Safety Switch Ratings - EandM
Safety Switch RatingsAmpere RatingSiemens safety switches are available in two types: generalduty and heavy duty, both of which are listed by UnderwritersLaboratories (UL). Every safety switch has a specific ampererating, which is the maximum continuous current it can carrywithout causing deterioration or exceeding temperaturerise limits. General duty switches are available with ampereratings of 30, 60, 100, 200, 400, and 600 amperes. Heavy dutyswitches are rated for 30, 60, 100, 200, 400, 600, 800, and 1200amperes. (Though not discussed in this course, bolted pressureswitches are also available, with ampere ratings of 800, 1200,1600, 2000, 2500, 3000, and 4000 0060SG eneralDuty30GeneralDuty38HeavyDutyBoltedPressure
Short CircuitWithstandabilitySafety switches must be capable of withstanding thelargest potential short circuit current that can occur in theselected application. General duty switches have a maximumshort circuit withstandability of 100,000 amperes, while theequivalent rating of heavy duty switches is 200,000 amperes.Voltage RatingSafety switches are also rated according to the maximumvoltage they can handle. The voltage rating of the switch mustbe at least equal to the circuit voltage. In other words, it can behigher than the circuit voltage, but never lower. For example,a safety switch rated for 600 volts can be used on a 480 voltcircuit, but a switch rated for 240 volts must not be used ona 480 volt circuit. The following chart reflects available voltageratings.SG eneral DutyGeneral DutyHeavy DutyBolted Pressure240 VAC250 VDC240 VAC600 VAC600 VDC240 VAC480 VAC600 VAC**600 VAC Bolted PressureSwitch in not UL Listed39
Dual Horsepower RatingsAll Siemens safety switches have two horsepower ratings formotor applications. This is referred to as “dual horsepowerrated.” For example, a switch might have a standard rating of 10HP, and a maximum rating of 30 HP. The standard rating, 10 HP,applies when non-time delay fuses are used.Non-Time Delay FuseUse Standard HP RatingFusibleEnclosedSwitchThe maximum rating of 30 HP applies when time delay fusesare used.Time Delay FuseUse Maximum HP RatingFusibleEnclosedSwitchThe following chart reflects the range of horsepower ratings forSiemens safety switches.Safety Switch TypeGeneral DutyHeavy Duty40VoltageHorsepower Range240 VAC1½ - 200250 VDC5-50240 VAC1½ - 250600 VAC3-500250 VDC5-50600 VDC15-50
Switch Circuit Types And TerminologyPoleThe term pole refers to the number of wires that a switchwill disconnect at one time. The following drawing, forexample, shows a 3-pole safety switch. The three circuits aremechanically connected so that all three poles connect anddisconnect the line and load simultaneously when the switchis operated. In this case, each pole is fused for overcurrentprotection.Fuse3-Pole, 3-Fuse41
Circuit ConfigurationsFollowing are circuit configuration diagrams for 2- and 3-polesafety switches. Safety switches may be fusible, non-fusible, orfusible with a solid , 2-Wire2-Pole, 3-WireSolidNeutral3-Pole3-Pole, 3-Wire3-Pole, 4-WireThe following circuit configurations are available in Siemenssafety switches:2-Pole3-Pole6-Pole (not shown)2-Pole, 2-Wire3-Pole, 3-Wire4-Pole, 4-Wire (not shown)6-Pole, 6-Wire (not shown)2-Pole, 3-Wire3-Pole, 4-Wire42
ExampleThe circuit configuration required depends on the load and onthe power supply connected to it. For example, a three-phasemotor needs a 3-pole switch to connect it to a three-phasepower supply. If overcurrent protection is required, a fusible3-pole safety switch should be selected, as in the followingexample.3Ø AC Power Supply3ØMotor43
