Rockwell Automation Publication 290E-UM001B-EN-P - June 2012 183
Applying More Than One ArmorStart LT Motor Controller in a Single Branch Circuit on Industrial Machinery Appendix A
Figure 59 - UL508C Variable-Frequency AC Drive Motor Controller Evaluation
Maximum Fuse Ampere
Rating According to
7.2.10.4(1) and 7.2.10.4(2)
This section uses Figure 60 to explain the requirements from 7.2.10.4(1) and
7.2.10.4(2) that are relevant to, and permit, the multiple-motor branch circuit
of Figure 58
.
The following is the complete text of 7.2.10.4(1) and 7.2.10.4(2) and an
abbreviated version of Tab le 3 0
from the 2012 Edition of NFPA 79. The table
is abbreviated to cover the size of conductors that are generally relevant to the
ArmorStart LT motor controllers.
Complete Text -
“7.2.10.4 Two or more motors or one or more motor(s) and other load(s), and
their control equipment shall be permitted to be connected to a single branch
circuit where short-circuit and ground-fault protection is provided by a single
inverse time circuit breaker or a single set of fuses, provided the following
conditions under (1) and either (2) or (3) are met:
(1) Each motor controller and overload device is either listed for group
installation with specified maximum branch-circuit protection or selected such
that the ampere rating of the motor branch short-circuit and ground-fault
protective device does not exceed that permitted by 7.2.10.1 for that individual
motor controller or overload device and corresponding motor load.
(2) The rating or setting of the branch short-circuit and ground-fault
protection device does not exceed the values in Tab le 3 0
for the smallest
conductor in the circuit.”
(3) …(not considered in this appendix)
UL 508C –
test with 6
ampere max
Manufacturer’s choice -
Reduce rating for test
to 45 A
Max = 400% * Rated Output Current
= 400% * 1.5 A = 6 A
Max rating for 10 AWG
= 250 A
Max permitted
rating for test
fuse based on
Rated Output
Current
Max permitted rating
for test fuse based
on maximum size
of power conductors
Maximum
conductor size
= 10 AWG
Maximum
conductor size
= 10 AWG
½ HP Motor
Controller
Bulletin 294
½ HP Motor
Controller
Rated Output
Current = 1.5 A
6A fuse max
Suitable for
motor group
installation
Rated Output
Current = 1.5 A
45 A fuse max
MotorMotor
Short-Circuit Test Circuit Short-Circuit Test Circuit
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