Analysis of Motor Control Circuits: Seal-in and Latched/Unlatched

This assignment delves into the analysis of motor control circuits, focusing on two primary types: seal-in circuits and latched/unlatched circuits. The assignment begins by explaining the operational principles of a seal-in circuit, detailing how it maintains a continuous motor operation even after the start button is released, emphasizing the use of normally open contacts to achieve this functionality. The construction of a seal-in circuit is then described, highlighting the wiring configurations, including the use of a contactor relay and stop button, often illustrated through a ladder diagram. Subsequently, the assignment transitions to latched/unlatched circuits, explaining how the magnetic field generated by electrical currents controls the switching action of the circuit, and how a magnetic strip is used in between the coils. The construction of a latched/unlatched circuit is also discussed, emphasizing the wiring of normally open and normally closed contacts in series and parallel, again typically illustrated with a ladder diagram. The assignment concludes with a bibliography of relevant resources.

PHYSICS 1
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PHYSICS 2
There are two basic types of stop/start/retain relay control circuits for either an AC or DC
machine basically a Motor. These types are basically the seal in the circuit and the
latched/Unlatched circuit stop.
Seal in circuit
Operation of seal in Circuit
If the start ( which is a pushbutton in this case) is released or even pressed the signal there will
be a signal at a given time (momentarily) but after some time the signal will be lost (Herman,
2013). Therefore there is a need to latch the circuit so as to make the motor to operate
continuously even after the start button has been released. In this case the use of Relay (M)
normally open contact across the start push button in order to take care of the start signal after
releasing the start button. The seal in auxiliary (which is a Normally open contact / NO) of the
motor starter is connected in parallel to the start button so as to make the starter coil (M) become
energized immediately the start button is released (Bhattacharya, 2017). And when the start
pushbutton has pressed the coil of the Motor starter will be energized and the normally open
contact will hence become normally closed (NC).
Construction of the seal in circuit
Basically, the construction of this type of control circuit is actually through the wiring of the
device to make the circuit the way it supposed to be. Basically, the power from the mains
supply is a switch which is a NO will go to a contactor relay which will help in making even
after the pressed button has been released from the button. From the contactor relay, the stop

PHYSICS 3
button which is Normally closed (NC) is connected before the final connection to the motor
being controlled. Basically, this can be illustrated using a ladder diagram.
Latched/Unlatched circuit stop
Operation of the latched/Unlatched circuit stop
Immediately the electrical current enters into the coil, there will be the generation of the
magnetic field, this will again turn off when this latching relay operates. Since the magnetic strip
is suspended in between the two coils, it is hence a subject to their magnetic field (Denton,
2013). And as the circuit produces a pulse of electricity in the coils, it will push the switch from
one point to the other point. Therefore the strip stays in that point up to the time the coil gets a
magnetic pulse in the opposite direction making the switch to move back to the other terminal.
Construction of latched/ unlatched circuit stop
The construction of this type of control circuit is also based on the wiring to make the control
circuit. Basically, the normally open (NO) contact is connected to a motor which is latched. The
NO is should be in parallel to another stop switch which is a normally closed switch (NC)
(Hurlton, 2012). The NC is connected in series to an unlatched motor. Basically, this can be
illustrated using a ladder diagram.

PHYSICS 4
Bibliography
Bhattacharya, K., 2017. Control of Machines. 1st ed. New York: New Age International.
Denton, T., 2013. Automobile Electrical and Electronic Systems. 3rd ed. Hull: Routledge.
Herman, S., 2013. Industrial Motor Control. 3rd ed. Hull: Cengage Learning.
Hurlton, D., 2012. Electrical and motor control. 3rd ed. Chicago: CRC press.