Instructions For Digitrip Models 220, 520, 520, 520M, And .

I.L. 70C1037H02Page 61.4 WiringThe internal components of the breaker, and how they arewired out to the breaker secondary contacts, are shown inthe breaker master connection diagram provided asAppendix C.1.5 Plexiglass CoverA clear, tamper-proof, plexiglass door sits on the breakercover. This door allows the settings to be viewed but notchanged, except by authorized personnel. The plexiglasscover meets applicable tamper-proof requirements. Thecover is held in place by two cover screws. Security isinsured by the insertion of a standard meter seal throughthe holes in both of the cover retention screws. Theplexiglass cover has an access hole for the Step buttonon the 520M and 520Mi units.1.6 Ground Alarm/Power Supply Module (520M Models only)The Ground Alarm/Power Supply Module (see Figure 1.4)is an optional accessory for the Digitrip 520M and 520Mimodels. The module can be installed beneath the metalmounting plate of the trip unit in the Magnum CircuitBreaker. The module covers the following input voltageratings: 120 VAC (7802C83G01), 230 VAC(7802C83G02), and 24/48 VDC (7802C82G01).1.6.1 Auxiliary PowerWhen the module is wired as shown in Figure 1.5, it willprovide an auxiliary power supply so that the 520M/520Miliquid crystal display (LCD) will be functional even whenthe circuit breaker has no load. A Digitrip 520M unitwithout auxiliary power will not display data until loadcurrent reaches approximately 25% 1 phase or 10%3 phase of the (In) rating.Figure 1.4 Optional Ground Alarm/Power Supply Modulefor 520M Trip Unit1.6.2.2 Ground Fault Alarm1.6.2 Ground AlarmA second function of the module is to provide either aground trip or ground alarm only output contact via therelay supplied in the module. On Digitrip 520M modelswith ground fault protection, an LED on the front of theunit also provides an indication of ground fault trip.1.6.2.1 Ground Fault TripWhen the Ground Alarm/Power Supply module is usedwith the MLSIG model, this unit will provide ground faulttrip contacts when the circuit breaker trips on a groundfault. You must then push the Reset button on the Digitripin order to reset the contacts (see Figure 1.5, Note 3).A ground fault alarm alerts a user to a ground faultcondition without tripping the circuit breaker. A red AlarmOnly LED on the front of the trip unit will indicate thepresence of a ground fault condition that exceeds theprogrammed setting.The ground fault alarm relay is energized when theground current continuously exceeds the ground faultpickup setting for a time in excess of a 0.1 second delay.The alarm relay will reset automatically if the groundcurrent is less than the ground fault pickup (see Figure 1.5, Note 4).Effective 8/13/99Courtesy of NationalSwitchgear.com

I.L. 70C1037H02Page 7OLOverload (Digitrip in overload mode)Pushing the Step button while the unit is in the OLmode will have the unit again display the overloadcurrent value.HELPThis message can indicate more than one problem with the trip unit. If the rating plug is missing,a HELP message and an Instantaneous trip LEDlight will be observed. The rating plug needs to beinstalled and the Instantaneous trip LED must becleared by pressing the Reset/Battery Test button.This message could also indicate that the trip unitis out of calibration and should be replaced at theearliest opportunity.1.8 StandardsThe Digitrip 220, 520, and 520M Trip Units are listed bythe Underwriters Laboratories, Inc., under UL FileE52096, for use in Magnum Circuit Breakers. These sameunits are also listed by the Canadian Standards Association (CSA) under file LR 43556.Figure 1.5 Wiring Diagram for 520M Models and GroundAlarm/Power Supply ModuleAll Digitrip units have also passed the IEC 947-2 testprogram which includes radiated and conducted emissiontesting. As a result, all units carry the CE mark.2.0 GENERAL DESCRIPTION OF MAGNUM CIRCUIT BREAKERS1.7 Display Feature (520M family only)2.1 GeneralThe Digitrip 520M and 520Mi models have a user interface in addition to the green and red LED trip indicators.This seven element display performs a