Switch ThrowsAll the example switches shown so far have been single throw.“Throw” is the term used to refer to the number of differentpositions a switch has, that is, the number of different circuitsit can connect a given wire to. Switches may be single throw,double throw, or multiple throw. The simplest is a single pole,single throw:Next in complexity is the single pole, double throw which canconnect a single wire to one of two different circuits:Two- and three-pole single throw switches have already beenshown. The double pole, double throw (DPDT) switch canconnect each of two different wires to two different circuits:Many different arrangements are possible. The followingillustrates only a few of them:DPDT44DP3T3P3T
Catalog NumbersTo help identify each type of safety switch, a catalog numberis assigned. The catalog number provides a description of thesafety switch. There are eight parts to the catalog number ofSiemens VBII Safety Switches. The following figure illustrates atypical catalog number.Catalog Number Part 1 Part 2 Part 3 Part 4 Part 5 Part 6 Part 7 Part 8HF364NRCU Part 1HF364NRCUPart 1 indicates the switch type. There are three typesavailable: General Duty 10k AIC Max. (Plug Fused & 60A MaxNon-Fused); General Duty; and Heavy Duty.DesignatorSwitch TypeLGeneral Duty 10k AIC MaxGGeneral DutyHHeavy DutyDTHeavy Duty Double ThrowDTGGeneral Duty Double ThrowFrom the above table, one can see that the example switch,type H, is a heavy duty switch.Part 2Part 2 indicates whether the switch is fused or non-fused. “F”designates a fused switch; while “NF” designates non-fusedtypes. The example switch is fused.45
Part 3Part 3 of the catalog number indicates the number of poles.Siemens VBII safety switches can be provided with 1, 2, or 3poles. (A neutral, if required, is not included in the number ofpoles.) The following shows a 3-pole safety switch used witha 3-phase AC motor. The example catalog number calls for a 3pole safety switch.Three-PhaseSupply Power3-Pole Enclosed SwitchMotorPart 4Part 5Part 4 of the catalog number indicates the voltage rating.The example catalog number indicates a safety switch with amaximum voltage rating of 600 volts.DesignatorVoltage1120V or 120/240V2240V6600VPart 5 of the catalog number refers to the switch’s currentrating. The example indicates a safety switch with a 200ampere rating.Designator Amperes46130A260A3100A4200A5400A6600A7800A81200A
Part 6Part 6 of the catalog number indicates whether or not a neutralis included with the switch. If no neutral is needed, part 6 of thecatalog number is simply omitted. If a neutral is needed, an “N”is added to the catalog number, as in the example.Part 7Part 7 of the catalog number indicates the type of enclosure.The example catalog number indicates a safety switch in aNEMA Type 3R outdoor enclosure.Part 8DesignatorEnclosure TypeOmitType1, IndoorRType 3R, OutdoorSType 4/4X, Stainless SteelXType 4/4X, Non-MetallicJType 12, IndustrialPart 8 of the catalog number is for special applications. Thefollowing table lists the possible applications. For example,“CU” indicates factory-installed copper wire grips, as in therepresentative catalog number given above.DesignatorSpecial Applications With:CHCrouse-Hinds ReceptacleCJFactory J Fuse SpacingsCRClass R Clips InstalledCUCopper Wire Grips InstalledGFactory-Installed Ground BarPNPyle-National ReceptacleWViewing Window47
Review 41.The rating is the maximum continuouscurrent a safety switch can carry.2.The maximum short circuit current withstandability ofheavy duty switches is amperes.3.The maximum horsepower available in a 240 VAC general duty safety switch is HP.4.A describes the number of isolatedcircuits that can pass through the safety switch at onetime.5.The number “3” in part five of the heavy duty catalognumber indicates .a.c.3-pole100 amperesb.d.3R enclosure600 VAC6. refers to the number of different positionsof a given switch.48
