Glossary of Terms for Overhead Cranes

Abnormal Operating Conditions:
Environmental conditions that are unfavourable or harmful for the operation of a hoist, such as excessively high (over 40 C.) or low (below -10 C.) ambient temperatures, corrosive fumes, dust laden or moisture laden atmospheres, and hazardous locations.

Adjustable or Variable Voltage:
A method of control by which the motor supply voltage can be altered.

Anchor Bolt Load:

The total amount of force that is applied to each supporting anchor bolt; usually measured in kips.

Automatic Crane:
A crane that operates through a preset cycle of actions.

Auxiliary Hoist:
A supplemental hoisting unit, usually designed to handle lighter loads at a higher speed, to the main hoist.

Axial Load:
The total vertical force applied to the supporting structure. Formula: Axial load = (overall weight of the crane) + (design factor x weight of load).

Bearing Life Expectancy:
The L-10 life of an anti-friction bearing is the minimum expected life, hours, of 90 percent of a group of bearings, which are operating at a given speed and loading. The average expected life of the bearings is approximately five times the L-10 life.

The horizontal beam (track) upon which the hoist trolley travels. The “jib” of the jib crane.

Box Section:
The rectangular cross section of girders, trucks or other members enclosed on four sides.

A device, other than a motor, used for slowing or stopping motion by friction or power means in the overhead crane.

Bracket Center:
The distance, center line to center line, between two supporting brackets of a wall mounted jib crane (i.e. the distance between the two wall mounting points).

Branch Circuit:
The circuit conductors between the final overcurrent device protecting the circuit and the outlet(s).

That part of an overhead crane consisting of girders, trucks, end ties, and drive mechanism which carries the trolley and travels in a direction parallel to the runway.

Bridge Conductors:
The electrical conductors located along the bridge structure of a crane to provide power to the trolley.

Bridge Length:
The total, overall, length of a bridge. Note: the working length or hook coverage of the bridge is less than the overall bridge length.

Bridge Rail:
The rail supported by the bridge girders on which the trolley travels.

An energy absorbing device for reducing impact when a moving crane or trolley reaches the end of its permitted travel, or when two moving cranes or trolleys come into contact.

Buffer Assembly:
A floating spacer that rides in the runway between two bridges (or hoist trolleys) to prevent a concentrated overload between hanger points. It physically separates the bridge or trolleys a minimum distance apart.

The slight upward vertical curve given to girders to compensate for deflection.

The maximum live weight that the crane is designed to support. For jib cranes, the design load is based on the capacity, plus a hoist & trolley allowance (15% of capacity) and an impact allowance (25% of capacity). The allowable deflection of the crane is calculated using the design load plus the hoist allowance. Load testing can be performed to 125% of rated load capacity. Standard capacities vary between manufacturers.

Minimum distance from the extremity of a crane to the nearest obstruction.

Contacting devices for collecting current from the runway or bridge conductors. The mainline collectors are mounted on the bridge to transmit current from the runway conductors, and the trolley collector are mounted on the trolley to transmit current from the bridge conductors.

Contactor, Magnetic:
An electro-magnetic device for opening and closing an electric power circuit.

A device for regulating in a predetermined way the power delivered to the motor or other equipment.

A method of control by which the motor is reversed to develop power to the opposite direction.

The column of a free standing bridge crane is one of the “legs” on which the crane stands, and is made of square tube.

Cross Shaft:
The shaft extending across the bridge, used to transmit torque from the motor to bridge drive wheels.

Cushioned Start:
An electrical or mechanical method for reducing the rate of acceleration of a travel motion.

Dead Loads:
The loads on a structure, which remain in a fixed position relative to the structure. On a crane bridge such loads include the girders, footwalk, cross shaft, drive units, panels, etc.

The difference in elevation at the tip of the boom between an unloaded crane and a fully loaded crane; usually measured in inches.

