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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.