Rockwell Automation 284 ArmorStart User Manual - Manual (Page 434)

E-2 Group Motor Installations
Group motor installations using the ArmorStart in distributed control
applications will be largely dictated by the required motor Hp, their
locations and the practical concerns of wire-cable routing on the
equipment. It should be noted that Group motor installation are
designed to use the actual motor Hp and current ratings in NEC Table
430.250 and not the ArmorStart controller’s rating. This allows for
the possible standardization of ArmorStart controllers in an
installation. An application can be designed using 5 Hp controllers for
all motors between say 5 and 2 Hp and 1 Hp controllers for motors 1
Hp and less without having to oversize the wiring and short circuit
protection that would result from using the larger ArmorStart
controller’s rating.
In the case of using the Bulletin 284 VFD-ArmorStart the actual full-
load current of the motor needs to multiplied by the ratio of the
drive’s ratio of rated input current to output current to arrive at the
actual full-load current. For example, in the case of a 2 Hp VFD-
ArmorStart being used to control a 1 Hp 2.1 A @ 460 V motor, the
full-load amperes to be used for the Group motor calculation would
be the 2 Hp VFD-ArmorStart’s (Rated Input Current / Rated Output
Current) x 1 Hp motor’s rated full-load current; (5.7 A / 4.0 A)2.1 A =
3.0 A.
The following is a group motor example calculation for a 460 V
distributed application that requires two 10 Hp DOL-ArmorStart
controlling 10 Hp and 5 Hp motors and four 2 Hp VFD-ArmorStarts
controlling one 2 Hp motor and three 1 Hp motors. From NEC Table
430.250 the full-load current of the respective motors are:
Motor Hp Motor FLC (A)
10 14
5 7.6
2 3.4
1 2.1
1 2.1
1 2.1