power distribution - Siemens

6MOLDED CASECIRCUIT BREAKERSMolded Case Circuit BreakersUnusual Operating ConditionsReferenceNote: The information provided on this and the next page is intended for reference and recommendation only. Because severalvariables can act on a circuit breaker’s performance at the same time, the data below is based less on controlled testing,than on experience and engineering judgment. Contact Siemens for further information on special conditions and treatment.High Ambient TemperaturesBecause thermal-magnetic trip breakersare temperature sensitive and calibratedfor a specific ambient of 40° C (104° F)(average enclosure temperature), ahigher ambient will cause the breaker totrip at lower current than its nameplaterating, in other words, causing thebreaker to “derate” (see Table 1).Similarly, the current carrying capacityof a circuit conductor is based upon acertain ambient temperature, a higherambient will reduce its current carryingcapacity, causing it to “derate.” Thus,with a fluctuating temperature, athermal-magnetic breaker will deratenearly parallel with its connected circuitconductors and maintain close circuitprotection. If the application temperatureexceeds 40° C (104° F) and is known,either a breaker specially calibrated forthe higher ambient or one oversizedaccording to Table 1 may be selected.In a case such as this, the circuitconductors should be oversized as well.Siemens Electronic Trip Unit Breakersare insensitive to temperature changes.However, they do include circuitry toprotect the components fromabnormally high temperatures.Moisture — CorrosionFor atmospheres having high moisturecontent and / or where fungus growth isprevalent, a special preventive treatmentmay be required.Where the air is heavily laden withcorrosive elements, breakers madewith special corrosion-resistantfinishes may be required.AltitudeReduced air density at altitudes greaterthan 6600 ft. (2000 meters) affects theability of a molded case circuit breakerto transfer heat and interrupt faults.Therefore, circuit breakers applied atthese altitudes should have interrupting,insulation and continuous currentsderated as indicated in Figure 1.Table 1 — Temperature Derating Data for Thermal-Magnetic BreakersReferenceAmpere Ampere Rating at:Rating at 25° C 50° C 60° C40° C (104° F) (77° F) (122° F) (140° F) Siemens Breaker Frames0015 0017 0013 00110020 0022 0018 00160025 0028 0023 0021BQ,0030 0033 0028 0026 BL,0035 0039 0030 0025 BQD,0040 0044 0037 00340050 0055 0046 0042CQD,0060 0066 0056 0052 NGG,0070 0077 0065 0060 NGB,0090 0099 0084 0078DGED0100 0110 0094 00870125 0137 0114 01000150 0165 0136 01200175 0192 0159 0140FG0200 0220 0182 01600225 0247 0205 01800250 0275 0235 02200300 0330 0276 02520350 0385 0325 0301JG0400 0440 0372 03400500 0550 0468 0435LG0600 0660 0564 05250700 0770 0658 0613MG0800 0880 0754 07040900 0990 0828 07491000 1100 0900 0825NG1200 1320 1090 10001400 1540 1304 11481600 1760 1500 13201800 1980 1690 14852000 2200 1880 1650Altitude in Feet (Meters)13,000 (4,000)12,000 (3,675)11,000 (3,350)10,000 (3,000)9,000 (2,750)8,000 (2,400)7,000 (2,100)PG6,000 (1,800)1.0 .95 .90 .85 .80 .75Rating Correction FactorFigure 1 — Altitude Adjustment6-144Siemens Power Distribution & Control, SPEEDFAX 2007-2008 Product Catalog