Knowing bucket capacity and understanding how to read a jib load chart are two critical elements of aerial device operation. While both tasks are fairly straightforward, it is crucial to stay within the allowable capacity of the unit. The platform capacity and material-handling capacity provided by the manufacturer are not recommendations – they are absolute maximum capacities that ensure the machine is not overloaded. Overloading equipment can result in overturning or boom failure. Equipment damage also may occur, resulting in costly repairs and a shortened usable life for the aerial device.
A fully equipped lineworker with PPE plus tools and materials for typical line maintenance can quickly add up to 700 pounds or more for distribution work, and upward of 1,000 pounds for transmission work. Bucket capacity is identified on the ID plate and inside of the basket on most aerial devices. In addition, be aware of dual-rated buckets with different capacities based on configuration and use as a material handler; these types of buckets are available from some manufacturers. Before climbing in, lineworkers should verify that their weight – in addition to the platform liner, if used, and all of their tools and equipment – doesn’t exceed the bucket’s capacity.
“Don’t forget to account for boots, harness, tools and any components you may add to the bucket once you are elevated,” said Kyle Wiesner, technical sales for Terex Utilities. “Tools such as phase lifters, crimpers, hydraulic drills or chainsaws all add up. Weight of personal clothing can change with the weather, so don’t forget to recalculate come winter. If a component is in the bucket while work is being performed, that weight needs to be factored in as well.”
If it is not equipped with a material-handling feature from the manufacturer, the aerial device must not be used to lift material with the platform or boom. The platform is not intended to handle material – only tools and equipment the operator can carry and that remain within the platform capacity.
Further, if gear is not labeled with its weight, lineworkers shouldn’t guess. Instead, use a small, portable scale to verify total weight before loading the bucket. Once you have weighed a tool or piece of gear that you use often, mark it with a small tag or permanent marker so you will have a record of the weight for next time.
Proper Jib Use
Proper jib use requires an understanding of how to read a load chart, plus knowing the upper boom angle, jib angle and load radius as specified on the load chart. Maximum permissible load on the jib varies depending on the boom and jib configuration. It’s necessary to verify the setup before a load is lifted.
While different bucket, boom or power-line positions dictate at what angle the jib is able to be used, the upper boom angle must be verified by looking at the angle indicator located on the boom. In addition, some jibs extend, which will increase the radius of the load, thereby decreasing capacity. A trial run with the boom and jib positioned as needed will provide the information necessary to confirm jib capacity. “It’s a good idea to keep a measuring tape handy to verify load radius,” Wiesner said.
The next step is to confirm that the weight of the object to be lifted is less than the maximum jib load for any configuration, from picking the load to placing the load. Load charts typically are located on the dash plate or boom tip, visible to the operator.
If it’s determined that the current equipment would overload the bucket or jib for the task to be performed, figure out what rated capacity would better meet the application. Then, if possible, use several machines – such as a digger derrick with the aerial – to aid in accomplishing the task, or purchase or rent the proper equipment. In any case, always encourage proper operator behavior and treatment of the equipment in order to keep employees safe.
Technology Can Help Change Behavior
While understanding these principles is basic for journeymen, what if there was an operator aid that could assist lineworkers with these tasks? Crane manufacturers and some non-insulated aerial manufacturers have applied sophisticated load-moment indicators to computer monitoring systems for years, which provide feedback to operators regarding load weight and capacities. More recently, self-propelled aerial lifts have been designed with active working range monitors of platform movement. Currently, certain standards – EN280 for Europe and ANSI A92.20 for some equipment in the U.S. – require aerial work platforms to monitor the weight in the platform and disable functionality if the load being detected is above platform capacity.
Dynamometers have been and continue to be available to aid equipment operators by giving them the ability to measure, not estimate, the load being lifted. The display on the dynamometer attached to the hook gives the load’s weight. Recently, load-measuring devices have been developed that work on insulated aerial devices in proximity to electrical fields created by power lines. The battery-operated radio devices provide a display near the operator that shows the weight of the load on the load line.
And rather than reinvent the wheel, Terex Utilities has collaborated with customers to create an operator aid that helps to inform lineworkers of a potential overload situation. The Terex Load Alert system consists of wireless sensors that measure boom angle, jib angle, jib extension length, jib load and bucket load. Visual and audible warnings at the upper controls indicate to the operator if the equipment approaches 90 percent of the maximum allowable capacity. By providing real-time feedback, including maximum allowable and actual capacities of bucket and jib, lineworkers can take corrective measures to prevent overload situations.
For companies that have implemented the Load Alert system, several unexpected outcomes have occurred. Initially there was pushback from operators who felt like Big Brother was watching them. But now that trucks with the system are in the field, lineworkers have been surprised to find they were unintentionally overloading the basket or jib and could take immediate corrective action. The system also aids during training, and operators can be more accurate in setup, estimated weights, angles and other factors.
In addition, users have the option to collect data through telematics to be used for operator training and notifications. Utilities can track historical occurrences of overload situations and use the information to perform required inspection and maintenance as necessary. It also can guide training needs and aid in determining what is needed for future equipment purchases. When an overload occurs, an alert can be sent to a designated person via text or email, capturing the exact aerial configuration at the time of the overload. This information can be used in overload event investigations to recreate the work scenario and determine a training exercise that is anything but hypothetical.
System information also aids utility fleets in making more effective purchases by providing fleet managers data about, for example, how often a jib is used or the average weights of loads lifted or how much basket capacity typically is used. This can result in savings by reducing equipment purchase costs, or it might support a fleet manager’s proposal to buy an aerial device with higher capacities for applications that warrant it.
Ultimately, it’s all about the numbers. Operators are responsible for calculating loads in the bucket and on the jib and verifying them against available capacity. New technologies can aid in those processes, increasing accuracy, but they cannot replace the operator’s knowledge – and following – of safe work practices.
About the Author: Dan Brenden is director of engineering at Terex Utilities (www.terex.com/utilities). He has more than 18 years of experience as a product manager for Terex.
Here are seven best practices to help operators prevent aerial device overloads in the field.