Emerson EVH Series Installation Manual page 50

In the OFF position, the VFD Keypad control is disabled and the motor cannot be started from any means. This position also
removes the RUN ENABLE input to the VFD (DigIn2). In the Bypass position, the VFD Keypad control is disabled and the
motor started immediately in Bypass. This position also removes the RUN ENABLE input to the VFD (DigIn2). In the VFD
position, the VFD control is enabled and the motor can be started from keypad in either the Hand or Auto methods. This
position applies the RUN ENABLE input to the VFD (DigIn2).
Motor overload protection types
For bypass designs, the motor overload protection is provided by different methods depending on the input disconnect type
provided. It could be a Circuit Breaker/Disconnect or Type E CMC. Setting the Motor overload level and the OL trip/function is
dependent on the type of overload protection that senses the overload.
Circuit Breaker or Disconnect
Motor protection is provided by the following depending on the mode:
A bimetallic overload relay provides the overload protection when in running in the bypass mode and the VFD logic provides
the overload protection when the motor is running on the VFD.
Type E (CMC)
Motor protection is provided by the following depending on the mode:
The CMC input device provides the motor overload protection when in running in the bypass mode and the VFD logic
provides the overload protection when the motor is running on the VFD.
Note: The VFD logic provides the overload protection when the motor is running on the VFD.
Note: For Type E Disconnect designs, CMC overload protection is also active when running on the VFD mode, but the VFD
OL logic is more accurate and is the primary method of protection due to the nature of VFD output waveform.
Motor overload operation
D
epending the design and BCP, there are serval different ways a motor overload can be sensed.
Sensed by the bimetallic overload relay
The OL trip level is set by the overload relay using the dial set to the motor FLA. The OL relay is designed to protect the
motor at Class 10 protection. Some larger hp units may use CT base overloads, which provide Class 30.
When an overload occurs, the 24 V control circuit power is removed via the NC overload relay contact (95-96) (see
schematic). Both the VFD (M) and Bypass (B) contactors are disabled.
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