Rockwell Automation 294D ArmorStart LT Distributed Motor Controller DeviceNet Version - User Manual User Manual
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Rockwell Automation Publication 290D-UM001A-EN-P - June 2012
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Applying More Than One ArmorStart LT Motor Controller in a Single Branch Circuit on Industrial Machinery
Appendix A
1. Requirement One: Controller Ratings
— The motor controllers and
overload relays must be listed for group installation with specified maximum
branch-circuit protection.
Text:
“7.2.10.4(1) Each motor controller and overload device is… listed for group
installation with specified maximum branch-circuit protection…”
Analysis:
To apply the ArmorStart LT motor controllers in the multiple-motor
branch circuit shown in
, 7.2.10.4(1) must be satisfied; each controller
must be listed for group installation with specified maximum branch-circuit
protection. The UL listing for each ArmorStart LT motor controller confirms
that it – including its integral overload relay and motor disconnecting means — is
suitable for motor group installation with specified fuses, satisfying 7.2.10.4(1).
The Bulletin 290D and 291D controllers are listed for group installation
according to UL 508, Industrial Control Equipment. The Bulletin 294D
controllers are listed for group installation according to UL 508C, Power
Conversion Equipment.
Referring to
(a) indicates the markings on the nameplate that satisfy
7.2.10.4(1). The marking “Suitable for Motor Group Installation” satisfies the
requirement to be listed for group installation. The ratings located beneath the
description “Max. Ratings” are the specified maximum branch circuit protection.
The (a) beside the fuse(s) indicates that the maximum protection specified on the
nameplate applies to these fuse(s).
2. Requirement Two: Conductor Short-circuit and Ground-Fault
Protection
— The fuse must protect the conductors for short-circuit faults
and ground faults.
Text:
“7.2.10.4(2) The rating or setting of the branch short-circuit and ground-
fault protection device does not exceed the values in
for the smallest
conductor in the circuit.”
Analysis:
Referring to
, 7.2.10.4(2) must be satisfied. The fuse, as
indicated by the description in
(a), is the branch short-circuit and
ground-fault protection device. The word circuit means the branch circuit.
The conductors of the branch circuit start at the load side of the fuses and end
at the input to the motor, including the conductors between the motor
controllers and the motor. The smallest conductor in the circuit is any one
of the 14 AWG conductors that supply each controller and motor. The note
at (b) indicates the conductor protection is based on the smallest conductor,
14 AWG. Referring to
a 14 AWG conductor may be used in a circuit
that is protected by a fuse of any class having a rating of 60 amperes or less (c).
Therefore, selecting a fuse of any class with a maximum rating of 60 amperes
satisfies the conductor protection requirement of 7.2.10.4(2).
Supplementary Note 1:
The value specified in
is the maximum rating
of fuse that 7.2.10.4(2) permits to protect that size of conductor. The rating of
the fuse may be set to the maximum value given by
for the smallest
conductor without further justification. However, if any controller, or other
component, has a maximum rating of fuse that is less than the
value, the