Electric Overhead cranes

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Electric Overhead Crane

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Cranes are industrial machines that are mainly used for materials
movements in construction sites, production halls, assembly
lines, storage areas, power stations and similar places.
Their design features vary widely according to their major
operational specifications such as:
 type of motion of the crane structure
 weight and type of the load
 location of the crane
 geometric features
 operating regimes
 environmental conditions.
ELECTRIC CRANES

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Electrically operated crane can be divided into
different sections as follows:
 Bridge girders
 End carriages
 Hoisting trolley also known as crab
 Long travel machinery
 Driver’s cabin/Floor operation

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A crane with a single or multiple girder
(bridge girder) bridge carrying a
movable or fixed hoisting mechanism
and traveling on an overhead fixed
runway structure with all or most
movements powered by electric motors
Electric Overhead Crane

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Single Girder Overhead Crane

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Fixed and Wire Rope Hoist

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When selecting an electric overhead traveling crane, there
are a number of requirements to be taken into account
 What specifications, codes or local regulations
are applicable?
 What crane capacity is required?
 What is the required span?
 What is the lift required by the hoist
Requirements in EOT Crane selection

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 What will be the duty cycle (usage) of the
crane?
 What is the hoist weight? Do you need the use
of a second hoist on the bridge crane?
 What length of runway system is desired?
 What will the operating environment be (dust,
paint fumes, outdoor, etc)?
 What are the necessary crane and trolley
speeds?

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 What is the supply voltage/phases/amperage?
 What control system is desired?
 What safety considerations are to be
followed?
 Consider maintenance aspects of the crane.
 Consider other accessories such as lights,
warning horns, weigh scales, limit switches,
etc.

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There are various types of overhead cranes with
many being highly specialized, but the great
majority of installations fall into the following:
 Single girder cranes - The crane consists of a
single bridge girder supported on two end
trucks. It has a trolley hoist mechanism that runs
on the bottom flange of the bridge girder.
TYPES OF ELECTRIC OVERHEAD CRANES

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Single Girder Crane

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The crane consists of two bridge girders supported
on two end trucks. The trolley runs on rails on the
top of the bridge girders.
Double Girder Crane

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These cranes are essentially the same as the
regular overhead cranes 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.
These “legs” eliminate the supporting runway and
column system and connect to end trucks which
run on a rail either embedded in, or laid on top of,
the floor.
Gantry Cranes

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For some applications such as production assembly line
or service line, only a trolley hoist is required.
The hoisting mechanism is similar to a single girder
crane with a difference that the crane does not have a
movable bridge and the hoisting trolley runs on a fixed
girder.
Monorail beams are usually I-beams (tapered beam
flanges).
Monorail Cranes

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A common misconception is that double girder cranes are more
durable, per the industry standards (CMMA/DIN/FEM), both
single and double girder cranes are equally rigid, strong and
durable.
This is because single girder cranes use much stronger girders
than double girder cranes. The difference between single and
double girder cranes is the effective lifting height.
However, not every crane can be a single girder crane.
Generally, if the crane is more than 15 ton or the span is more
than 30m, a double girder crane is a better solution.
Single Girder or Double Girder

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Single Girder Cranes
 Single girder bridge cranes generally have a maximum span
between 20 and 50 feet with a maximum lift of 15-50 feet.
 They can handle 1-15 tonnes with bridge speeds approaching
a maximum of 200 feet per minute(fpm), trolley speeds of
approximately 100 fpm, and hoist speeds ranging from 10-60
fpm.
 Single girder cranes reduce the total crane cost on crane
components, runway structure and building
The advantages and limitations of Single /
Double Girder Cranes

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 They are faster, with maximum bridge speeds, trolley speeds and
hoist speeds approaching 350 fpm, 150 fpm, and 60 fpm,
respectively.
 They are useful cranes for a variety of usage levels ranging from
infrequent, intermittent use to continuous severe service. They can
lift up to 100 tons.
 These can be utilized at any capacity where extremely high hook lift
is required because the hook can be pulled up between the girders.
 They are also highly suitable where the crane needs to be fitted
with walkways, crane lights, cabs, or other special equipment.
Double Girder Cranes

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Under running cranes
Under Running or under slung cranes are distinguished
by the fact that they are supported from the roof
structure and run on the bottom flange of runway
girders.
They are typically available in standard capacities up to
10 tons (special configurations up to 25 tons and over
90 ft spans).
ELECTRIC OVERHEAD TRAVELLING (EOT) CRANE
CONFIGURATION

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• Very small trolley approach dimensions meaning maximum
utilization of the building's width and height.
• The possibility of using the existing ceiling girder for securing the
crane track.
Advantages of Under Running Crane

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Top Running Cranes
The crane bridge travels on top of rails mounted on a runway
beam supported by either the building columns or columns
specifically engineered for the crane.
Top Running Cranes are the most common form of crane
design where the crane loads are transmitted to the building
columns or free standing structure.
These cranes have an advantage of minimum headroom /
maximum height of lift.
ELECTRIC OVERHEAD TRAVELLING (EOT) CRANE
CONFIGURATION

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Double Girder Top Running Overhead Bridge Crane

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Bridge - The main traveling structure of the crane which spans the
width of the bay and travels in a direction parallel to the runway.
The bridge consists of two end trucks and one or two bridge girders
depending on the equipment type. The bridge also supports the
trolley and hoisting mechanism for up and down lifting of load.
End trucks - Located on either side of the bridge, the end trucks
house the wheels on which the entire crane travels. It is an
assembly consisting of structural members, wheels, bearings, axles,
etc., which supports the bridge girder(s) or the trolley cross
member(s).
Bridge Girder(s) - The principal horizontal beam of the crane bridge
which supports the trolley and is supported by the end trucks.

