Rockwell Automation Publication 750-QS100B-EN-P - August 2020 31
Step 5: Enter Motor Data
Enter Motor Overload Hertz
The motor OL Hertz is typically not on the motor nameplate. This information is available from the motor
manufacturer data sheets. Motor OL Hertz is the fundamental frequency below which the motor cannot deliver rated
torque continuously without the possibility of overheating. This is sometimes referred to as the 'speed turn-down ratio'.
Self-cooled motors with Totally Enclosed Non-Ventilated (TENV) enclosures, Drip Proof Guarded (DPG) enclosures,
and Totally Enclosed Fan Cooled (TEFC) enclosures, have shaft driven cooling fans. These fans cannot produce the
volume and pressure of cooling air that is required to produce rated motor torque continuously, without the motor
overheating when operated below the minimum speed turn-down frequency. Motors with separately powered cooling
fans, such as those with Totally Enclosed Blower Cooled (TEBC) enclosures, and Drip Proof Guarded Force Ventilated
(DPG-FV) enclosures, can typically be operated to zero speed without overload Hertz derating.
For example, a 60 Hz base speed TEFC motor with 4:1 speed turndown ratio can only produce rated torque
continuously down to 60 Hz / 4 = 15 Hz. In this example, parameter 10:204 [Mtr OL Hertz] would be set to 15 Hz.
Another example is a 60 Hz base speed TEBC blower cooled motor with a 1000:1 speed turndown ratio. In this case,
parameter 10:204 [Mtr OL Hertz] would be set to 60 Hz / 1000 = 0.06 Hz or 0 Hz.
Setting parameter 10:204 [Mtr OL Hertz] does not affect the drives capability to deliver motor current or limit output
current in any way. Parameter 10:204 only sets the threshold where the motor overload counter begins to increment.
1. Navigate to parameter 10:204 [Mtr OL Hertz]. Press the EDIT soft key.
2. Edit the overload threshold frequency in Hertz, based on the data collected in Ta b le 1 on p a ge 8
and the previous
calculations. Press the ENTER soft key.
Enter Motor Protection Class
This parameter is available in firmware revision 10 and higher. The motor protection class, or trip class, defines the
length of time it takes to trip the system in an overload condition. The Motor Protection Class parameter can have a
value between 1 and 60. This value is the maximum number of seconds until the motor trips off when it is in an overload
condition. An overload condition is defined as the current being over 600% of the maximum thermal current rating (or
600% of the actual dial setting on adjustable overloads). So if the motor current is over 600% of the maximum thermal
current rating, and the motor protection class is 60, the motor will trip in 60 seconds or less.
The default value for Motor Protection Class is 11. Many industrial loads, particularly high inertia loads, require Class
30. Use a protection class appropriate for your application, considering motor thermal curves, operating conditions, and
inertia of the load. For more information on motor protection class, refer to the Low Voltage Motor Protection White
Paper, publication 193-WP008
. To set Motor Protection Class, use the following procedure.
1. Navigate to parameter 10:209 [Mtr Protn Class]. Press the EDIT soft key.
2. Enter the Motor Protection Class that is recorded in Ta ble 1 on p a ge 8
. Press the ENTER soft key.
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