Page 247 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS

Motor control centers (Fig 31)
In many commercial and industrial applications, quite a few electric motors are required, and it is often desirable
to control some or all of the motors from a central location. The apparatus designed for this function is the motor
control center (MCC).
Motor control centers are simply physical groupings of combination starters in one assembly. A combination
starter is a single enclosure containing the motor starter, fuses or circuit breaker, and a device for disconnecting
power. Other devices associated with the motor, such as pushbuttons and indicator lights, may also be included.

Fig 31

Advantages
Some of the advantages of using motor control centers are:

1 Ruggedness and reliability
2 Reduced time needed for installation and startup
3 Space saving design
4 Excellent component selection
5 Simplicity in adding special components

6 Ease of future modifications.
Drawing of control panel
Types of drawing
We use drawings to convey the information about a piece of equipment in a form which all those involved in its
production, installation and service will under¬stand. To make this possible, standard drawing conventions have
been adopted by most companies.
The information we need to be able to assemble the equipment will be only one item in the set of drawings and
schedules which make up the complete design.
Circuit diagram (Fig 32)
This shows how the electrical components are con¬nected together and uses:

• Symbols to represent the components;
• Lines to represent the functional conductors or wires which connect them together.
A circuit drawing is derived from a block or functional diagram. It does not generally bear any relationship to the
physical shape, size or layout of the parts and although you could wire up an assembly from the information given
in it, they are usually intended to show the detail of how an electrical circuit works.

234

CITS : Power - Electrician & Wireman - Lesson 93-100