User`s manual

24
ELECTRIC COMPONENTS
MOTORS
The different types of motor on cranes and hoists are all provided with six-stud terminal boards.
Single-speed motors have terminal boards fitted for star or delta connections. Double-speed motors are fitted only for the nominal
voltage required; three terminals are used for low speeds and the other for high speeds.
Terminal arrangement is given on each motor rating plate.
Before carrying out crane tests make sure that the rating plate voltage, referring to the motor connections, is the same as your mains.
Motors do not require any special maintenance and bearings are pre-greased for a very long service period.
To ensure cooling make sure that the casing is kept clean and as free of dust as possible. Also make sure that couplings attached to
parts projecting from the shaft are well secured and not loose; if loose, repeat keying immediately (change fiat-key or half-coupling).
It must be remembered that if the motor does not start with a suspended load perhaps the power supply voltage is lower than the
nominal voltage; starting with a full suspended load is only possible when the voltage at the motor terminals on take-off is no lower
than 5% the one on the rating plate, unless otherwise specified.
AUTOMATIC LIMIT SWITCHES
Automatic limit switches are emergency devices, therefore they must not be used in normal service conditions.
If they are needed for normal conditions additional limit switches will be installed in such a way that they work before the emergency
ones.
The limit switches which are normally installed on the three movements of the crane are auxiliary switches; they function on the low
voltage current so as to open the corresponding control contactor.
On request, for particularly demanding service, it is possible to install power limit switches which directly cut off two or three phases at
the motor power supply.
However, these devices must be released by hand.
TROLLEY TRAVELING AND BRIDGE SLIDING AUTOMATIC SWITCHES
These switches may be either roller type or "double-lyre" shaped. In both cases, in order to alter the bridge or Trolley approach
operations, the fixed catches must be moved without touching the switch.
The trolley stop distance is set on construction, while the crane stop catch has to be installed during assembly following the same
procedure as for the trolley.
The roller type limit switches for the bridge require rather long shoes (at least twice the braking distance) while the double-"lyre" limit
stop switches a catch to act on the "lyre" is needed.
Limit switches are devices, that should not be abused and frequently inspected.
ANTI-COLLISION
When two machines are running along the same railways, automatic stop devices must be installed to prevent collision when the
safety distance is exceeded.
These devices are placed in such a way that the two machines will not collide even at maximum speed. The brakes must be set for
short-distance braking and kept under constant check.
TROLLEY FEEDING LINE
For the power supply of moving equipment, round or fiat form flexible cable in loop arrangement are normally used, thus allowing the
cable to stretch along a section parallel to the hoist trolley or crane bridge.
The loops are supported by saddles which are attached to trolleys sliding along their raceway.
The flexible cables can be either single or multiple according to service requirements as it is possible to have low voltage conductors
or mains voltage conductors the main switch must be in the "OFF" position before any repairs or maintenance are carried out.
No maintenance is required for this type of line apart from inspection of the trolleys to check they slide properly, and constant checking
of the screw which holds the joints and the suspensions.
Special care must be taken during the assembly of the track; flush the joints so as to avoid the loop feeders jamming and the resulting
tearing of the cables.
The conductors are sheathed in PVC. thus allowing a service temperature range of -20° to +70°C, unless o therwise specified.
An alternative to festooned lines which is often used is the cable supporting chain, which is supported by raceways fitted on the crane
frame.