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FAQ's - Drives
Adjustable Speed Drives Frequently Asked Questions
The following information is intended to answer commonly asked questions about AC variable
frequency drives (VFDs).
Installation
Programming
Diagnostic
Application
Installation Questions:
How much space is required around the VFD?
Depending on the VFD series that is being used, maintain the following spacing around each VFD:
Micro Series: 2 inches below 5 HP; 4 inches for 5-25 HP; 6 inches for 25-60 HP; 8 inches above 60
HP.SM Plus Series & SM-Series: 1 inch on each side and 2 inches on the top and bottom for 10 HP
and below; 1inch on each side and 4 inches on the top and bottom for 15-25 HP.
How are enclosures sized if someone wants to mount a drive inside a panel?
Enclosure manufactures typically determine the size of enclosure needed based on entering
some data into a computer program they can access for the purpose. They need to know the ambient
temperature that the drive can operate in (50C for NEMA 1, 40C for NEMA 4/12) and how much heat
is dissipated by the drive. Use the following formula for a guideline only:Watts Dissipated = (HP x
750 x .04) climate space /EFF OF MOTOR. Consult the manual for further information (section 5.0).
Can VFDs be mounted above one another?
It is not recommended to mount VFDs above other VFDs or other heat producing equipment that
would impede the cooling of the VFD, unless sufficient space and additional cooling (fans, blowers, air
conditioners, etc.) are provided.
What precautions must be taken when running the VFD’s power conductors and control
wires?
When running the power and control wires, the following guidelines should be followed:
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Install the AC input power wiring in its own rigid steel conduit.
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Install the output motor leads in their own rigid steel conduit.
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Install the control wiring in its own rigid steel conduit. Low voltage DC control wiring and 120
Vac control wiring should be run in separate conduits.
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Make sure that all grounds are tightly connected, and properly earth grounded.
NOTE: If multiple VFDs are mounted near each other, the input power wiring for each VFD can be run
in the one conduit, and the control wiring for each VFD can be run in a second conduit, but each set
of motor leads MUST be in a separate conduit. However, if one VFD is used to run multiple motors,
the output wiring for all of the motors can be run in the same conduit.
Is the VFD phase sensitive?
The VFD’s input is insensitive to the phase sequence of the input voltage. Therefore, changing the
input phase sequence will not change the rotation of the motor. However, changing the phase
sequence of the VFD’s output will change the motor rotation. When applying a VFD, the motor
Catalog Number
ex.110088
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LEESON Electric Corporation - www.leeson.com
10/15/2009
http://www.leeson.com/TechnicalInformation/faqdrives.html