Design Factor:
A multiplier incorporated into a formula to allow for variations in the properties of materials, manufacturing, operations, conditions, and design assumptions. Design factors are based upon the capacity of the crane, plus 15% for the weight of the hoist, plus an additional 25% for impact. It is important to distinguish the design factor from the safety factor, which is a much larger number (typically 4 – 8 times greater than the design factor).

A plate or partition between the opposite parts of a member serving a definite purpose in the structural design of the member.

Drive Girder:
The girder on which the bridge drive machinery is mounted.

Dynamic Lowering:
A method of control by which the hoist motor is so connected in the lowering direction, that when it is overhauled by the load, it acts as generator and forces current either through the resistors or back into the line.

Eddy-Current Braking:
A method on control by which the motor drives through an electrical induction load brake.

Efficiency of Gearing and Sheaves:
The percentage of force transmitted through these components that is not lost to friction.

Electric Overhead Traveling Crane:
An electrically operated machine for lifting, lowering and transporting loads, consisting of a movable bridge carrying a fixed or movable hoisting mechanism and traveling on an overhead runway structure.

Electrical Braking System:
A method of controlling crane motor speed when in an overhauling condition, without the use of friction braking.

Enclosed conductor(s):
A conductor or group of conductors substantially enclosed to prevent accidental contact.

A housing to contain electrical components.

End approach:
The minimum horizontal distance, parallel to the runway, between the outermost extremities of the crane and the centerline of the hook.

End tie:
A structural member other than the end truck which connects the ends of the girders to maintain the squareness of the bridge.

End Truck:
The unit consisting of the truck frame, wheels, bearings, axles, etc., which supports the bridge girders.

A provision designed to automatically stop or safely control any motion in which a malfunction occurs.


Cabling systems used to manage cables and hoses which provide power, gas, or liquid to moveable machinery on the cranes.

Fixed axle:
An axle which is fixed in the truck and on which the wheel revolves.

Floor-Operated Crane:
A pendant controlled crane on the floor or an independent platform.

The walkway with handrail and toeboards, attached to the bridge or trolley for access purposes.

The decking or floor that the crane sits on that also supports the crane as it lifts. Many free standing jib cranes do not require a special foundation; they can be used with a standard 6-inch reinforced concrete floor. However, some jib cranes require a special foundation of concrete and steel, a few feet wide and deep.

Gantry Crane:
A crane similar to an overhead crane except that the bridge for carrying the trolley or trolleys is rigidly supported on two or more legs running on fixed rails or other runway.

The principal horizontal beams of the crane bridge which supports the trolley and is supported by the end trucks.

Ground Fault:
An accidental conducting connection between the electrical circuit and the earth (ground) or some conducting body that serves in place of the earth.

Hanger Assemblies:
The devices which connect a ceiling mounted bridge crane or monorail to the supporting structure.

The horizontal member of a free standing bridge crane’s support structure, made of two back-toback channels, from which the runways are hung.

Height Under Boom (HUB):
The distance from the floor to the underside of the crane’s boom. The minimum height under boom equals the height of the load, plus the maximum distance the load is to be lifted, plus the headroom required for the hoist, trolley, and attachments.

A machinery unit that is used for lifting and lowering a load.

Holding Brake:
A stopping mechanism that automatically prevents motion when power is off.

Hook Approach:
The minimum horizontal distance between the center of the runway rail and the hook.

Hydraulic Brake:
A brake that provides stopping motion by hydraulic means.

Impact Allowance:
Additional hook load assumed to result from the dynamic effect of the live load.

Insulation Class:
Motor winding insulation rating which indicates its ability to withstand heat and moisture.

Inverter (Variable Frequency Drive):
A method of control by which the fixed line voltage and frequency is changed to a three-phase system with infinitely variable voltage and frequency.

A unit of force, equivalent to 1000 force-pounds, of stress intensity commonly used in engineering to measure loads. Expressed as K.S.I.

