The size of the overload device on a motor magnetic would be determined by the starting current of the motor.
A three phase motor magnetic starter must have an overload heater in each phase.
Magnetic overloads are made adjustable by physically moving the armature in or out of the magnetic field produced by the motor current.
A standard motor magnetic consists of a contactor and an overload device.
Holding contacts are connected:
A) directly in series with the stop button
B) in parallel with the operating coil
C) in series with the start button
D) in parallel with the start button
E) both "B" and "D" apply
in parallel with the start button
Magnetic overloads are said to be:
A) heat dependant
B) time lag
D) none of the above
The purpose of the holding contacts on a motor magnetic is to keep the coil energized after the start button has been released.
When the armature of a motor magnetic is pushed in by hand, a continuity test between terminals 2 and 3 shows zero ohms. This is an expected reading.
The rule in Section 28 of the C.E.C used to determine the AMPACITY of overload heaters for motor controllers would be:
A) 28 - 304
B) 28 - 302
C) 28 - 306
D) 28 - 308
28 - 306
The NEMA numbering for the terminals of the holding contacts are 1 and 2.
The two basic principles of operation used for overload protection devices in a motor circuit are thermal and electromagnetic.
It is possible to order a bi-metal thermal overload device with ambient temperature compensation.
According to the C.E.C., only two overload heaters are required for a three phase motor.
"Holding" contacts are used as a by-pass of the:
A) operating coil
B) start button
C) motor contacts
D) overload heaters
E) more than one of the above apply
A motor magnetic is a:
A) relay with overload devices
C) contactor with overload devices
D) both "A" and "B" apply
E) all of the above apply
contactor with overload devices
There are two types of thermal overload devices. These are the bi-metal and the melting alloy type.
When a motor magnetic starter is used on a higher voltage the hp rating of the starter is increased.
When the armature of a motor magnetic is held in the closed position, a continuity test between L(2) and T(2) indicates zero ohms. This is most likely a sign that:
A) coil needs replacing
B) everything is normal
C) the wiring in the starter is faulty
D) the contacts are faulty
E) the overload heater is burnt out
everything is normal
When the armature of a motor magnetic is held in the closed position, a continuity test between L(1) and T(1) indicates an open circuit. This is a sign that:
A) the wiring in the starter is faulty
B) the overload heater is burnt out
C) everything is normal
D) the contacts are faulty
E) coil needs replacing
the overload heater is burnt out
The NEMA numbering for the terminals of the holding contacts are 2 and 3.
Construction of Magnetic Motor Starters/Overload Devices 030205e