Tandem Sheave Stringing Block for Twin Bundle Conductor Pulls
Two sub-conductors pulled on two separate blocks never keep their spacing. One sheave runs ahead, the spacing opens or closes, and the crew spends the afternoon chasing it. A tandem block fixes the spacing in the frame itself: two sheaves on one body, 25KN rated, for LGJ 300 to 500 twin bundle work, in aluminium at 11kg or nylon at 9.5kg. The pair runs at the spacing the frame was built for, on one hanger, with each sheave on its own sealed bearing.
Model Data
| Item No. |
Model |
Suitable Conductor |
Rated Load (kN) |
Weight (kg) |
Sheave |
| 10211 |
SHR-2.5 |
LGJ 300-500 |
25 |
11 |
Aluminium |
| 10212 |
SHRN-2.5 |
LGJ 300-500 |
25 |
9.5 |
Nylon |
25KN is the block rating. Each groove carries its share of the pull, and where the two sub-conductors are tensioned to different values the split follows the tension, so the per-groove share is confirmed against the tensioner setting at order stage.
Why a Tandem Block Beats Two Single Blocks
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Spacing is a frame dimension, not a rigging decision: the two grooves sit on a fixed centre distance, so the bundle spacing at the block matches the design spacing without measuring at every structure.
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One hanger, one lift: half the hanging hardware, half the climbing, and no risk of two blocks drifting apart on the arm under load.
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Equal wrap and equal friction: both conductors pass over the same diameter sheave with the same arc of contact, which is what keeps the two sags matching after the pull.
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Separate bearings per sheave: each wheel turns independently, so a slight tension difference does not drag one conductor over a stationary sheave and scuff it.
Spacing, Sag and Tension
The tandem frame sets the spacing; the tensioner sets the sag. Both matter. If the spacing at the block is right but the two conductors are pulled at different tensions, the sag will differ and the spacers will not sit square. Pull both sub-conductors from the same tensioner through the tandem block so the tension is inherently common, keep the first block at least ten times the sheave diameter behind the machine, and check the bundle spacing at the first three structures before committing to the rest of the section.
Rigging Notes
Hang the block so the frame is square to the conductor line; a twisted hanger loads one sheave more than the other and wears the groove unevenly. Confirm that both sheaves clear the crossarm and the insulator string through the full sag swing and, on angle structures, that neither conductor can touch the frame as the bundle comes round. Do not use the block as a running-out block or as an anchor.
Sheave Material and Service
Nylon for aluminium and coated conductor, aluminium where the groove has to survive repeated abrasion or steel rope. Both models share the frame and hanger, so a depot can standardise on one frame with two sheave options. Sheaves, bearings and pins are service parts; a scored groove means a sheave swap, not a new block.
Packing and Supply
Packed in plywood cases with sheaves protected from impact. Stock models ship in 3 to 7 days, monthly capacity around 3000 pieces, minimum order 1 piece, OEM marking and packing marks to the buyer drawing.
Frequently Asked Questions
Can the centre distance be made to our bundle spacing? Yes, the frame is built to the required spacing on order.
Is a four sheave version available? Quadrant and four sheave blocks are a separate product line for larger bundles.
Which model for LGJ 400 twin bundle? Either; nylon for conductor protection, aluminium for longer groove life.
Product Tags:
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25KN Tandem Sheave Stringing Block for Twin Bundle Spacing Control with Aluminium or MC Nylon Sheave Images
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