NCCCO Digger Derrick key terms

The product of a load's weight and its horizontal distance from the tipping axis or boom pivot; used to judge whether a lift stays within the derrick's rated capacity.

The horizontal distance from the derrick's rotation center to the vertical centerline of the load, measured with the boom at the working angle and extension.

The maximum load a digger derrick may handle at a given radius, boom configuration, and outrigger setup, as published by the manufacturer in the capacity chart.

The manufacturer's table or graph showing allowable loads for combinations of boom length, boom angle, radius, and outrigger position; the controlling reference for every lift.

The capacity at which the machine would tip, based on weight and geometry; always lower than the structural limit and the governing limit for most derrick lifts.

The capacity at which a component such as the boom, winch, or rotation bearing would fail from stress; it controls only when it is lower than the stability limit.

The line about which the machine would overturn, normally through the outrigger pads or the track/tire contact points on the loaded side.

The ground-contact plate under an outrigger float that spreads the outrigger's downward force over a larger area to keep soil bearing pressure acceptable.

The cylindrical or rectangular foot attached to the outrigger cylinder that transfers force to the pad or cribbing and allows the leg to be set on uneven ground.

Wood, composite, or steel blocking placed under outrigger pads to spread load, level the machine, and bridge soft spots or voids in the ground.

The force per unit area that an outrigger pad or tire imposes on the soil; must stay below the soil's capacity to prevent settlement or punch-through.

An underground cavity such as a septic tank, culvert, basement, or utility trench that can collapse under outrigger loading even when the surface appears solid.

A designated person who watches the load, boom, and surroundings and relays hand signals or radio instructions to the operator when the view is obstructed.

The qualified individual who directs the operator's movements by voice, radio, or hand signals and who must be identifiable to the operator at all times.

Standardized arm and hand movements used to command boom, winch, rotation, and outrigger functions when radio communication is unavailable or fails.

A single emergency command, given by voice, radio, or hand, that requires the operator to halt all movement immediately; anyone on site may give it.

The closest distance any part of the machine, load, or personnel may come to an energized line, set by the utility's table for the line's voltage.

An overhead or underground conductor that is carrying voltage; it must be treated as live until the utility confirms de-energization and visible grounding.

A work area where all conductive objects and the worker are bonded together so they sit at the same potential, preventing current from flowing through the body.

Connecting equipment, conductors, or the machine frame to earth or to a common point so fault current has a low-resistance path away from workers.

The condition of a line or circuit that has been disconnected from all sources and verified by test; it must also be grounded before contact work begins.

The rotating helical flighting tool on the derrick's Kelly bar that bores holes in soil for poles, anchors, and foundations.

The telescoping or fixed square/hexagonal shaft that transmits rotation from the derrick's digger motor to the auger while allowing it to travel up and down.

Sudden reverse rotation of the auger or handle when flighting binds in rock, roots, or clay, capable of throwing a worker or spinning the boom.

Contact between the load block or hook and the boom tip that can shock-load or damage the boom; prevented by an anti-two-block device and limit switches.

A sensing system that warns the operator and stops hoisting or boom lowering before the load block contacts the boom tip.

An instrument that measures boom angle, length, and pressure or force to display radius, capacity, and an alarm as the machine nears its rated limit.

The angle between the boom centerline and horizontal, measured by an indicator; it directly affects radius and therefore capacity for a given boom length.

The amount of telescoping boom section deployed; each extension changes the load chart and must match the configuration assumed in the capacity table.

The large geared bearing that carries the turntable and boom loads and allows the upper structure to swing relative to the chassis.

A device that holds or slows rotation of the upper structure so the boom and load do not drift when the operator releases the swing control.

The rotating platform that mounts the boom, winch, and operator station and pivots on the rotation bearing above the chassis.

Ballast mounted opposite the boom to offset load moment and improve stability; it must never be altered or removed without manufacturer approval.

A curved gripping attachment or sling that clamps a pole for lifting and setting, sized to the pole's diameter and weight.

A synthetic or wire rope choker or basket rigged around a pole to lift it; must be rated for the load and inspected for cuts and abrasion.

The operation of lifting a pole, guiding it into a prepared hole, plumbing it, and backfilling or tamping it to final alignment.

A rope attached to a load so a worker standing clear can control rotation and swing without touching the load or standing under it.

A sudden application or release of load, such as a jerking hoist or a slipping sling, that produces forces well above the static weight.

The documented walk-around and function check of fluids, tires, outriggers, wire rope, hooks, latches, alarms, and controls performed before each shift.

Examination of the load line for broken wires, corrosion, kinks, and core protrusion, with removal criteria set by the manufacturer and applicable standards.

Operating each control through its range without a load to confirm smooth response, correct direction, and proper function of limit switches and alarms.

The procedure of isolating energy sources, applying locks and tags, and verifying zero energy before maintenance or repair on the machine.

A material property describing resistance to conducting electricity; fiberglass booms and insulating links are rated for specific voltages and must be kept clean and dry.