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"Before
you buy - A motor purchasing checklist"
With
trilingual summary
Once the
rating and availability of a motor has been decided upon through study of the
application requirements, the purchaser will benefit from reviewing a number of
common alternatives that will influence the overall economics of the
installation. Unless a user is certain that a completely standard motor will be
suitable, careful attention should be given to special features, accessories
(such as oil mist lubrication or space heaters), and a specification detailing
what is required. That should include a request for factory test data that may
be desired as a benchmark for condition monitoring in service.
A useful
checklist includes such items as:
1,
Voltage rating. Standard motor ratings are normally slightly less than the
standard power supply system ratings, to allow for circuit voltage drop. Avoid a
mismatch greater than 10 percent between motor nameplate voltage and the extreme
variation expected on the system.
2.
Enclosure. This must be appropriate for the environment, but the
totally-enclosed machine cannot be considered watertight or dust-tight, and no
motor should be expected to provide such capability.
3.
Interchangeability. Although industry standards may dictate use of the same
major dimensions for motors of different manufacturer, some dimensions can vary
enough to cause mounting conflicts.
4.
Starting duty: Whether a motor can safely start its load, and how often, can
only be confirmed by the motor designer, given full knowledge of the load
characteristics. The motor user cannot expct to make that calculation.
5.
Variable speed: If a variable-frequency drive is to be used, that needs to be
made clear when the motor is ordered. The best practice is to purchase both
motor and power supply from the same vendor, to assure single-source
responsibility for the drive.
6. Cost.
Not only price, but long-term energy cost needs careful study. If a new motor is
to replace an existing one, removal and replacement costs are also important.
From “Before
you buy - A motor purchasing checklist,"
published in the
Electrical Apparatus August 2007 issue
. Visit our online webstore to
order
copies. © 2007
Barks Publications, Inc. All Rights Reserved.
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