metering functionand can be used to monitor load currents.Magnum Circuit Breakers are tripped automatically onoverload fault current conditions by the combined action ofthree components:When the Step button on the face of the trip unit ispressed and released, the display will show PH 1, forPhase 1 or A, and the current value. If the Step button isnot pressed again, the display will continue to show thecurrent value for Phase 1. Each time that the Step buttonis pressed, the next monitored function will be displayed.The other readings can be displayed in the sequencebelow:PH 2Phase 2 (B)PH 3Phase 3 (C)PH 4NeutralPH 5Ground (if Ground function is supplied)HIHighest phase currentEffective 8/13/99Courtesy of NationalSwitchgear.com1. The Sensors, which measure the current level2. The Digitrip Trip Unit, which provides a tripping signalto the Trip Actuator when current and time delaysettings are exceeded3. The low-energy Trip Actuator, which actually trips thecircuit breakerFigure 2.1 shows this tripping circuit for a typical MagnumBreaker. This arrangement provides a very flexiblesystem, covering a wide range of tripping characteristicsdescribed by the time-current curves referenced in Section9.2.The automatic overload and short circuit tripping characteristics for a specific circuit breaker are determined bythe ratings of the installed current sensors with a matchingrating plug and the selected functional protection settings.Specific setting instructions are provided in Section 4.

I.L. 70C1037H02Page 8When the functional protection settings are exceeded, theDigitrip unit supplies a trip signal to the Trip Actuator. As aresult, all tripping operations initiated by the protectionfunctions of the Digitrip Trip Unit are performed by itsinternal circuitry. There is no mechanical or direct magnetic action between the primary current and the mechanical tripping parts of the breaker, and external controlpower is not required.WARNINGIMPROPER POLARITY CONNECTIONS ON THE TRIPACTUATOR COIL WILL DEFEAT THE OVERLOADAND SHORT CIRCUIT PROTECTION, WHICH COULDRESULT IN PERSONAL INJURY.OBSERVE POLARITY MARKINGS ON THE TRIPACTUATOR LEADS AND CONNECT THEM PROPERLY, USING THE INSTRUCTIONS PROVIDED.2.2 Low-Energy Trip Actuatorlocated under the black molded platform on which theDigitrip unit is supported. The Trip Actuator contains apermanent magnet assembly, moving and stationary coreassemblies, a spring, and a coil. Nominal coil resistanceis 25 ohms and the black lead is positive. The circuitbreaker mechanism assembly contains amechanism-actuated reset lever and a trip lever toactuate the tripping action of the circuit breaker.When the Trip Actuator is reset by the operating mechanism, the moving core assembly is held in readinessagainst the force of the compressed spring by the permanent magnet. When a tripping action is initiated, the lowenergy Trip Actuator coil receives a tripping pulse fromthe Digitrip unit. This pulse overcomes the holding effectof the permanent magnet, and the moving core is released to trigger the tripping operation via the trip lever.2.3 Ground Fault ProtectionNOTE: The Digitrip Model 220 is not available withground fault protection. Only the 520 family has groundfault types available.The mechanical force required to initiate the trippingaction of a Magnum Circuit Breaker is provided by aspecial low-energy Trip Actuator. The Trip Actuator isFigure 2.1 Tripping Circuit for a Typical Magnum Breaker (Partial)Effective 8/13/99Courtesy of NationalSwitchgear.com