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Runway - The rails, beams, brackets and framework on which the crane operates.
Runway Rail - The rail supported by the runway beams on which the crane travels.
Hoist - The hoist mechanism is a unit consisting of a motor drive, coupling, brakes,
gearing, drum, ropes, and load block designed to raise, hold and lower the maximum rated
load. Hoist mechanism is mounted to the trolley.
Trolley - The unit carrying the hoisting mechanism which travels on the bridge rails in a
direction at right angles to the crane runway. Trolley frame is the basic structure of the
trolley on which are mounted the hoisting and traversing mechanisms
Bumper (Buffer) - 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. This device may be attached to the bridge; trolley or runway stop.

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Crane Capacity – The rated load, the crane will be
required to lift. Rated load shall mean the maximum load
for which a crane or individual hoist is designed and built
by the manufacturer and shown on the equipment
identification plate.
Dual operating speeds, normally a fast and slow speed
with a ratio of 4:1 are commonly used but for optimum
control a variable speed control system is strongly
recommended. Specifying
Essential parameters for specifying EOT cranes

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Electrical Requirements - (OSHA 1910.179 Overhead &
Gantry Cranes Regulations) specify the circuit voltage shall not
exceed 600 volts for AC or DC current. The runway power is
usually by conductor bar and hoisting trolley by festoon cable.
Control Requirements - The control circuit voltage at
pendant pushbuttons shall not exceed 150 volts for AC and
300 volts for DC.
Other control options including radio control, free-floating
pendant (festooned) or hoist-mounted pendant requirements
must be stated.

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CLASSIFICATION OF CRANES

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Two cranes with the same rated capacity and span may differ in their
average load intensity and/or expected loading cycles. There are
different standards which classifies cranes based on the service class.
The Crane Manufacturer Association of America (CMAA) classifies
bridge cranes according to average load intensities and number of
cycles.
On the other hand, the classification all hoists by the International
Organization for standardization (ISO), European Federation Standard
(FEM) and Hoist Manufacturer Institute (HMI) is according to more
rigorous requirements, which include number of starts and maximum
running time per hour.
CLASSIFICATION OF CRANES

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Class A (Standby or Infrequent service)
This crane is the lightest crane as far as duty cycle is
concerned. Example of the use of Class A cranes are
transformer station, power houses, turbine halls, motor
rooms and public utilities etc.
Class B (Light service)
This service class covers cranes where service
requirements are light and speed is slow. Examples of
class B cranes include service buildings, light assembly
operations, repair and maintenance shops and light ware
housing etc.

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Class C (Moderate service)
Cranes whose service requirements are deemed
moderate. Examples of class C cranes are the cranes
usually used in paper mill machine rooms and machine
shops etc.
Class D (Heavy service)
In class D crane service, loads approaching 50% of the
rated capacity is handled constantly during the work
period. Typical examples of cranes with heavy service are
steel warehouses, foundries, fabricating shops, heavy
machine shops container yards and lumber mills etc.

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Class E (Severe service)
Cranes with class E service are capable of handling
loads approaching the rated capacity throughout its
life with 20 or more lifts per hour at or near the rated
capacity.
Application of canes with class E include magnet,
bucket, magnet/bucket combination cranes or
fertilizer plants, cement plants, scrap yards, lumber
mills and container handling etc.

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Class F (Continuous Severe Service)
Cranes with class F service are to be capable of handling
loads approaching rated capacity continuously under
severe service conditions throughout its life.
Typical examples of such cranes include custom designed
specialty cranes essential for performing the critical work
tasks affecting the total production facilities.
This type of crane must provide the highest reliability with
special attention to ease of maintenance features.

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A device used for lifting or lowering a load by means of a drum or
lift-wheel around which rope or chain wraps.
Cranes and Hoists are somewhat interchangeable terminology since
the actual lifting mechanism of a crane is commonly referred to as a
hoist. Hoists may be integral to a crane or mounted in affixed
position, permanently or temporarily.
When a hoist is mounted to a trolley on a fixed monorail, two
directions of load motion are available: forward or reverse, up or
down.
When the hoist is mounted on a crane, three directions of load
motions are available: right or left, forward or reverse, up or down.
HOISTS

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Three methods of applying power for overhead hoists
• Manual – By hand Chain
• Electric - The most common power source
application
• Pneumatic - Often required in applications of high
speed, higher duty cycle involving rapid, repetitive
tasks or hazardous areas where electric power is
inadvisable.
Overhead Hoist Power Application

