Designed for a service life of 30–40 years under normal field conditions
2. Withstands:
I. Daily thermal cycles
II. Conductor pull
III. Weight of tap conductor
3. Long-term clamping pressure retention critical
9. Design Safety Factors:
1. Mechanical factor of safety: ≥ 2.5–3.0
2. Electrical safety includes:
I. Sustained low contact resistance
II. Heat dissipation without causing hot spots
III. Fault current passage without degradation
Top 5 Quality Assurance
1. Mechanical & Electrical Type Testing (per IS 5561 / IEC 61284)
a. Tensile test for:
I. Clamp body
II. Slip strength
b. Electrical contact resistance test (target: ≤ 100 micro-ohms)
c. Short circuit current withstand test (e.g., 25–40 kA for 1 second)
2. Material Testing & Compliance
a. Aluminum casting verified for:
I. Composition (ASTM B108 / IS 617)
II. UTS, elongation, porosity
b. Bolts/nuts tested for:
I. Galvanizing thickness (DFT meter)
II. Tensile grade (proof load)
III. Thread conformity (go/no-go gauge)
3. Dimensional & Visual Inspection
a. Dimensions checked using gauges or vernier calipers
b. Visual inspection for:
I. Cracks, burrs, surface porosity, casting defects
II. Correct bolt hole positioning and parallelism
c. Surface finish verified for coating integrity
4. Corrosion & Environmental Testing
a. Salt spray test (ASTM B117): ≥ 500–1000 hours
b. Optional:
I. Humidity chamber testing
II. Soil burial simulation for bimetallic clamps
c. Verifies long-term resistance to rust and electrolytic degradation
5. Marking, Traceability & Compliance Documents
a. Each clamp marked with:
I. Manufacturer name/logo
II. Conductor size/type
III. Batch number
b. Supplied with:
I. GTP (Guaranteed Technical Particulars)
II. Routine test certificate
III. Type test reports (optional: CPRI/ERDA certified)
IV. ISO 9001:2015 compliance documentation