I.L. 70C1037H02Page 92.3.1 GeneralWhen the Digitrip 520 family includes ground fault protection features, the distribution system characteristics (forexample, system grounding, number of sources, numberand location of ground points, and the like) must beconsidered along with the manner and location in whichthe circuit breaker is applied to the system. These elements are discussed in Sections 2.3.3 through 2.3.6.The Digitrip 520 family uses three modes of sensing todetect ground fault currents: residual, source ground, andzero sequence (see Table 2.1). Magnum Circuit Breakerscan accommodate all three types, except for 4-polebreakers. The breaker secondary contact inputs B-6, B-7are used to configure the breaker cell positions for thethree schemes. No jumper from B-6 to B-7 programs theunit for a residual ground fault scheme, while a jumperfrom B-6 to B-7 programs the trip unit for either a sourceground or zero sequence configuration. If present, thisjumper resides on the stationary side of the switchgearassembly. In all three schemes, the proper current sensorinput is required on the external sensor input terminalsB-4, B-5 of the breaker secondary contacts.Table 2.1 Digitrip Sensing ModesGround (Earth)FaultSensing MethodBreakerSecondaryContacts Req’dApplicableBreakersFigureReferenceResidualNo Jumper3 or 4 pole2.2, 2.3, 2.5, 2.9Digitrip GFSensingElementUsedelement R5Source GroundJumper B6 to B73 pole only2.7element R4Zero SequenceJumper B6 to B73 pole only2.8element R4Note: This information applies to Trip Units with Ground2.3.2 Residual SensingResidual Sensing is the standard mode of ground faultsensing in Magnum Circuit Breakers. This mode utilizesone current sensor on each phase conductor and one onthe neutral for a 4-wire system (shown in Figures 2.2and 2.3). If the system neutral is grounded, but no phaseto neutral loads are used, the Digitrip 520 family of unitsincludes all of the components necessary for ground faultprotection. This mode of sensing vectorially sums theoutputs of the three or four individual current sensors. Forseparately-mounted neutrals, as long as the vectorial sumis zero, then no ground fault exists. The neutral sensormust have characteristics and a ratio which are identicalto the three internally-mounted phase current sensors.Available types of neutral sensors are shown in Figure 2.4. Residual ground fault sensing features areadaptable to main and feeder breaker applications.Available ground fault pick-up settings employing Residual Sensing are given in Table 2.2. Figure 2.5 shows a4-pole breaker with Residual Ground Fault Sensing.Effective 8/13/99Courtesy of NationalSwitchgear.comCAUTIONIF THE SENSOR CONNECTIONS ARE INCORRECT, ANUISANCE TRIP MAY OCCUR. ALWAYS OBSERVETHE POLARITY MARKINGS ON THE INSTALLATIONDRAWINGS. TO INSURE CORRECT GROUND FAULTEQUIPMENT PERFORMANCE, CONDUCT FIELDTESTS TO COMPLY WITH NEC REQUIREMENTSUNDER ARTICLE 230-95(C).2.3.3 Source Ground SensingDepending upon the installation requirements, alternateground fault sensing schemes may be dictated (seeFigures 2.6 and 2.7). The ground return method is usuallyapplied when ground fault protection is desired only on themain circuit breaker in a simple radial system. Thismethod is also applicable to double-ended systems wherea mid-point grounding electrode is employed. For thismode of sensing, a single current sensor mounted on theequipment-bonding jumper directly measures the totalground current flowing in the grounding electrodeconductor and all other equipment-grounding conductors.The settings shown in Table 2.1 will apply when theneutral sensor is not the same as the frame rating in aground return sensing scheme.2.3.4 Zero Sequence SensingZero Sequence Sensing, also referred to as vectorialsummation (see Figure 2.8), is applicable to mains,feeders, and special schemes involving zone protection.Zero Sequence current transformers (4 ½" x 13 ½"[114 mm x 342 mm] rectangular inside dimensions) areavailable with 100:1 and 1000:1 ratios.2.3.5 Multiple Source/Multiple GroundA Multiple Source/Multiple Ground scheme is shown inFigure 2.9. In this figure, a ground fault is shown whichhas two possible return paths, via the neutral, back to itssource. The three neutral sensors are interconnected tosense and detect both ground fault and neutral currents.Call Cutler-Hammer for more details on this scheme.2.3.6 Ground Fault SettingsThe adjustment of the ground fault functional settings(FLAT response or I2t) is discussed in Section 4.8. Theeffect of these settings is illustrated in the ground faulttime-current curve referenced in Section 9. Applicableresidual ground fault pick-up settings and current valuesare given in Table 2.2 as well as in the ground time-currentcurve.