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There are various types of hoists that perform a wide
range of basic lifting functions. These can be categorized
as packaged hoists or specially engineered hoists.
The packaged hoists include hand chain, ratchet lever;
electric chain and electric wire rope hoists.
Choosing the right hoist type and model generally,
depends on the number of lifts per day and the average
weight.
HOIST TYPES

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Ratchet Lever - Small, hand powered hoist capable of lifts
between 3/4 ton to 6 tons with standard lifts between 5 feet and
15 feet.
Capable of lifting, pulling and stretching loads vertically and
horizontally; light, portable - often carried site-to-site
Hand Chain - Hand powered chain hoist capable of lifts
between 1/2 ton and 25 tons with standard lifts between 8 feet
and 20 feet.
Normally hook mounted to a fixed point or trolley; provides true
vertical lift; lifts are slow and require high work effort; precise
load spotting.

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Electric Chain- Capable of lifts between 1/2 ton and 3 tons
with standard lifts between 10 feet and 20 feet (1/2 and one
ton) and 10 and 15 feet (one to 3 tons).
Extended lifts are possible after factory modifications.
Operated by pushbutton control; powered by electric motor;
controlled by an electric motor brake; equipped with upper
and lower travel limit stop.
Electric Wire Rope - Capable of lifts between 1/8 ton and 5
tons with standard lifts between 15 feet and 30 feet. Operated
by pushbutton control; designed for heavy-duty and high-
performance lifting.

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CRANE ELECTRIFICATION
&
POWER SUPPLY

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There are two circuits in most hoist electrification systems, power and
control.
 Power Circuit
The power circuit provides the energy to lift loads, and run other
motors that perform work. Since bridges, trolleys, and hoists move
during operation there must be powered by appropriate means.
 Control Circuit
Another secondary low voltage electrical circuit supply power to the
control functions. The crane or hoist is normally operated by some type
of pushbutton arrangement held in an operator’s hand. The benefit of
reducing shock hazard by reducing the voltage and current are obvious.
CRANE ELECTRIFICATION & POWER SUPPLY

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Cable Reel – Round cable stored in a spring
winder. The advantage of these systems is that it
takes up less space and advantageous in curves.
Not recommended for manual trolleys.
Coiled Cable – Round cable coiled in a spiral (like
telephone cord). It is inexpensive compared to
other types but becomes tangled after a time.
Methods of Crane Electrification

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Electric Gantry Crane Power Cable Reel

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Insulated power bars
This method uses insulated bars with sliding shoe collector
system, which removed the most of the exposed conductor
safety hazard and provides an option of very high amperage
compared to other power systems.
Although this is an improvement over other methods, the shoes
wore out quickly.
Festoon
Flat cable on a trolley traveling on a C rail provides direct
contact, which is extremely wear resistant. This system
provides advantage of superior reliability. However, this method
is not recommended for curves

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Copper Insulated Shrouded Conductor Bus bar for Crane
Mobile Power Supply

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Note:
At the present time insulated power bar is the preferred
choice for crane runway electrification while festooning is
the choice for bridge cross conductors and floating
pushbuttons.
Routing festoon systems becomes somewhat of a problem
when more than one separately moving system must
operate on the same runway or bridge.
When you consider that two or more bridges often operate
on one runway system, use of the insulated bar for runways
makes sense.

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MOTORS AND CONTROLS

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Depending on the application, the EOT cranes
require motors at three areas:
Bridge and end truck motors
Trolley motors
Hoist motors
MOTORS AND CONTROLS

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1. Motors shall be fixed, dual or variable speed drive and
shall be suitable for quick reversing crane duty.
The motors shall be high-starting-torque, high-slip, squirrel-
cage AC motor or alternatively where specified shall be a
variable-speed, low-slip, wound-rotor AC motor.
2. Drives shall be rated to carry the full load current of the
hoist motors continuously for 10 minutes.
Drives shall be rated to carry the full load current of the long
and cross travel motors continuously for 5 minutes
Motor Specifications

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3. If using variable speed drives, the adjustable drive shall be
vector control and closed loop encoders for control of hoist
motors or open loop vector for control of the bridge long
travel and cross travel trolley motors.
4. Motors shall be totally enclosed, non-ventilated type,
certified for 30-minute time-rated operation at full
identification plate power output in an ambient temperature
of 104ºF (40ºC), maximum temperature rise 167ºF (75ºC),
insulation not less than Class B system.
Motors for hazardous environment, where indicated, shall
be explosion proof.

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5. Motors shall not be built integral with the crane framework and
output shafts shall be tapered. The design shall include for
automatic application of motor brakes in the event of a failure of
the electronic circuitry or of the power supply.
6. Each motor shall be provided with a full magnetic, electrically
operated, reversing-type controller with thermal-overload
protection, fused disconnects switch, and control-circuit
transformer.
7. Enclosure shall be fitted with a UL-approved drain and breather
and shall be certified and labeled in accordance with UL 674, Class
1, Groups C and D.

