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Grounding In the USA consult the National Electrical Code, Article 430 for information on grounding of motors and
generators, and Article 250 for general information on grounding. In making the ground connection, the
installer should make certain that there is a solid and permanent metallic connection between the ground
point, the motor or generator terminal housing, and the motor or generator frame. In non−USA locations
consult the appropriate national or local code applicable.
Motors with resilient cushion rings usually must be provided with a bonding conductor across the resilient
member. Some motors are supplied with the bonding conductor on the concealed side of the cushion ring
to protect the bond from damage. Motors with bonded cushion rings should usually be grounded at the
time of installation in accordance with the above recommendations for making ground connections. When
motors with bonded cushion rings are used in multimotor installations employing group fusing or group
protection, the bonding of the cushion ring should be checked to determine that it is adequate for the
rating of the branch circuit over current protective device being used.
There are applications where grounding the exterior parts of a motor or generator may result in greater
hazard by increasing the possibility of a person in the area simultaneously contacting ground and some
other nearby live electrical parts of other ungrounded electrical equipment. In portable equipment it is
difficult to be sure that a positive ground connection is maintained as the equipment is moved, and
providing a grounding conductor may lead to a false sense of security.
Select a motor starter and over current protection suitable for this motor and its application. Consult motor
starter application data as well as the National Electric Code and/or other applicable local codes.
Adjustable Frequency Power Inverters used to supply adjustable frequency power to induction motors
produce wave forms with lower order harmonics with voltage spikes superimposed. Turn−to−turn,
phase−to−phase, and ground insulation of stator windings are subject to the resulting dielectric stresses.
Suitable precautions should be taken in the design of these drive systems to minimize the magnitude of
these voltage spikes. Consult the drive instructions for maximum acceptable motor lead lengths, and
proper grounding.
Thermal Protection
Thermostat leads marked P1 & P2 must be connected in series with the stop button of the 3−wire pilot
circuit of the magnetic motor controller, so that the thermostat will open the circuit before dangerous
temperatures are reached. Thermostats are automatic reset for use in a normally closed circuit where the
thermostat is connected In series with the holding coil of the magnetic starter. Thermostats provide "Over
Temperature" Protection in accordance with NEMA MG 1−12.53. Thermostats do not provide winding
over temperature protection (locked rotor). It is suggested that over current protection be used in the
motor starter to ensure locked rotor protection.
Stop
Start
MN414
Figure 2-2 Thermal Protection Circuit
L1
L2
L3
GND
Starter
T1 T2 T3
GND
P2
Motor
P1
Volts
AC
110-120
AC Line
220-240
440-480
550-600
P1 & P2 N.C. Thermostat Leads (N.O. Contacts unacceptable to UL)
Starter Holding Coil
Holding Coil Contacts (N.O.)
Motor Power Cable Lead Color
Black
White
Polyphase
T1
T2
Single Phase
T1
T4
Continuous
Inrush
Amps
Amps
3.0
30
1.5
15
0.75
7.5
0.6
6.0
Red
Orange
Green
T3
-
Ground
TA
-
Ground
Installation & Operation 2−3
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