NLD Series Bolt-Type Strain Clamp for Overhead Conductors
The NLD series bolt-type strain clamp is a mechanical line fitting used to secure bare overhead conductors at tension poles, angle structures and line dead ends. The conductor is placed inside the curved clamp body and retained by pressure plates and U-bolts. The attachment eye connects the clamp to a tension insulator string, clevis fitting or other compatible pole-line hardware.
The bolted construction allows the clamp to be installed without hydraulic compression equipment. Different NLD models are available according to conductor material, conductor outside diameter, required mechanical strength, number of U-bolts and connection dimensions.
Important: The correct clamp must be selected using the actual conductor type, construction and outside diameter. The model marking alone must not be used as a substitute for an approved dimensional drawing and mechanical test report.
Key Features
- Bolted mechanical clamping structure
- Designed for conductor dead-end and tension applications
- U-bolts provide adjustable clamping pressure
- Integrated attachment eye for connection to an insulator string
- No hydraulic compression equipment required for installation
- Hot-dip galvanized ferrous construction available for outdoor service
- Multiple models for different conductor diameters and mechanical loads
- Custom conductor range, dimensions, marking and packaging available
Typical Technical Specifications
| Product Type | Bolt-Type Strain Clamp / Tension Clamp / Dead-End Clamp |
|---|---|
| Series | NLD Series |
| Representative Models | NLD-1, NLD-2, NLD-3 and NLD-4 |
| Clamping Method | Mechanical clamping with U-bolts |
| Main Components | Clamp body, pressure plate, U-bolts, nuts, washers and attachment eye |
| Body Material | Malleable cast iron, ductile iron or approved project-specific material |
| U-Bolt and Hardware Material | Carbon steel |
| Surface Finish | Hot-dip galvanized, subject to the approved specification |
| Compatible Conductors | Bare AAC, AAAC or ACSR conductor when approved for the selected model |
| Connection | Attachment eye connected to an insulator string or compatible fitting |
| Application | Tension pole, angle pole and overhead-line dead-end structure |
| Mechanical Rating | Specified by model and verified by the applicable test report |
| Customization | Conductor range, U-bolt quantity, dimensions, material, coating, marking and packaging |
Model availability and technical data must be confirmed using the approved factory drawing. Do not publish conductor ranges or failure loads without verified product data.
Structure and Working Principle
The conductor is positioned in the curved groove of the clamp body. U-bolts and pressure plates apply mechanical pressure to retain the conductor and transfer longitudinal line tension to the clamp body. The load is then transferred through the attachment eye to the insulator string and supporting structure.
Clamping force must be distributed evenly. Incorrect conductor diameter, uneven tightening or excessive torque may deform the conductor, damage individual strands or reduce the mechanical performance of the termination.
Typical Applications
- Overhead distribution-line dead ends
- Tension poles and angle poles
- Bare conductor termination
- Connection to tension insulator strings
- Utility-grid construction and refurbishment
- Rural electrification projects
- Industrial overhead power networks
Conductor Compatibility
NLD series clamps may be manufactured for bare aluminum conductors, aluminum-alloy conductors and aluminum conductors steel reinforced. Compatibility depends on the clamp groove, conductor outside diameter, conductor construction and required holding strength.
This clamp must not automatically be used on covered or fully insulated conductors. Direct metal clamping may damage the insulation unless the complete clamp system has been specifically designed and approved for that cable.
Installation Guidance
- Confirm the conductor type, construction and outside diameter.
- Select the corresponding clamp model from the approved selection table.
- Inspect the body, groove, U-bolts, nuts and attachment eye for damage.
- Clean the conductor surface and clamp groove where required.
- Position the conductor correctly inside the clamp body.
- Install the pressure plates and U-bolts in their specified positions.
- Tighten the nuts gradually and alternately to distribute pressure evenly.
- Apply the manufacturer-specified tightening torque.
- Connect the attachment eye to the approved insulator-string fitting.
- Perform a final inspection for loose hardware, conductor damage and incorrect alignment.
Installation must be performed by qualified line personnel according to the approved construction drawing and utility safety procedure.
Quality Inspection
- Raw-material verification
- Dimensional and conductor-groove inspection
- U-bolt thread and nut-fit inspection
- Clamp-body visual inspection
- Hot-dip galvanized coating inspection
- Mechanical holding-strength test when specified
- Rated failure-load test according to the agreed standard
- Marking, quantity and packaging inspection
Reference Standards
- DL/T 757-2021 – Strain Clamps
- IEC 61284:1997 – Overhead Lines: Requirements and Tests for Fittings
- ISO 1461:2022 – Hot-Dip Galvanized Coatings on Fabricated Iron and Steel Articles
- Applicable utility drawings and project specifications
Reference to a standard does not constitute certification. Compliance must be supported by inspection or test documentation for the exact clamp model.
Ordering Information
Please provide the following information when requesting a quotation:
- Required NLD model
- Conductor material and construction
- Conductor outside diameter
- Required mechanical or failure load
- Number and dimensions of U-bolts
- Attachment-eye dimensions
- Body and hardware material
- Required zinc-coating specification
- Applicable standard and required test reports
- Order quantity, marking and packaging
Frequently Asked Questions
What is an NLD strain clamp used for?
It is used to mechanically terminate a bare overhead conductor at a tension pole, angle pole or line dead-end structure and transfer the conductor tension to an insulator string.
How is the correct NLD model selected?
The model must be selected according to conductor type, conductor outside diameter, required holding strength, U-bolt arrangement and connection dimensions.
Does the clamp require hydraulic compression?
No. The conductor is retained by pressure plates and U-bolts. Correct tightening torque and installation sequence are still required.
Can it be used with insulated conductors?
Not automatically. The illustrated clamp is intended primarily for bare conductors. A specifically approved clamp system should be used for covered or insulated conductors.
Is the clamp electrically rated by voltage?
The clamp is principally selected by conductor and mechanical requirements rather than by voltage alone. Its use in a particular voltage system must be confirmed through the complete overhead-line design.