General Duty Safety SwitchesGeneral duty switches are intended for use primarily on powersupplies rated at 240 VAC or less, where the available faultcurrent is less than 100,000 amperes (with Class R or T fuses,or 10,000 A max with Class H fuses). They can be supplied in aType 1(indoor) or Type 3R (outdoor) enclosure.Plug Fuse TypeSafety SwitchThe general duty plug fuse type switch is available for 120or 240 volt systems. It is suitable for one- or two-poleapplications, and is rated at 30 amperes. A separately supplied,30-ampere Type S plug fuse is required. This switch is availablefor use on two-wire or three-wire motor applications up tothree horsepower. A non-fusible model comes in a two-poleconfiguration. It is rated at 60 amperes, and can be used withmotors up to 10 HP. There are also pullout models available infused and non-fused versions.General Duty SwitchesThe fusible general-duty safety switch is available in twoand three poles, both with solid neutral, or with four poles.The non-fusible model is available with a two- or three-poleconfiguration. Fusible switches accept Class H fuses asstandard. A field-installable rejection kit is available whichrejects all but Class R fuses. All general duty switches haveboth cover and handle padlocking capabilities.RatingsAmpere ratings: 30, 60, 100, 200, 400, or 600 amperesFuses: 1 - 600 ampere Class H, K, or R70 - 600 ampere Class T cartridge fuseVoltage ratings: 240 VAC, 250 VDCMax short-circuit current withstandability: 100,000amperes (with current limiting fuses)49
Type 1 EnclosureGeneral duty switches are available in the NEMA Type 1enclosure, which is intended for indoor use. An interlockprevents the cover from being opened when the switch is inthe “On” position. A cover interlock also prevents turning theswitch “On” with the door open. (There is a front operablerelease for this feature.) This enclosure is intended primarily toprovide protection against contact with the safety switch, and isused in locations where unusual service conditions do not exist.SG en eral D utyGeneral DutySafety SwitchType 1 Enclosure50
Type 3R EnclosureGeneral duty 2- and 3-pole safety switches are also suppliedin a Type 3R enclosure, which is intended for outdoor use, andprovides a degree of protection against falling rain and sleet. Itis also able to withstand the formation of ice on the enclosurewithout damage, but is not intended to provide protectionagainst conditions such as dust, internal condensation, orinternal icing.SG en eral D utyGeneral DutySafety SwitchType 3R Enclosure51
Heavy Duty Safety SwitchesType 1 EnclosureHeavy duty safety switches can be used on power suppliesup to 600 Volts, AC or DC. They can be used in applicationswhere the available fault current is 200,000 amperes or less. Acover interlock prevents inadvertant opening of the cover whilethe switch is in the “On” position, and a mechanism interlockprevents inadvertant turning on of the switch while the cover isopen. Heavy duty safety switches also have cover and handlepadlocking capabilities.Type 1 Enclosure52
Enclosures for HeavyDuty Safety SwitchesHeavy duty safety switches can also be supplied withType 3R, 4 / 4X, and 12 enclosures.Type 12Type 4X StainlessType 3RRatingsCurrent ratings: 30, 60,100,200, 400, 600, 800, & 1200amperesFuses: 1 - 600 ampere Class H, J, K, and R cartridge fuses1 - 1200 ampere Class T cartridge fuses601-1200 ampere Class L bolt-in fuses(Fusible 800 and 1200 A switches have Class L fuseprovisions as standard)Voltage ratings: 240 /480/ 600 VAC; 250 / 600 VDCMax short-circuit current withstandability: 200,000 amperes53
Interlock ReceptacleThe interlock receptacle safety switch provides cord connectionfor heavy-duty portable equipment such as refrigerated trucks,welders, and other portable electric tools. It is fitted with aCrouse-Hinds Arktite or similar receptacle.This receptacle isinterlocked to prevent insertion or removal of the plug if theswitch is in the “On” position. The Crouse-Hinds receptacleswitch requires a Crouse-Hinds 4-wire, 3-pole, style 2,grounded APJ plug. The interlock receptacle safety switchesare rated for 30, 60, and 100 amperes. The enclosure meets therequirements for Type 4, 4X, or 12/3R enclosures.ReceptacleArktite is a registered trademark of the Crouse-Hinds Company.54
