Bundle blocks are used on high-capacity, long-distance, high-voltage transmission-line construction projects. These are projects that are planned many months in advance of construction in order to take into consideration the distance and terrain of the route, the voltages, and the capacity of the line. All of these factors (and others) affect the type, size, and number of conductors used and how they will be configured and installed. All of these factors further affect the configuration of the blocks that will be used. Since almost all projects are a bit different, bundle blocks are usually custom-configured and engineered specifically for each project.

Consequently, bundle blocks do not lend themselves to being configured from a set of tables in a catalog or on a website. Rather, bundle blocks must be configured in consultation with Sherman & Reilly. As preparation for that consultation, it is useful to understand the steps involved, which are to determine:

1. Sheave size.
2. Sheave lining, if any.
3. Number of conductors.
4. Separate pulling-line sheave, if any.
5. Frame type & design.
6. Fittings & hanging hardware.
7. Attachments.

Sheave size is largely a function of the size of the conductor being strung and of span length and terrain over which the conductor will be installed. Sheave lining is largely a function of the type of conductor being used and/or requirements from the conductor manufacturer.

Whether a separate sheave for the pulling line is needed is largely driven by the conductor manufacturer having a requirement for a separate sheave, so as to avoid contamination and/or damage to the conductor caused by damage done to, or dirt/debris left on, the sheave by a steel pilling line.

Frame size/type and fittings/hanging hardware are almost entirely a function of sheave size, the manner by which the block will be suspended, by conductor spacing, and the manner by which the conductors will be affixed (“clipped in”) to the insulators. The addition of an aluminum center-drum may be required to achieve the desired conductor spacing. Depending on configuration, the pulling-line groove of that center-drum may be either a groove made of steel inserts or a machined groove lined with urethane.

Attachments are a function of how the conductor will be installed and grounded.

The three design variations (symmetrical, slim-line, and offset) allow for matching the block configuration to the number of conductors, to whether there is a separate pulling-line sheave, and to the separation between conductors when attached to the insulators on the tower.

The symmetrical design accommodates two, three, four, and six-conductor configurations. The sheaves are equidistant from each other regardless of the number of conductors. Usually, these blocks are configured for 18″ outside centers. Depending on the number of conductors and the their configuration, these blocks may have a center-drum with a center groove for the pulling line to pass through. This center groove can be either high-carbon steel inserts or urethane lined. If the center-drum is a one-piece design, then the groove is lined with urethane. If the center-drum is a two-piece bolt-on design, then the center groove is made of steel inserts.

The slim-line design is limited to three-sheave blocks that can be used for stringing two or three conductors that are clipped in on closer centers. This design is ideal for use where minimum weight and cost are prime factors.

The offset design makes use of special geometry to achieve a balance of two conductors with one. Such a balanced design facilitates the simultaneous stringing of three conductors while having a separate sheave for the pulling line. Therefore, this design greatly reduces the risk of damage to any conductor or conductor sheave caused by the pulling line, while minimizing twisting and misalignment caused by imbalance. This design is offered in a 28″ sheave size, only. (This design block may also be used to string two conductors on 18” centers by simply disassembling the block frame on one side and rotating the inter-flange sheave 180º to create a two-conductor configuration.)