SPX Cooling Technologies MARLEY CLASS 800 - Manual (Page 14)

14
Temperature Control and Energy
Management
Excessive cycling of motors causes overheating of the windings
and ultimate failure of the motor. The total amount of starting time
(period of high inrush current) should not exceed 30 seconds per
hour. On fans 20 feet diameter and smaller, this may allow 4 or 5
starts per hour. On larger fans, 1 or 2 starts per hour may be the
limit. Determine the number of seconds it takes your fan to get to
full-speed (by observation) and divide that number into 30 to obtain
the recommended maximum number of starts per hour. Two-speed
motors cycling between half and full speeds permit a commensurately
greater number of control cycles.
Variable frequency drives, of course, provide the ultimate in both temperature
control and energy management and can be easily retrofitted to your system.
Please discuss this with your Marley representative.
Caution