IT Altitude Considerations (Derating) - Application Note

AP03901002E For more information visit: www.cutler-hammer.eaton.com IT. Altitude Consideration s Application Note Electromechanical Contactors and Starters IT . Electromechanical Contactors and Starters are designed for operation at up to 6,562 feet (2000 m) altitude, when applied within their temperature and power ratings. This note provides guidance for those applications that require operation at altitudes in excess of 6,562 feet (2000 m). As altitude increases, the air density is reduced. The reduction in air density affects both the cooling and voltage breakdown of various electrical components. As a result, a derating factor must be applied to compensate for the lesser capabilities at higher altitudes. First, the current rating of the IT . Con- tactor or Starter is reduced because of the reduced cooling effect. Second, a derating factor is applied to the voltage . This derating factor is related to the voltage impulses present on the power system and the breakdown ratings of the components used within the contactor or starter. Since this is difficult to evaluate in a field situation, for simplification, a derating factor is applied to the operating voltage level to suggest the use of a higher utiliza- tion voltage (U e ) level. For IT . electromechanical products, the following derating factors are to be applied. Table 1. Derating — Altitudes above 6,562 feet (2000 m) Note: Interpolation between values is permitted. As an example of using the derating factors, an installation will be made at 11,483 feet (3,500 m) for which the application requires a 32 ampere contactor at 480 volts. Which IT. Contactor should be selected? In this situation, because the Altitude (ALT) is between tabulated values, the required current would be divided by an interpolated Current Factor (CF), and the voltage divided by an interpolated Voltage Factor (VF). Rated Current ³ (Required Current) / ((CF LOW – CF HIGH ) x (ALT REQ – ALT LOW ) / (ALT HIGH – ALT LOW ) + CF HIGH ). Rated Current ³ 32 / ((0.95 – 0.90) x (3500 – 3000) / (4000 – 3000) + 0.90). Rated Current ³ 32 / ((0.95 – 0.90) x (500 / 1000) + 0.90). Rated Current ³ 34.6 amperes. Rated Voltage ³ (Required Voltage) / ((VF LOW – VF HIGH ) x (ALT REQ – ALT LOW ) / (ALT HIGH – ALT LOW ) + VF HIGH ). Rated Voltage ³ 480 / ((0.87 – 0.77) x (3500 – 3000) / (4000 – 3000) + 0.77). Rated Voltage ³ 480 / ((0.87 – 0.77) x (500 / 1000) + 0.77). Rated Voltage ³ 585 volts. From the IT. Contactor catalog, an IEC E111C40X3N or NEMA N111DS2X3N would be selected. This 40 ampere IEC Contactor or 45 ampere NEMA Contac- tor is the smallest which exceeds the calculated rated current minimum of 34.6 amperes. Since all of the IT . Con- tactors are rated for up to 600 volt operation (U e ), the calculated rated voltage limit is also met. Altitude (AL T) Voltage Factor (VF) Current Factor (CF) 6,562 feet (2000 m) 8,202 feet (2500 m) 9,843 feet (3000 m) 1 0.93 0.87 1 0.97 0.95 13,123 feet (4000 m) 16,404 feet (5000 m) 0.77 0.67 0.90 0.85

IT Altitude Considerations (Derating) - Application Note

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