power distribution - Siemens

Molded Case Circuit BreakersDigital Solid State Sentron Sensitrip III SeriesTechnical6MOLDED CASECIRCUIT BREAKERSAdjustable “Ground Fault Pick-Up”SwitchSensitrip III circuit breakerscontaining the optional equipmentground fault protection cover theground fault pick-up range of 20% to70% of the circuit breaker framerating. The ground fault pick-upsettings also allow for one of threetime delays based on 12t curves.For 3-phase, 4-wire systems, anexternal neutral transformer isrequired with an ampere ratingequal to the trip unit ampere rating.l n = Maximum circuit breaker ampere rating.l r = Current Rating — a function of adjustment setting expressed in % of l n .l g = Ground Fault Pick-up — a function of adjustment setting expressed in % of l n .Examples of Adjustment SettingsCatalog Number SMD69800AA. Adjustable “ContinuousAmps” Rating SwitchAll Sensitrip III solid statemolded case circuit breakershave an adjustableampere rating switch.Adjustments made to thisswitch change thecontinuous current rating ofthe breaker from 20% to100% of its maximum tripunit rating depending onthe circuit breaker frame.B. Adjustable “Long TimeDelay” SwitchAll Sensitrip III circuitbreakers have anadjustable long time delayswitch to allow forselection of long timedelays of fixed timeintervals at six times thesetting of the adjustable“continuous amps”rating switch.C. Adjustable “InstantaneousPick-Up” SwitchSensitrip III circuit breakerswith an adjustableinstantaneous trip switchallow selection of a trippingpoint from related to theadjusted circuit breakerRating (l r ).Continuous Long Time InstantaneousI n = 800 Current Setting Delay Setting SettingI n = 800 amperes 30 12 8Results 240 amperes 12 seconds trip 1920 amperesl r = 30% of 800 at 6 x 240 amps = 1440. 8 x l r = 8 x 240D. Adjustable “Short TimePick-Up” Switch (Optional)Sensitrip III circuit breakerswith an adjustable short timepick-up switch allow forselection of short timepick-up in a range from 1.5to 10 times the setting of themaximum current rating.E. Adjustable “Short TimeDelay” Switch (Optional)Sensitrip III circuit breakerswith an adjustable short timepick-up switch also contain aswitch for adjustment intime delay. The adjustableshort time delay switchallows for either of twomodes of short time delays.One range of settingsenables the breaker to be setfor fixed time delays and theother range of settingsenables the breaker to be setfor short time delays basedon l 2 t curves.Catalog Number SMD69800ANGTLong Short Time Short Time Ground Groundl r Time Pick-Up Instantaneous Pick-Up Short Time l 2 T Fault Faultl n Setting Delay Off Setting On Delay Set Pick-Up Delay800 amperes 070 20 — 10 l r 8 l r .5 .28 40 .2Results 560 20 sec. — 5600A 4480A .5 secs .28 sec @ 4480A 320A .2 secA B C D E F G H I JA l n = 800 amperes.B l r = 560 amperes (70% of 800).C Delay = 20 seconds at 3360 amps (6 x l r ).Breaker will trip in 20 seconds with 3360amperes.D Short Time Pick-Up Off — Instantaneous can be used.E Instantaneous set at 10 x l r = 10 x 560 = 5600amperes.F Short Time Pick-Up On — Set at 8 = 8 x 560 = 4480amperes.G Short Time Delay = .5 seconds. (Definite Time)Note: G & H are mutually exclusive.H l 2 t switch on .28 seconds @ 6 x 560 = 3360 amperes.(Inverse time)I Ground Fault Pick-Up set at 40 = 40% of l n = 320amperes. (Definite Time)J Ground Fault Delay set at .2 seconds. Breaker will trip in200 milliseconds with a 400 ampere ground fault.6-74Siemens Power Distribution & Control, SPEEDFAX 2007-2008 Product Catalog