Knee Brace:
The diagonal structural member joining the building column and roof truss.

Lateral Forces:
Horizontal forces perpendicular to the axis of the member being considered.

Maximum safe vertical distance through which the hook, magnet, or bucket can move.

Lift Cycle:
Single lifting and lowering motion (with or without load)

Lifting Devices:
Buckets, magnets, grabs and other supplemental devices, the weight of which is to be considered part of the rated load, used for ease in handling certain types of loads.

Limit Switch:
A device designed to cut off the power automatically at or near the limit of travel for the crane motion.

Line Contactor:
A contractor to disconnect power from the supply lines.

Live Load:
A load which moves relative to the structure under consideration.

Load Block:
The assembly of hook, swivel, bearing, sheaves, pins and frame suspended by the hoisting ropes.

Load Carrying Part:
Any part of the crane in which the induced stress is influenced by the load on the hook.

Load Cycle:
One lift cycle with load plus one lift cycle without load.

Longitudinal Stiffeners:
Horizontal members attached to the web of the bridge girder to prevent web buckling.

Magnetic Control:
A means of controlling direction and speed by using magnetic contactors and relays.

Main Line Contactor:
A magnetic contactor used in the incoming power circuit from the main line collectors.

Main Line Disconnect Switch:
A manual switch which breaks the power lines leading from the main line collectors.

Manual-Magnetic Disconnect Switch:
A power disconnecting means consisting of a magnetic contactor that can be operated by remote pushbutton and can be manually operated by a handle on the switch.

The vertical steel component of the jib crane which supports the crane.

Master Switch:
A manually operated device which serves to govern the operation of contactors and auxiliary devices of an electric control.

Match Marking:
Identification of non-interchangeable parts for re-assembly after shipment.

Mechanical Load Brake:
An automatic type of friction brake used for controlling loads in the lowering direction. This unidirectional device requires torque from the motor to lower a load but does not impose additional load on the motor when lifting a load.

Mean Effective Load:
A load used in durability calculations accounting for both maximum and minimum loads.

Mill Duty Crane:
Service classification covered by AISE Standard No. 6, Specification for Electric Overhead Traveling Cranes for Steel Mill Service.

Multiple Girder Crane:
A crane which has two or more girders for supporting the live load.

Non-coasting Mechanical Drive:
A drive with coasting characteristics such that it will stop the motion within a distance in feet equal to 10 percent of the rated speed in feet per minute when traveling at rated speed with rated load.

Overall Height:
The distance to the highest point on the jib crane (should include hardware). A minimal clearance (nominally 3 inches) is required from any obstructions above the boom or tie rod assembly throughout the entire rotation of the crane.

Any load greater than the rated load.

Overload Limit Device:
Refer to Section 4.3 for a complete definition.

Overload Protection (Overcurrent):
A device operative on excessive current to cause and maintain the interruption or reduction of current flow to the equipment governed.

Overall Height:
The distance to the highest point on the jib crane (should include hardware). A minimal clearance (nominally 3 inches) is required from any obstructions above the boom or tie rod assembly throughout the entire rotation of the crane.

Pendant Pushbutton Station:
Means suspended from the crane operating the controllers from the floor or other level beneath the crane.

Pitch Diameter (Rope):
Distance through the center of a drum or sheave from center to center of a rope passed about the periphery.

Plain Reversing Control:
a reversing control which has identical characteristics for both directions of motor rotation.

A control function which accomplishes braking by reversing the motor line voltage polarity or phase sequence.

Protective Panel:
An assembly containing overload and undervoltage protection for all crane motions..

Rated Load:
The maximum load which the crane is designed to handle safely as designated by the manufacturer.

Regenerative Braking:
A method of controlling speed in which electrical energy generated by the motor is fed back into the power system.

Regulated Speed:
A function which tends to maintain constant motor speed for any load for a given speed setting of the controller.