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The enclosures house all of the electrical components
on the crane and are rated by the National Electrical
Manufacturers Association (NEMA) as to the level of
protection they provide from the conditions in the
surrounding environment.
Typically, the most common practice is to specify
NEMA 1 level of protection for all electrical equipment
and NEMA 12 for all controls panels.
ENCLOSURES

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Controls deserve special consideration, especially in high duty
classifications where response is crucial.
Unless otherwise specified, all crane functions shall be
controllable from the floor with radio remote control and from
the crane operator’s cab (if provided).
A pendent control station shall also be suspended from the
crane on an independent track, running approximately the full
span of the crane.
Cranes shall be able to be switched between remote and
pendent control.
CRANE CONTROLS

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1. Single- and two-speed controls have traditionally
been the controls of choice for light to moderate duty
crane applications (class B), since precise load
positioning is not as critical factor in most class B
applications.
2. Multi-speed control relies on three to five specific
speed points, which are produced by changing the
resistance of a wound rotor induction motor through
the use of magnetic contactors and resistor banks.

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3. AC static step-less control is suited for higher duty
applications (D-F), where high temperatures, or high dust or
corrosive gas conditions exist.
It is called “step-less” because it changes the inductance of a
wound rotor without the use of speed step magnetic
contactors to achieve infinitely variable speeds.
This control also uses an eddy current load brake on hoists,
and reduces maintenance by replacing contactors and relays
with potted, non-wearing solid state devices.

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4. Adjustable frequency is the state-of-the-art control
system in solid-state technology and now the
mainstay of Class D, E, and F cranes.
A micro-computer allows acceleration and deceleration
rates to be adjusted digitally and independently for smooth
stops and starts and unequalled inching capability.
And because of its solid-state construction, is has no
moving parts. It uses reliable, low-maintenance squirrel
cage motors and does not require eddy current load brakes
on hoists.

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Limit switch shall be provided to prevent power
being applied to the crane travel motor when the
crane track beam is interlocked to a fixed track
beam.
Operation of the interlock shall be controlled by
means of nylon ropes or chains with suspended,
unbreakable, insulated handles having appropriate
reach and location.
Handles shall be approximately 54 inches (1370
millimeter) above the operating floor level.

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Variable Frequency Drive (VFD) - A pendant can also be used
in conjunction with a Variable Frequency Drive.
A VFD is used to vary the frequency of the motors controlling
the motions allowing for smooth acceleration and
deceleration.
The buttons on the pendant operate a VFD unit operated in
much the same way as ‘Two Speed control’.
The first step is held to maintain the current speed while the
second step is used for acceleration.

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Deceleration shall be achieved by releasing the
button entirely. Pressing the button back to the
first step will maintain the new slower speed.
It should be noted that the deceleration shall not
be achieved through uncontrolled coasting but
through a programmable dynamic braking system.
The control provided by a VFD allows for a high
level of customization.

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Radio Control
The radio control performs exactly like the pendant
but operates using a radio frequency. The radio
control incorporates numerous safety features and
allows the operator a greater range of operator
motion than a pendant.
Radio control shall be from a portable console and
shall preferably utilize ‘Ethernet’ communications for
the link. As a backup to radio control all crane
functions shall also be controllable from the
pushbutton station.

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Shall be provided to prevent over travel of the hook or load block
in the hoisting direction.
Limit switches shall be arranged to stop the hoist motor and
apply the motor brake before reaching the uppermost safe limit
of travel.
In case of hook over travel, the motor shall be automatically and
momentarily reversed. Adjustable lower limit switch to stop the
hoist motor shall be provided.
Motor brake shall be applied when the load hook reaches a
predetermined lower limit.
Limit Switches

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According to OSHA, the hoist limit switch must be
operationally checked under no load at the
beginning of each shift.
The purpose of this check is two-fold. It not only
verifies the operation of the switch, it also
"exercises" the make/break mechanism, thus
reducing the chances of it "freezing up".
Limit Switches

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Upper and Lower Travel Safety Limit Switch
The Upper and Lower Travel Limit Switch is an automatic reset
type switch and connected to the control circuit. The switch
housing is recessed into the underside of hoist body.
The upper and lower limit switches are emergency protection
devices and are not to be used as a continuous stop. The hook
block activates the upper limit switch as it contacts the limit
switch that is located on bottom side of hoist body.
Once the switch is activated, the “UP” circuit is opened. The fall
stop activates the lower limit switch when hook block is lowered
to its lowest travel position. The limit switch is activated and
opens the “down” circuit.

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Upper and Lower Rotary Travel Limit Switch
(Optional Only on 3-Phase units)
The rotary limit switch is adjustable and provides
over-travel protection for the upper and lower
limits of hoist travel.
The limit switch is connected to the control circuit.
The length of air gap determines length of reset
play in opposite direction.

