Mechanical Cable Lug Selection Guide: Conductor Material, Shape, Range, and Palm Dimensions

A mechanical lug can match the cable cross-section and still be unusable at the equipment. The usual causes are an unsupported conductor construction, a palm hole that does not fit the stud, a palm that is too wide for the terminal pad, or a barrel that interferes with phase barriers and cable bending space. This mechanical cable lug selection guide turns those interfaces into purchasing fields for switchgear, transformer, motor, and busbar terminations.

Start with the cable data sheet and the equipment terminal drawing. Then select from a verified mechanical cable lug range. Do not approve a lug from its headline cross-sectional range alone.

Use Five Checks in the Correct Order

1. Match Both Metal Interfaces

The first interface is conductor-to-barrel. The second is palm-to-equipment pad. Record the cable conductor material and the terminal pad or busbar material separately.

• For a copper conductor, use a lug whose data sheet explicitly approves the stated copper conductor construction.
• For an aluminum conductor, confirm that the body, contact preparation, inserts, and installation instructions are intended for aluminum.
• For an aluminum cable connected to copper equipment, request a supplier-approved transition arrangement. A plated surface should not be treated as automatic proof that every aluminum-to-copper interface is acceptable.
• If the project requires a dedicated transition component, review the available bimetal cable lug options, but do not substitute a compression lug for a specified mechanical lug without engineering approval.

A bimetal lug illustrates why the conductor-side and equipment-side materials must be specified separately.

2. State Shape and Conductor Construction

“240 mm² aluminum cable” is not a complete selection description. A 240 mm² round stranded conductor, compacted conductor, and sector conductor do not necessarily present the same geometry inside a lug. Solid and flexible conductors create additional differences in contact behavior.

Use the cable manufacturer’s designation and drawing to state:

• round or sector-shaped conductor;
• solid, stranded, compacted stranded, or flexible construction;
• nominal cross-section and, where applicable, AWG or kcmil size;
• actual conductor diameter or dimensional range;
• conductor class under the project-specified standard.

Do not assume a sector conductor may be rounded before insertion. Pre-rounding, inserts, centering rings, or other preparation must follow the selected lug’s instructions. Fine-stranded conductors also require explicit approval; a range tested for conventional power-cable conductors should not be extended to flexible cable by inference.

3. Read the Range by Model, Not by Product Family

A broad family range describes the catalogue, not one universal lug. CONWELL’s BLMT page lists the family from 25 to 630 mm², while individual models cover narrower bands such as 25–95, 35–150, 95–240, 120–300, 185–400, and 500–630 mm². The buyer must select the individual row that covers the actual conductor.

The listed range still needs confirmation for the conductor’s material and construction. Ask the supplier for the applicable selection table and installation instructions, rather than relying only on the marking shown in a product photograph.

CONWELL BLMT mechanical cable lug; the exact conductor range and palm-hole option are model-specific.

For low- and medium-voltage terminations, the shear-bolt mechanical lug option lists a high-strength aluminum-alloy body, aluminum-alloy bolts, tin-plated surface, and individual cross-section bands. CONWELL states that the family is intended for low- and medium-voltage cable terminations up to 35 kV. Project approval should still be based on the exact model documentation.

4. Convert the Equipment Drawing into Palm Dimensions

The palm is part of the electrical and mechanical interface. Obtain the switchgear, transformer, motor, or busbar drawing before releasing the purchase order.

Stud and hole

Record the stud diameter and the required clearance-hole diameter. A model suffix such as 13 or 17 may indicate a nominal palm-hole dimension, not an M13 or M17 stud. Verify the manufacturer’s dimension drawing and the equipment fastener. An oversized hole reduces seating area; an undersized hole creates site rework.

Hole pattern

Confirm whether the terminal pad requires one hole or two. For a two-hole interface, specify both hole diameter and center-to-center pitch. Also define the permitted orientation. Do not drill a second hole or enlarge a palm on site unless the equipment and lug manufacturers approve the change.

Palm width, thickness, and usable bearing area

Check that the palm sits fully on the equipment pad without contacting barriers or adjacent hardware. Palm width, thickness, edge distance, flatness, and available washer area affect fit. The selected bolt length must accommodate the terminal pad, lug palm, washers, locking arrangement, and nut engagement.

Overall envelope

Compare overall lug length, barrel diameter, palm offset, bolt-head access, and cable entry direction with the cubicle drawing. Maintain the equipment manufacturer’s phase-to-phase and phase-to-earth clearances. The cable should enter the barrel without forcing the termination or violating its minimum bend radius.

Application Decisions

Switchgear and busbars

Prioritize palm fit, phase-barrier clearance, tightening access, and cable routing. A narrow cubicle can reject an electrically suitable lug because the body or bolt head cannot be reached after the cable is positioned.

Transformer terminals

Verify the terminal pad material, stud arrangement, allowable cable direction, and any vibration or thermal-cycling requirements. If several parallel cables share one phase, confirm the permitted lug stacking arrangement with the transformer manufacturer.

Motors and industrial equipment

Check the terminal-box opening, palm width, creepage and clearance, cable gland position, and resistance to vibration. The installation should not transfer cable weight or bending force into the equipment terminal.

Where several cable constructions and field conditions must be covered, ask for a documented mechanical connection solution rather than selecting from photographs or a generic size chart.

Installation and Acceptance Records

The purchase specification should define the installation evidence needed at handover. For shear-head designs, use the bolt sequence, holding method, and any insert or centering component stated by the manufacturer. Do not add an unapproved torque value after the head has sheared.

• cable ID, phase, location, and equipment terminal reference;
• conductor material, construction, cross-section, and measured diameter when required;
• lug manufacturer, exact model, batch or traceability code;
• confirmation that the conductor was prepared according to the instructions;
• insert or centering-ring configuration, if applicable;
• bolt-tightening sequence and final shear-head condition;
• palm bolt size and final equipment-side torque;
• photographs before insulation, sealing, or cover installation;
• inspection result, installer identity, date, and calibrated-tool reference where required.

Mechanical Cable Lug RFQ Checklist

FAQ

Can I select a mechanical lug only by cable cross-section?

No. Cross-section is only one field. The exact model must also cover the conductor material, shape, construction, and class, while its palm and overall envelope must fit the equipment.

Does a range-taking lug fit every conductor within the marked range?

Only when the supplier’s table approves that conductor type. A range for round stranded aluminum cannot automatically be applied to sector, solid, compacted, copper, or fine-stranded conductors.

Is a 13 mm palm hole suitable for an M13 stud?

Do not read the hole dimension as a stud designation. Compare the actual hole diameter with the equipment stud and its specified clearance, washer, and bearing requirements.

What should be approved before bulk ordering?

Approve the exact lug model against the cable data sheet and equipment drawing. For a new interface, a sample fit check is useful before production quantities are released. Confirm the required test evidence and installation records at the same time.

Send Complete Interface Data for Selection

For a mechanical cable lug selection guide tied to your project, submit the cable data sheet, conductor construction, equipment terminal drawing, voltage and fault-duty requirements, quantity, required delivery date, and document list through CONWELL’s contact page. The supplier response should identify the exact model, approved conductor range, palm dimensions, installation method, and supporting documents so the lug can be checked before procurement and installation.