Remote Operated Crane:
A crane controlled by an operator not in a pulpit or in the cab attached to the crane, by any method other than pendant or rope control.

Resistor Rating:
Rating established by NEMA which classifies resistors according to percent of full load current on first point and duty cycle.

Rotating Axle:
An axle which rotates with the wheel.

Running Sheave:
A sheave which rotates as the hook is raised or lowered.

The rails, beams, brackets and framework on which the crane operates.

Runway Conductors:
The main conductors mounted on or parallel to the runway which supplies current to the crane.

Runway Rail:
The rail supported by the runway beams on which the bridge travels.

Skewing Forces:
Lateral forces on the bridge truck wheels caused by the bridge girders not running perpendicular to the runways. Some normal skewing occurs in all bridges.

For a jib crane, span is the distance from the center of the pivot point to the end of the boom. The distance between the center line of the runways. Note that span is greater than actual “working span” or “hook coverage” but is smaller than overall length of the bridge.

Splice Joint:
Used when joining runway track sections together. A track splice is used to splice the track sections together, and an additional truss splice plate is required if trussed runways need to be joined.

Static Control:
A method of switching electrical circuits without the use of contacts.

Stepless Control:
A type of control system with infinite speed control between minimum speed and full speed.

Stepped Control:
A type of control system with fixed speed points.

A device to limit travel of a trolley or crane bridge. This device normally is attached to a fixed structure and normally does not have energy absorbing ability.

Supporting Structure:
The foundation which the crane is bolted to or implanted in, typically at least six inches of concrete is sufficient for most installations. Acculift will measure and advise on the supporting structural requirements of your desired crane system.

Support Center:
The distance between the center line of the two support columns or hangers along a runway. Note that support centers determine what track style is required.

Maximum lateral deviation from straightness of a structural member, measured at right angles to the Y-Yaxis.

Supporting Structure:
For a free standing bridge crane, the supporting structure refers to the support assembly, also called the goal post or end frame, consisting of the columns and header. For a ceiling mounted system, the supporting structure is the ceiling, including trusses, stringers, columns, etc., from which the crane is hung.

Totally enclosed fan cooled.

Totally enclosed non-ventilated.

Thrust & Pull:
Forces exerted by a crane on its supporting structure. Thrust is the pushing (or compressive) force exerted on the structure, while Pull is the tensile force. Thrust and Pull are thus equal (but opposite in direction) to each other. The maximum thrust & pull occurs when the crane is loaded at full capacity.

Torque, Full Load (Motor):
The torque produced by a motor operating at its rated horsepower and speed.

Torsional Box Girder:
Girder in which the trolley rail is located over one web.

Torsional Forces:
Forces which can cause twisting of equipment or object due to applied torque.

The unit carrying the hoisting mechanism which travels on the bridge rails.

Trolley Frame:
The basic structure of the trolley on which are mounted the hoisting and traversing mechanisms.

Trolley Saddle Height (TS):
On a Free Standing Bridge Crane, this is the height from the top of the saddle of the hoist trolley (the clevis pin from which the hoist is actually hung) to the floor

True Vertical Lift (TVL):
Also known as plumb lift, TVL means that there is no sideways movement when the hook is lifted and lowered.

Undervoltage Protection:
A device operative on the reduction or failure of voltage to cause and maintain the interruption of power in the main circuit.

Variable Frequency:
A method of control by which the motor supply voltage and frequency can be adjusted.

Voltage Drop:
The loss of voltage in an electric conductor between supply tap and load tap.

Web Plate:
The vertical plate connecting the upper and lower flanges or cover plates of a girder.

Distance from center-to-center of outermost wheels.

Wheel Load:
The load without impact on any wheel with the trolley and lifted load (rated capacity) positioned on the bridge to drive maximum loading.

Working Span:
The working span (or hook coverage) is less than the span of the crane. It is a function of the maximum hook reach and the ability to get the trolley close to the mast.

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