Permissible Loading Of Motor Control Centers - Siemens tiastar Instruction Manual

4.3 Permissible loading of
motor control centers
1. For motor control centers without main
overcurrent protective devices, the total
continuous load current through the horizontal
bus should not exceed the current rating of the
motor control center.
2. For motor control centers with a single main
overcurrent protective device, the total
continuous load current on the protective device
should not exceed 80 percent of its ampere
rating unless the device is rated to carry 100
percent of its ampere rating, in an enclosure.
3. For motor control centers with multiple main
overcurrent protective devices, the total
continuous current through the horizontal bus
should not exceed the current rating of the
motor control center. The total continuous load
current on each overcurrent protective device
should not exceed 80 percent of its ampere
rating unless the device is rated to carry 100
percent of its ampere rating, in an enclosure.
4. For branch-circuit overcurrent protective devices
in a motor control center, the total continuous
load current on the protective device should not
exceed 80 percent of its ampere rating unless the
device is rated to carry 100 percent of its ampere
rating, in an enclosure.
5. The maximum short-circuit current rating of the
entire motor control center is the smallest of the
following:
a. the rating of the bus structure, or
b. the lowest rating of the motor control units, or
c. the lowest rating of the feeder units.
This motor control center rating is clearly indicated
on the lead sheet located in the information packet.
tiastar™ Motor Control Centers Instruction Manual Operation
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