Page 99 - Electromechanical Devices and Components Illustrated Sourcebook

Chapter 4 Electrical Controls 61

Motor Starter
(Main) MOTOR
Power
RESET 220/240 VAC COIL (240/480 VAC)
CONTROLLER
Control
Transformer
460/480 VAC
CONTACTOR
Delta 20 HP / 30 AMP
Contactor 24 VAC COIL On/Off
115/120 VAC
Switch
On/Off
Lamp
CONTACTOR
Wye 20 HP / 30 AMP
Contactor 24 VAC COIL .4 .5 .6
.3 .7
.2 .8
.1 .9
0 1 Chassis Ground
Seconds
Delay On Relay

Enclosure
Internal Panel

Motor
Figure 4-73 Delta/Wye Motor Controller

When the motor is turned on, the starter connects the motor in
a Wye configuration which will produce lower torque charac- Main Contactor Element Fuses
teristics. After a predetermined period of time, the Wye con- Main Fuses Element
Primary Contactors
tactor opens and the Delta contactor closes. The controller Disconnect
remains in a delta configuration until the motor is restarted. 240/480 VAC Element 1
Three Phase
Figures 4-72 and 4-73 show a basic Delta/Wye motor starter
C C
configuration.
L Indicator Lamps
Large three-phase resistive furnaces are typically controlled
with contactors such as those shown in Figures 4-74 and 4-75. Element 2
These furnaces use arrays of heating elements that are inde-
C
pendently switched via contactors. The control circuit for the
contactors is typically connected to a sector thermostat as L
shown in the schematic. Element 3

C
Relays L

Relays are similar to contactors, except that they are generally Sector Thermostat Element 4
designed to emulate higher-level switch functions. Relays are
C
normally multipole, double throw devices and are usually
L
designed for low-current switching. Relays are used exten-
Power Switch
sively for control applications and are found in nearly every
electromechanical appliance manufactured. Control Circuit Fuse
Control Transformer
Figure 4-76 shows a single-pole, double throw knife Transformer Fuses
switch relay. Take particular notice of its similarity to the Figure 4-74 Electric Furnace Controller Schematic