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Air Gap Adjustment
To reset the rotary limit once it has tripped, the load block assembly
must travel approximately 11” [27cm] in opposite direction

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Pendent Pushbutton Control Stations
Pushbuttons stations for crane control shall be heavy-
duty; oil tight, momentary contact devices with the
number of buttons and the marking of identification
plates in accordance with NEMA ICS 1.
Unit shall have a pendant-mounted conductor cable
with a permanently attached strain-reliever chain or
cable integral with the pendant conductor cable.
Control Equipment

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Pushbutton station shall be grounded to the hoist and
crane bridge. Strain-reliever chain or cable shall not be
used as a grounding circuit. Pushbuttons shall be
designed to transmit a distinct notch or step feeling to
the operator for each pressure or release action on
hand-controlled speed points
Pendant pushbuttons shall be legibly and permanently
marked and shall be vertically arranged in the
following top to bottom grouped order:

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TROLLEY FORWARD
TROLLEY REVERSE
BRIDGE FORWARD
BRIDGE REVERSE
UP, DOWN
RESET, STOP

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Stop control shall be red, plastic-covered,
mushroom-head button. A pilot light to indicate
that power is available shall be furnished integral
with the pushbutton cases.
An emergency stop pushbutton and a reset button
shall be provided to operate the main line
contactor.

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Radio Remote Control System
The main features of radio control system consist
of
• A portable transmitter
• An antenna and receiver on the bridge
• An intermediate relay panel on the bridge to
amplify the signals for the crane contactors

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Radio controls should be designed so that if the
control signal for any crane motion becomes
ineffective, that crane motion will stop, and
conversely signals received from any source other
than the transmitter will not result in operation of
any motion of the crane.
The crane must not take off on its own or respond
to or generate false commands. In case electricity
failure occurs" the crane must stop.

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A secure signal includes at least three
characteristics separately recognizable by the
receiver. An emergency stop device shall be used
for emergency stop.
Typical frequencies used for radio controls are in
between 450 - 470MH for which license is
required, and the recommended crane controls for
operating are of maximum 250 metre range.

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Remote controller labeled with the compass
points

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BRAKING
 The parts used for braking shall be made from hard
wearing material with adequate thermal capacity for the
duty required. Due allowance shall be kept for the brake
drum capacity to dissipate heat generated due to frequent
braking.
 The rubbing surface shall be smooth and free from
defects. The brake lining shall be protected, from water,
grease, oil or other adverse effects.
 The bearing pressure on the linings shall be conducive to
uniform braking and long life. Brakes shall be provided
with means of adjustment to compensate for wear.

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All electro-mechanical or electro-hydraulic brakes shall be
applied automatically by springs or weights when the power
supply to the brake is interrupted or when the circuit breaker is
opened or when the controller is brought to off position.
Power applied brakes shall not be fitted without a backup
system of power released type and without prior approval of the
purchaser.
Springs of electro-mechanical brakes shall be of the compression
type and shall not be stressed in excess of 80 percent of the
elastic limit of the material.

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Brakes
• Automatic brakes shall be provided for all
motions. Drum brakes are preferred on hoists
and should have taper bores to mate to the
gearbox/motor shafts.
• These shall be applied immediately the current
is switched off or fails from any cause. Brakes
may be applied by mechanical, electrical,
pneumatic, hydraulic, or gravity means.

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How is trolley and bridge braking accomplished

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There are 4 bridge brakes, one on each drive wheel

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There are 4 trolley brakes, one at each drive wheel

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Motor Brakes
Motor brakes shall be provided on electric-motor-
operated hoists, trolleys, and bridges.
Motor brake shall be an externally adjustable,
multiple friction electromagnetic disk brake which
shall apply automatically when the power is
interrupted.
Torque rating of the bridge and trolley brakes shall be
not more than 50 percent of the full-load torque of
the bridge and trolley motors and shall be adjustable
to 25 percent for all duty classes.

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Hoist Load Brake
Each hoisting unit shall be provided with two means of braking.
One brake shall be an electric motor brake as specified. The
other brake shall be a mechanical load brake, directly applied to
the hoist motor shaft or other shaft in the hoist gear reduction.
Hoist motor brake shall be capable of holding the capacity load
of the hoist at any point independent of the load brake and in
addition to stopping and safely holding 125 percent of the rated
load from any operating speed, shall hold a static load equal to
150 percent of the rated capacity.

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Eddy-Current Load Brake
Eddy-current-type brake shall be provided for hoist control
of wound-rotor motors. Eddy-current brakes shall provide
an adjustable varying artificial load on four lowering speed
points and on not less than two hoisting speed points.
When eddy current brakes and motors are not determined
from root-mean-square computations, the crane torque
rating of the eddy-current brakes shall be not less than 1.2
times the torque rating of the motor.

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Hoist Motion Brake
All electrically operated hoisting motion shall be fitted with
an electro-hydraulic/electro-magnetic fail safe brake.
The brake will arrest the motion and hold at rest any load
up to and including overload test load at any position of the
lift.
The provision shall be made to enable any load capable of
overcoming the friction in the system up to and including
the test load to be lowered safely in a controlled manner in
the event of power failure.

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Travelling Motion
Every electrically operated travelling motion shall be fitted with a
mechanical or hydraulic brake or an automatic electro-magnetic I
electro-hydraulic brake or a combination of the two, if required.
The brake shall be capable of bringing a fully loaded crane to rest
with least possible shock from the highest speed it can attain with
electro-magnetic/electro-hydraulic brakes, limit switches shall be
provided in this motion.
The travelling motion of every electric outdoor crane shall be
provided with the automatic electromagnetic -hydraulic parking
brakes if the service brake is not of eletro-mechanical type.

