Material Handling with Digger Derricks and Aerial Devices

Terex Digger DerrickToday’s digger derricks and aerial devices are built to be versatile pieces of equipment for utility workers, whether it’s digging holes, lifting and setting poles, turning in screw anchors, putting linemen in the air, or setting transformers. However, that versatility further underscores the need for specific work practices to be properly managed.

This article looks at two common tasks: lifting poles with digger derricks and using the aerial device’s jib for handling transformers. Done improperly, these tasks can cause equipment damage or personnel injuries.

Best practices for pulling poles

Manufacturers prohibit using a digger derrick to rock a pole loose or using the load line to forcibly remove the pole. These practices apply a side load and can impose unknown loads and forces that key components were not designed to withstand. The pedestal, turntable, boom, cylinders, pole guides, subframe, outriggers and winch are all vulnerable and potentially expensive to repair or replace if damaged. Cracks, rust, loose paint, loose fasteners, deformation or other damage to the boom, pedestal, or subframe are signs that side loads, shock loading, or overloading has occurred.

Instead of using the boom’s brute force, a pole puller provides strategic force for loosening frozen or embedded poles. In extreme cases, it may be necessary to dig one or more holes with the digger derrick auger alongside the pole to loosen the soil to assist the pole puller. Once the pole is loose, then the lift cylinders can be used to lift the freely suspended pole while using the pole guides to maintain control only, not lift.

Before selecting the digger derrick and positioning for the job, certain information is key in maintaining a controlled lift. If you don’t know the weight of the pole, use readily available charts that provide approximate weight based on the pole’s material and length. Also take into consideration if the pole is wet or wrapped, plus anything that may be attached to the pole such as cross members, transformers, insulators, and wire. Consult unit specific load charts on the digger derrick to make sure it has the capacity needed to lift the load through the complete path that the load will travel—beginning with extraction point and ending with the location of the final placement.

The actual lifting should only be done within the lift cylinder capacity, the load chart and the number of parts of line – do not use the pole guides to lift the pole. The pole guide should only be used to help control the pole once it is vertical.  The rigging attaching the pole to the load line must be above the balance point of the pole to keep the butt end heavy and down.

Lifting transformers with jibs

Before lifting and placing transformers with a jib, first consider whether the tasks are construction or maintenance work on distribution or transmission lines. This can affect which industry standards apply. Then before dispatching to the job, workers should know how the lines are situated relative to where the vehicle can be located.

While many aerial devices sold to the utility industry are equipped with jibs, all jibs are not the same. The user should evaluate the type of work when choosing the equipment.

Like with digger derricks, the weight of the load will determine the aerial device and the jib capacity needed. Transformers vary in size, weight, and shape. A 3kVA transformer weighs just 50 pounds, while higher capacity transformers can weigh more than 1,000 pounds. New transformers will include the weight on the unit ID tag, but when removing old transformers, the weight of the load may be unknown. It is a good idea to refer to the brand name, model, and type of core to identify the weight. This information is usually available from the transformer manufacturer.

The load chart provides the maximum capacity of the aerial device based on the boom and jib or load line positions. These capacities must be followed. If exceeded, the stability or strength of the unit is compromised. Likewise, operators must know the load weight and the boom configurations required through entire load travel path. Note the maximum winch lifting capacity may greatly exceed the capacity at your working position and must never be used as an indication of allowable load. The load chart provides capacities at various boom angles, load radii or jib extensions. 

As the load is positioned farther from the boom tip the capacity, in most cases, is reduced. Most aerials have the same capacity over the side as well as the back.  If there are restrictions the information will be provided on the load chart or other labels at the operator station. 

Terex Utilities designed its Load Alert system to help operators know if the boom condition is near capacity. It monitors and analyzes the truck’s jib and basket capacity and provides visible and audible alarms when an overload has been detected to aid users. A monitor display will read ‘overload’ when one occurs, and the background will turn red. The display also shows the actual load amount and will warn when the operator is approaching maximum capacity.

When lifting with a jib, it is important to follow the manufacturers limitation on set up if on a slope, some must be level, or you may cause the unit to tip or roll over. This is especially true if the truck is setup across a slope and is lifting from the side.

Finally, Terex Utilities recommends always using an insulating section or link when working with a jib while lifting energized lines. The conductor lifter or insulating link must be treated as a hot stick. The clear span distance of the insulating tool depends on the voltage. Users should follow OSHA 1926.950 to maintain minimum clear insulation distances required.

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