Four- and Six-PoleSafety SwitchesFour- and six-pole heavy-duty safety switches are availablein current ratings of 30 - 200 amperes, in Type 1 / 3R / 12 orType 4 / 4X enclosures, fusible or non-fusible. These switchesare commonly used as a disconnecting means for two-speed,two-winding motors. A 4-pole switch is also used in 3-phase,4-wire circuits when a switching neutral is required.Double Throw SwitchesDouble throw switches are used to transfer loads from onepower source to another. For example, a critical piece ofequipment often needs a back-up power supply in case themain power supply fails or needs maintenance. Double throwswitches are also used to connect a single power source toeither of two loads. 30-600A double-throw fusible switchesare available in Types 1 and 3R enclosures, while non-fusiblemodels are available in Types 1 and 3R for 30 to 1200A, and in4 / 4X and 12 for 30 to 200A. Double throw switches are ratedfor 240 VAC/250 VDC or 600 VAC.55
Double ThrowSwitch ApplicationA motor, for example, can be connected through a doublethrow switch to power supply A or power supply B. When thehandle is in the center position the switch is “Off” and no powerflows to the motor.From Power Supply AHandleCenterMotorFrom Power Supply BMoving the handle to the up position connects the motor topower supply A.From Power Supply AHandleUpMotorFrom Power Supply BMoving the handle to the down position connects the motor topower supply B.From Power Supply AHandleDownMotorFrom Power Supply B56
Safety Switch AccessoriesA full range of accessories is available for Siemens VBII SafetySwitches. Some of these are shown below.Both General Duty and Heavy Duty Switches are fieldconvertible to accept Class J or Class T fuses.HT63Class T Fuse Adapter KitStandard Neutral Kits can be field installed in both General andHeavy Duty Safety Switches, and UL listed 200% Neutrals areavailable on 100-600A Heavy Duty Switches.HN612Neutral KitHN264200% Neutral KitThe Multiple Padlock Accessory is a tamper-proof deviceto provide for multiple padlocking to meet OSHA or plantrequirements.SL0420Multiple Padlock Accessory57
The following illustrates some of the other accessories availablefor General and Heavy Duty Safety Switches.Copper Lug KitsAuxiliary ContactsHLC612HA161234Isolated Ground KitsFuse Puller KitsHG261234HP61Standard Ground KitsHG61234Class R Fuse Clip KitsHR612Heavy Duty Switches are UL approved to accept field installedCopper Lug Kits. Equipment Ground Kits are available for allGeneral Duty and Heavy Duty Switches. They come standardin Type 4 / 4X and Type 12 Switches, and are field installablein Type 1 and Type 3R. Isolated Ground Kits are also availablefor 30-600A Heavy Duty Switches. Some circuits with a highdegree of computer or other electronic loading require anisolated ground to prevent interference from the buildingground and neutral lines.58
Auxiliary Contacts are available only for Heavy Duty Switches.They come with 1 normally open and 1 normally closed or 2normally open and 2 normally closed contacts. A PLC AuxiliarySwitch for 30-200A switches is also available. It has very lowcontact resistance, which is compatible with the low voltagesand currents typically found in PLC circuits.HA261234Auxiliary Contract KitFuse Puller Kits are field installable in 30-100A Heavy DutySwitches.HP61Fuse Puller KitClass R Fuse Clips are used to prevent the installation ofnoncurrent-limiting Class H or Class K fuses. All General and30-600A Heavy Duty Switches are field convertible to acceptClass R Fuse Clip Kits.HR612Class R Fuse Clips59
Review 5601.The maximum short circuit current withstandability ofgeneral duty switches is amperes.2.The maximum short circuit current withstandability ofheavy duty switches is amperes.3.The maximum current rating of a VBII heavy duty switchthat is not a bolted pressure switch isamperes.4.The safety switch providescord connection for heavy duty portable equipment.5.switches are intended totransfer loads from one power source to another.