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Traversing Motion
The cross traverse motion should also necessarily be
provided with brake/brakes as specified for long travel
motion. When electro-mechanical brakes are provided, end
limit switches shall be provided in this motion.
The cross traverse motion brakes shall be capable of
bringing the fully loaded crab to rest with least possible
shock from highest speed it can attain. The braking torque
shall not be less than the full load torque transmitted to the
brake and shall not be more than the pullout torque of the
motor.

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Speed control systems are ideal for applications that
require the precise control of speed. Speed control
systems allow you to easily set and adjust the speed of
a motor.
The control system consists of a speed feedback
system, a motor, a driver (or speed control pack) and a
speed setting device. The motor for the speed control
system can be either a highly efficient brushless motor
or an AC motor.
DRIVES

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VARIABLE SPEED CONTROLS
Dynamic braking, controlled acceleration and deceleration,
and motor over-current and over- temperature protection
are some of the VFD features that provide better
performance and prolong the equipment life.
Dynamic braking is a technique of electric braking in which
the retarding force is supplied by the inverter. As the
operator releases the control device (pushbutton), the
output frequency of the inverter decreases to nearly zero
which brings the motor to almost a complete stop before
the brake is engaged

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Infinitely variable speed control gives the operator
the ability to smoothly accelerate, decelerated and
hold any speed between the defined minimum and
maximum speed.
Two-speed contactor control does not offer the
operator the ability to smoothly accelerate or
decelerate between the defined speeds
Variable Frequency Control Versus Two-speed
Contactor Control

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Standard squirrel-cage induction motors are usually
considered to be constant speed motors. These
systems require some means of throttling (via valves,
dampers, etc.) to meet process changes•
If a reduction in demand occurs, excess energy is
wasted in the control device (dampers, throttling
valves, recirculation loops) since the power delivered
does not decrease in proportion to the reduction in
demand.
CONVENTIONAL FIXED-SPEED AC SYSTEMS (AC MOTOR WITHOUT DRIVE)

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DC DRIVES
The DC motor is the simplest to which electronic
speed control can be applied because its speed is
proportional to the armature voltage. The DC voltage
can be controlled through a phase-controlled rectifier
or by a DC-DC converter if the input power is DC.
This is usually accomplished by a separate motor-
generator set producing a DC output. The speed of a
DC motor can be adjusted over a very wide range by
control of the armature current and/or field currents
(brushless DC drives, vector controlled DC drives).

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EDDY CURRENT CLUTCHES
Eddy current clutches can be used to control standard AC squirrel-
cage induction motors. However, they are low efficiency compared
to ASDs and have limited applications.
An eddy current clutch has essentially three major components: Ma
steel drum directly driven by an AC motor, a rotor with poles
and a wound coil that provides the variable flux required for speed
control.
A voltage is applied to the coil of wire, which is normally mounted
on the rotor of the clutch to establish a flux, and thus relative
motion occurs between the drum and its output rotor. By varying
the applied voltage, the amount of torque transmitted, and
therefore the speed, can be varied.

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VARIABLE VOLTAGE CONTROLLERS
Variable voltage controllers can be used with
induction motors. Motor speed is controlled
directly by varying the voltage. These controllers
require high slip motors and so are inefficient at
high speed. Only applications with narrow speed
ranges are suitable

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VARIABLE FREQUENCY DRIVES
A variable frequency drive controls the speed of an AC motor
by varying the frequency supplied to the motor.
The drive also regulates the output voltage in proportion to
the output frequency to provide a relatively constant ratio
(V/Hz) of voltage to frequency, as required by the
characteristics of the AC motor to produce adequate torque.
In closed-loop control, a change in demand is compensated by
a change in the power and frequency supplied to the motor,
and thus a change in motor speed (within regulation
capability).

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Speed control systems offer greater operating
precision and flexibility for your lifting equipment.
Travel and lift speed control system for
hoists and travelling cranes

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ADVANTAGES
• Reduces the pendulum effect and can even cancel it
• Increases the mechanical life span of suspended
cranes and the electrical life span of lift and trolley
motors.
• Increases productivity of your hoist station.
• Reduces energy consumption and the size of supply
lines.
• Reduces maintenance costs.
• Optimal utilization of work space
• Smaller investments and faster return on
investment.

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ADJUSTABLE SPEED DRIVE
An adjustable speed drive (ASD) is a device used to provide continuous
range process speed control (as compared to discrete speed control as
in gearboxes or multi-speed motors). An ASD is capable of adjusting
both speed and torque from an induction or synchronous motor.
An electric ASD is an electrical system used to control motor speed.
ASDs may be referred to by a variety of names, such as variable speed
drives, adjustable frequency drives or variable frequency inverters.
The latter two terms will only be used to refer to certain AC systems,
as is often the practice, although some DC drives are also based on the
principle of adjustable frequency.

