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Motor Control Centers
Motor control centers are often installed in
applications exceeding 1000 meters (3,280 ft)
above sea level. Due to the lower air density
and heat transfer capacity at elevated altitudes,
the physical properties such as dielectric
strength, load capacity of the motor control
centers, conductors and motors, as well as the
tripping characteristics of thermal relays may
require modification.
Paschen’s Law describes the breakdown
voltage of parallel plates in a gas as a function
of pressure and gap distance. In other words,
at a lower pressure (higher altitudes) it takes
less voltage to cross a given distance which
increases the chance for electrical arcs. To
compensate for this, it is recommended that
the operational voltage be de-rated for
altitudes exceeding 2,000 meters (6,600 ft).
In addition, the rated thermal current should
also be reduced because of the decreased
Altitude guideline
www.usa.siemens.com/mcc
thermal efficiency of lower density (high
altitude) air.
Siemens tiastarTM Motor Control Centers
(MCC) are designed and built to operate up
to 2000 meters above sea level without any
modifications. Siemens MCC components
are designed and manufactured to provide
excellent insulation and arc flash protection
for bus components, in addition to having a
high thermal efficiency. Using creative design
and engineering, Siemens MCC’s can operate
safely and reliably at altitudes up to 5,000
meters (16,400 ft) above sea level.
The purpose of this document is to provide
guidelines and specifications for the electrical
components used in Siemens tiastar Motor
Control Centers. These guidelines and
specifications are valid for motor control centers
operated up to 5,000 meters above sea level.
Component guidelines
Altitude (m)
2000
3000
De-rating
Voltage
Motor Control Center
Std. Aluminum and Copper 65°C rise
horizontal bus
Current
Voltage
4000
Current
Voltage
5000
Current
Voltage
Current
Requires enhanced Copper 50°C rise
horizontal bus
Motor Control Center
(MCC Bus & Enclosure)
600V
100%
480V
100%
480V
100%
480V
100%
Breakers
600V
100%
480V
97%
480V
94%
480V
91%
Starters
Innova
600V
100%
480V
97%
480V
94%
480V
91%
Sirius
600V
94%
600V
90%
480V
80%
480V
70%
Soft Starters
3RW40
460V
89%
460V
75%
460V
70%
460V
63%
3RW44
460V
92%
460V
85%
460V
78%
460V
70%
Drives
MM440 frame (FXGX)
100%
100%
90%
90%
77%
85%
—
—
MM440 frame (A-F)
100%
90%
90%
85%
77%
80%
—
—
6SE70
100%
90%
87.5%
84.5%
75%
80%
—
—
Siemens Industry, Inc.
Industry Automation Division
3333 Old Milton Parkway
Alpharetta, GA 30005
1-800-964-4114
[email protected]
www.usa.siemens.com/mcc
Subject to change without prior notice.
©2010 Siemens Industry, Inc.
The information provided in this brochure contains merely
general descriptions or characteristics of performance
which in case of actual use do not always apply as described
or which may change as a result of further development
of the products. An obligation to provide the respective
characteristics shall only exist if expressly agreed in the
terms of contract.
All product designations may be trademarks or product
names of Siemens AG or supplier companies whose use by
third parties for their own purposes could violate the rights
of the owners.