User Manual Owner's manual

Rockwell Automation Publication 280E-UM001B-EN-P - July 2012 269
Applying More Than One ArmorStart Motor Controller in a Single Branch Circuit on Industrial Machinery Appendix A
Figure 97 - ArmorStart LT NFPA 79 Multi-Motor Branch Circuit
Explanatory Example
The example addresses the overcurrent protection of the conductors, controllers
and motors. Protection for three overcurrent conditions is considered: motor
running overloads, short-circuit (line-to-line) faults, and ground-faults (line-to-
ground). The short-circuit fault and ground-fault protection is governed by
7.2.10.4(1) and 7.2.10.4(2) and explained in Requirements 1,2 and 3 and
Figure 98
. The overload protection,explained in Requirement 4, is governed by
7.3.1 and 7.3.1.1. Overload coordination depends on each conductor having the
minimum ampacity given by 12.5.3 and 12.5.4. The method for determining this
minimum ampacity is explained in Requirement 5 and Figure 99
.
The example branch circuit is shown in Figure 98
and Figure 99. The circuit
topology consists of a set of 10 AWG conductors that supply multiple sets of 14
AWG conductors. Each set of 14 AWG conductors supply a controller and
motor. These conductor sizes are chosen to be the smallest conductors that have
sufficient ampacity, without derating, for the loads each must carry. All of the
wiring is customer-supplied, rather than the ArmorConnect Power Media,
because all controllers have the Conduit Entrance Gland Plate Option. Fuses
protect the branch circuit.
The example addresses five basic requirements that the motor controllers, fuses
and conductors must satisfy. The letters in the circles on Figure 98
and Figure 99
are referenced in the explanations as letters in parentheses. Ellipses points (…)
are used to replace NFPA 79 text that is not applicable to the multiple-motor
branch circuit shown in Figure 98
and Figure 99. Unless indicated, all text is
from NFPA 79.
d
f
e
c
e
b
“...a single set
of fuses…”
“The rating or setting of the branch short-circuit
and ground-fault protection device does
not exceed the values in Table 7.2.10.4
for the smallest conductor in the circuit.”
Branch circuit (shown as dotted lines) –
all of the conductors on the load side
of the single set of fuses
“...shall be permitted to be connected to a single branch circuit…”
* Each controller is listed for group installation with the same specied maximum protection
Markings that satisfy
7.2.10.4(1)
“... and their control
equipment … ”
“Two or more motors ...”
a
“Each motor controller
and overload device is ...
listed for group
installation with specied
maximum branch-circuit
protection…”
½ HP
Bulletin 294
2 HP
Bulletin 294
5 HP
Bulletin 291
5 HP
Bulletin 290
1 HP
Bulletin 294
Overload
Class 10
Overload
Class 10
Overload
Class 10/15/20
Overload
Class 10/15/20
Overload
Class 10
Nameplate* Nameplate* Nameplate* Nameplate* Nameplate*
1/2 HP
FLC =
1.1 A**
2 HP
FLC =
3.4 A**
5 HP
FLC =
7.6 A**
5 HP
FLC =
7.6 A**
1 HP
FLC =
2.1 A**
“Suitable for Motor Group Installation”
Max. Ratings
5 KA 10 KA
45A 45A*
Sym. Amps RMS
Fuse
* Type CC, J and T fuses only