When pulling cable underground, an assortment of highly specific tools are needed in order to properly and efficiently feed cable into an existing duct. Below the manhole, a combination of sheaves, shackles, and jam skids are needed to effectively get the job done. In this blog, we’ll be explaining the necessary tools for underground cable placement, and providing a few examples of how they fit together.

Sheaves 

Cable Sheaves are used to guide underground cable as it’s passed from aboveground, into the manhole, and eventually into the conduit. A shackle hung with the eye end and chained to the wall behind it, the pulling frame as pictured above, or a jamb skid are necessary for holding cable sheaves steady as cable passes through them.

When used for pulling cable with a winch, the sheaves can be subjected to large amounts of force, meaning sheaves should be properly inspected prior to use.

GMP produces sheaves made from high-strength aluminum alloy, making them lightweight, durable, and long lasting. GMP sheaves have self-lubricating bushings that reduce the amount of maintenance and extend their overall life.

Our sheaves come in 3in. (8cm), 4in. (10cm), and 5in (13cm) sizes.

It’s important to note that many competitors use sheave pins that are not interchangeable.

The sheaves sized for a 1 5/16″ diameter sheave pin, are normally used with the GMP cable sheave shackle, a pulling frame, or a jamb skid. The sheave pin is supplied with the cable sheave shackle, pulling frame, or jamb skid.

The sheaves sized for a 1 1/4″ diameter pin are designed as direct replacements for other manufacturers’ sheaves. These sheaves will not work with the GMP cable sheave shackle, pulling frame or jam skid — so please order carefully.

 

Shackles

 The cable sheave shackle is used to support a cable sheave or quadrant block in place at a manhole equipped with pulling irons. GMP-produced shackles contain a two-part clevis made of high strength structural steel, and have two sets of sheave pin holes with 1 3/8 in. (35mm) dia. for accommodating either a cable sheave or quadrant block. The load half has a forged steel hook that easily attaches to the pulling irons in the manhole with a standard 1/2 in. (12mm) x 6 ft. (1.8 m) construction chain (GMP part number 63541). The support half has a shoulder eyebolt so you can tie it off to a support rope over the manhole.

GMP shackles will accommodate any 11 in., 20 in. or 26 1/2 in. cable sheave with a 1 3/8 in. hole size for 3 in., 4 in. or 5 in. cable. The shackles come in three widths, 3 in., 4 in. or 5 in., to accommodate the cable. Each individual shackle includes a 1 5/16 in. dia. sheave pin and can withstand working loads up to 10,000 lbs (4535kg).

Each shackle includes an OSHA mandated Safety Latch.

 

Jamb Skids

The Jamb skid is an alternative to using a shackle or pulling frame for rigging sheaves in place for underground cable pulling operations. Jamb skids are especially useful in manholes that do not have pulling-in irons. The term jamb skid comes from the two parallel vertical struts, like a door jamb, with an opening in between for mounting the sheave. The upper section of the jamb skid swivels for easier placement, giving it 360 degrees positioning capabilities inside the manhole. When the Jamb Skid is secured into position by depressing the over-center, locking foot pedal, it’s used as a stiff leg for the sheave, giving it sturdy and consistent pulling capabilities.

GMP-produced Jamb Skids are lightweight and corrosion resistant because they are constructed primarily of aluminum. Our Jamb Skids come in 3 different sizes depending on the specific measurements of a manhole. Once you have the base piece, extension pieces are also available for purchase.

Each jamb skid includes (2) 1-5/16 in. (33 mm) diameter locking pins (71717) to lock in the height and secure the sheave or quadrant block. Our jamb skids accept all GMP sheaves and quadrant blocks with widths up to 7 in. (178 mm)

 With fast moving cable, durable and effective equipment is necessary to have a safe and efficient day in the manhole. Since 1936, General Machine Products has been a leader in supplying the telecom industry. Visit us today at gmptools.com or call us at 215-357-5500 to learn more about underground equipment.