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Designated person who is trained and experience in hand signals and is
understood by crane operators. One designated signalman will be
responsible for the control and coordination of any particular lift or Heavy
Rigging Activity.
Under certain conditions, such as multiple crane lifts, or lifting "in the
blind", it may be deemed necessary for additional signalmen to participate
in a lift or Heavy Rigging Activity.
One signalman will be designated as the “Lead Signalman”.
Signal Man

Standard Hand Signals For Controlling Overhead
And Gantry Cranes
HOIST. With forearm vertical, forefinger
pointing up, move hand in small horizontal
circle
LOWER. With arm extended
downward, forefinger pointing
down, move hand in small horizontal
circle.

And Gantry Cranes
BRIDGE TRAVEL. Arm extended
forward, hand open and slightly raised,
make pushing motion in direction of
travel.
TROLLEY TRAVEL. Palm up, fingers
closed, thumb pointing in
direction of motion, jerk hand
horizontally.

And Gantry Cranes
STOP. Arm extended, palm
down, hold position rigidly.
EMERGENCY STOP. Arm
extended, palm down, move
hand rapidly right and left.

And Gantry Cranes
MULTIPLE TROLLEYS. Hold up one
finger for block marked “1” and two
fingers for block marked “2”.
Regular signals follow.
MOVE SLOWLY. Use one hand to give any
motion signal and place other hand
motionless in front of hand giving the
motion signal. (Hoist Slowly shown as an
example.)

And Gantry Cranes
MAGNET IS
DISCONNECTED. Crane
operator spreads both
hands apart – palms up.

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SOME WIRING DIAGRAMS FOR CRANE
HOIST
&
THEIR SPEED

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WIRING DIAGRAMS FOR CRANE HOIST & THEIR SPEED

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WIRING DIAGRAMS FOR EOT CRANE PUSH BUTTONS

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TESTING AND MAINTENANCE

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• Three types of tests are required for cranes,
namely,
• Proof load tests
• Rated load tests
• Operational tests
TESTING OF CRANE

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Overhead bridge crane basic components

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If two hoists are used simultaneously, the combined rated load of
hoists shall not exceed the rated load of the support structure
Multiple hoists are permitted on a single support structure

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The proof load tests and operational tests shall be performed prior to first
use for new cranes, or for existing cranes that have had modifications or
alterations performed to components in the load path.
This applies only to those components directly involved with the lifting or
holding capability of a crane that has been repaired or altered.
Repairs or alterations to non-lifting, secondary lifting, or holding
components such as suspension assemblies, electrical system, crane cab,
etc., do not require a load test, although a functional check should be
performed to determine if the repairs or alternations are acceptable.
The rated load and operational tests shall be performed at least every 4
years. Cranes used frequently for critical lifts shall be load tested annually.

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Cranes used infrequently for critical lifts shall be load tested
before the critical lift if it has been more than a year since the
last test. If a crane is upgraded (increased lifting capacity), a
proof load test and an operational test shall be performed based
on the upgraded rating.
An inspection of the crane and lifting components shall be
performed after each load test and prior to the crane being
released for service to ensure there is no damage.
This inspection may include Nondestructive Evaluation (NDE) of
components that are suspected to be cracked or otherwise
affected by the test. The rated load test requirement may be
fulfilled by a concurrently performed proof load test.

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Proof Load Test
Before first use and after installation, all new, extensively
repaired, extensively modified, or altered cranes shall undergo a
proof load test with a dummy load as close as possible to, but not
exceeding 1.25 times the rated capacity of the crane.
A proof load test also should be performed when there is a
question in design or previous testing. The load shall be lifted
slowly and in an area where minimal damage will occur if the
crane fails.
The load rating of the crane shall be clearly marked to be legible
from the operator’s or usurer’s position and shall not be more
than the proof test weight divided by 1.25.

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Rated Load Test
Each crane shall be tested at least once every 4 years
with a dummy load equal to the crane’s rated capacity.
Cranes used frequently for critical lifts shall be load
tested at least once per year.
Cranes used infrequently for critical lifts shall be load
tested before the critical lift if it has been more than a
year since the last test. The acceptable tolerance for
rated load test accuracy is +5/-0 percent unless
otherwise specified by design.

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(a) New, reinstalled, altered, repaired, and
modified cranes shall be tested by a designated
person prior to initial use to ensure compliance.
(b) Tests shall include, as applicable, the following
functions:
(1) lifting and lowering
(2) trolley travel
(3) bridge travel
(4) hoist-limit devices
Operational Tests

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5) travel-limiting devices
(6) locking and indicating devices, if provided
(c) Operational testing of altered, repaired, and
modified cranes may be limited to the functions
affected by the alteration, repair, or modification,
as determined by a qualified person.
All operational testing must be performed by a
Certified Crane Inspector

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Operational Test
Together with proof load and rated load tests, the
following shall be performed with a dummy rated load
unless otherwise specified.
Load hoisting, lowering at various speeds (maximum
safe movement up and down as determined by the
installation NASA Safety directorate and the
responsible engineering and operations/maintenance
organizations), and braking/holding mechanisms.

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 Holding brakes shall be tested to verify stopping
capabilities and demonstrate the ability to hold a
rated load.
 Trolley and bridge travel (maximum safe
movement in all directions with varying speeds
as determined by the installation NASA Safety
directorate and the responsible engineering and
operations/maintenance organizations).