I.L. 70C1037H02Page 10Table 2.2 Ground (Earth) Fault Current Settingsrating specified on the plug label. The current sensorrating can be viewed through openings in the back of thebreaker.Ground Fault Current Settings(Amperes)1InstalledSensor/Rating Plug(Amperes) In.25.30.35200506025063752.5 Current Sensors (Magnum Frames greater than 12375438500625750938125016004004805606408009601200 1600220005006007008001000120015002 920224002 3200216002200022400230002 0023000237502 5000263003157518902205252031503780472563001. Tolerance on settings are 10% of values shown.2. On Models 520 LSIG and 520M LSIG, the shaded values are set to a maximumtrip value of 1200 amperes for NEC.The six (3-pole) or eight (4-pole) current sensors installedin the circuit breaker are located on the lower conductors.The poles are paralleled and the corresponding currentsensors are also paralleled (see Figure 2.3). For example, a 4000A breaker phase rating has two 2000:1current sensors wired in parallel, which provides anoverall ratio of 4000:2. The auxiliary current transformershave a ratio of 20:1 for this size breaker which furthersteps down the rated current to 100 milliamperes and isequivalent to 100% (In) to the Digitrip.3.0 PRINCIPLES OF OPERATION3.1 GeneralThe Digitrip DT20 family of trip units is designed forindustrial circuit breaker environments where the ambienttemperatures can range from –20 C to 85 C but rarelyexceed 70 to 75 C. If, however, temperatures in theneighborhood of the trip unit exceed this range, the tripunit performance may be degraded. In order to insure thatthe tripping function is not compromised due to an overtemperature condition, the Digitrip 520 family microcomputer chip has a built-in over-temperature protectionfeature, factory set to trip the breaker if the chip temperature is excessive. On the 520 family, if over-temperatureis the reason for the trip the red Long Delay Time LED willflash.3. See Section 2.5.2.4 Current Sensors (Magnum Frames less than or equal to3200A)The three (3-pole) or four (4-pole) primary current sensorsare installed internally in the circuit breaker on the lowerconductors of the breaker. The current sensor ratingdefines the breaker rating (In). For example, 2000A:1Asensors are used on a 2000A rated breaker. There arefour auxiliary current transformers with a ratio of 10:1which further step down the rated current to 100 milliamperes, which is equivalent to 100% (In) to the Digitrip.The primary current sensors produce an output proportional to the load current and furnish the Digitrip DT20family with the information and energy required to trip thecircuit breaker when functional protection settings areexceeded.If a set of current sensors with a different ratio are installed in the field, the rating plug must also be changed.The associated rating plug must match the current sensorThe Digitrip uses the Cutler-Hammer custom-designedSµRE chip , an integrated circuit that includes amicrocomputer to perform its numeric and logic functions.The principles of operation of the trip unit are shown inFigure 3.1.In the Digitrip DT20 family of trip units, all sensing andtripping power required to operate the protection functionis derived from the current sensors in the circuit breaker.The secondary currents from these sensors provide thecorrect input information for the protection functions, aswell as tripping power, whenever the circuit breaker iscarrying current. These current signals develop analogvoltages across the current viewing resistors. The resulting a

Magnum and Magnum DS Breakers. Throughout this Instructional Leaflet, the use of the term “Magnum Breakers” refers to both the Magnum and Magnum DS low-voltage, ac power circuit breakers. The Magnum Digitrip line of trip units consists of the 220, 520, and 520M for UL stan