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All limit switches, locking devices, emergency stop switches, and
other safety devices, excluding thermal overload and circuit
breakers.
The limit switch, emergency stop, and locking device tests except for
the final upper limit switch shall be performed with no load on the
hook at full speed.
The final upper limit switch can be tested by manually tripping the
switch and verifying that all hoist motion is precluded.
Cranes used for critical lifts are required to be equipped with at least
two means of braking (hoist), each capable of bringing a rated load
to zero speed and holding it.

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The operational test must demonstrate each brake’s ability to
stop and hold a rated load. This can be done in one of the
following ways:
• Each brake’s ability to hold shall be statically tested (under no
load) with 150 percent of the rated load hoisting torque at the
point of brake application.
• Alternately, each brake shall be tested for its ability to stop a
rated load moving at full speed in the down direction.
CAUTION: It must be possible to quickly reenergize the out-of-
circuit brake or provide other safety measures to perform this
test safely.

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Adjustments
Based upon the manufacturer’s documentation and/or
experience, adjustments shall be made to ensure that all
crane components function properly, paying particular
attention to:
• Brakes. (Appropriate precautions should be taken by
inspectors, repair personnel, and others who may be
potentially exposed to airborne dust fibers from any
asbestos friction materials present in crane braking
mechanisms.)
• Control system.

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Limit switches.
• The hoist initial upper limit switch shall be verified by
running the empty hook at full speed into the limit
switch. It is recommended that the switch be verified at
slow speed prior to adjustment.
• For cranes used for critical lifts, the final upper limit
switch shall be independently verified and adjusted as
described above at installation and after modifications
that could affect switch operation. The switch can be
tested periodically by manually tripping it and verifying
that all hoist motion is precluded.

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INSPECTION
Daily and periodic safety inspections shall be
performed on all cranes and crane accessories.
Inadequacies discovered during an inspection shall be
documented and, if determined to be a hazard,
corrected prior to further use.
Inspections shall be made by qualified designated
personnel according to approved technical operating
procedures.

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i. Initial Inspection. New, reinstalled, altered, repaired,
and modified cranes shall be inspected by a
designated person prior to initial use to verify
compliance with applicable provisions of ASME B30.2.
• Inspection of altered, repaired, and modified
cranes may be limited to the provisions affected by
the alteration, repair, or modification, as
determined by a qualified person.
Inspection Classification

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ii. Inspection procedure for cranes in regular service is
divided into two general classifications based upon the
intervals at which inspection should be performed.
The intervals in turn are dependent upon the nature of
the critical components of the crane and the degree of
their exposure to wear, deterioration, or malfunction.
The two general classifications are designated as
frequent and periodic, with respective intervals
between inspection defined as follows:

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(1) Frequent Inspection. Visual examinations by the operator or
other designated personnel with records not required, as follows:
(a) normal service - monthly
(b) heavy service - weekly to monthly
(c) severe service - daily to weekly
(2) Periodic Inspection. Visual inspection of the equipment in
place by a designated person making records of apparent
external conditions to provide the basis for a continuing
evaluation, as follows:
• (a) normal service - yearly
• (b) heavy service - yearly
• (c) severe service – quarterly

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(a) The following precautions shall be taken before performing
maintenance on a crane:
(1) The crane shall be moved to a location where it will cause the
least interference with other cranes and operations in the area.
(2) If a load is attached to the crane, it shall be landed.
(3) All controllers shall be placed in the off position.
(4) A lockout/tagout procedure shall be performed.
(5) Warning signs and barriers shall be utilized on the floor beneath
the crane where overhead maintenance work creates a hazard
Maintenance Procedure

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(6) A guard or barrier shall be installed between
adjacent runways for the length of any established
work area to prevent contact between persons
performing maintenance and a crane on the adjacent
runway.
(b) The following precautions shall be taken before
performing maintenance on a crane runway, the
runway support structure, the runway conductor
system, or the areas of the building in the path of
travel of the crane bridge or trolley:

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(1) A lockout/tagout procedure shall be performed
(2) Warning signs and barriers shall be utilized on the
floor beneath the area where overhead maintenance
work creates a hazard
(3) A guard or barrier shall be installed between
adjacent runways for the length of any established
work area to prevent contact between persons
performing maintenance and a crane on the adjacent
runway.

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Runway and rail components

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(c) Only designated persons shall work on energized
equipment.
(d) After maintenance work is completed and before
restoring the crane to normal operation
(1) guards shall be reinstalled
(2) safety devices shall be reactivated
(3) replaced parts and loose material shall be removed
(4) maintenance equipment shall be removed

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(5) Warning signs and barriers shall be utilized on
the floor beneath the crane where overhead
maintenance work creates a hazard.
(6) If the runway remains energized, stops or a
signalperson(s), located full-time at a visual
vantage point for observing the approach of an
active crane(s), shall be provided to prohibit
contact by the active crane(s) with the idle crane,
with persons performing maintenance, and with
equipment used in performing the maintenance

Electric Overhead cranes

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