Selecting Safety SwitchesWhile selecting a safety switch is not difficult, flow charts canhelp to make it even easier. The following flow chart can beused to make key decisions in the selection of a safety switch.StartIs SelectNon-FusibleSwitchNoData Needed:1) System Voltage2) Full-Load Amps OfUtilization Device3) Number Of Poles(Solid Neutral?)4) EnvironmentIs It AMotorCircuit?YesData Needed:1) System Voltage2) Motor Horsepower3) Number Of Poles(Solid Neutral?)4) EnvironmentNoFuse Data Needed:1) Available FaultCurrent2) System Voltage3) Full-Load Amps OfUtilization Device4) Fuse Class5) Number Of FusesSwitch Data Needed:1) Available FaultCurrent2) System Voltage3) Full-Load Amps OfUtilization Device4) Number Of Poles(Solid Neutral?)5) Fuse Class6) EnvironmentIs It AMotorCircuit?YesFuse Data Needed:1) Available FaultCurrent2) System Voltage3) Full-Load Amps OfMotor4) Fuse Class5) Number Of FusesSwitch Data Needed:1) Available FaultCurrent2) System Voltage3) Motor Horsepower4) Number Of Poles(Solid Neutral?)5) Fuse Class6) Environment61
Selecting aNon-Fusible SwitchThe first question is: Is circuit protection required? If circuitprotection is not required a non-fusible switch would beselected.StartNoIs on-Fusible Switch notUsed on a Motor CircuitYesSelectFusibleSwitchIf a non-fusible switch is selected, the next question is: Is it amotor circuit? If the switch is not used on a motor circuit thefollowing information must be known:1) System voltage:120 VAC, 240 VAC, 480 VAC, 600 VAC,250 VDC, 600 VDC2) Full-load amperes of the device to be used on the switch3) The number of poles required, and if a neutral is needed4) The environment (enclosure type)SelectNon-FusibleSwitchNoData Needed:1) System Voltage2) Full-Load Amps OfUtilization Device3) Number Of Poles(Solid Neutral?)4) Environment62Is It AMotorCircuit?
Non-Fusible Switch Usedon a Motor CircuitIf the switch is used on a motor circuit, the same data is arequired, except that motor horsepower replaces full-loadcurrent.1) System voltage2) Motor horsepower3) The number of poles required, and if a neutral is needed4) The environment (enclosure type)SelectNon-FusibleSwitchNoIs It AMotorCircuit?Data Needed:1) System Voltage2) Full-Load Amps OfUtilization Device3) Number Of Poles(Solid Neutral?)4) EnvironmentSelecting a Fusible SwitchYesData Needed:1) System Voltage2) Motor Horsepower3) Number Of Poles(Solid Neutral?)4) EnvironmentIf circuit protection is required, a fusible switch would beselected.StartNoSelectNon-FusibleSwitchIs CircuitProtectionRequired?YesSelectFusibleSwitch63
Fusible Switch not Usedon a Motor CircuitIf a fusible switch is selected, the next question is: Is it amotor circuit? If not, the following information must be knownto select a fuse:1) Available fault current2) System voltage3) Full-load amperes of the device to be used on the switch4) Fuse class5) Number of lines to be fusedThe following must be known to select a switch:1) Available fault current2) System voltage3) Full-load amperes of the device to be used on the switch4) Number of poles, and if a neutral is needed5) Fuse class6) Environment (enclosure type)SelectFusibleSwitchNoFuse Data Needed:1) Available FaultCurrent2) System Voltage3) Full-Load Amps OfUtilization Device4) Fuse Class5) Number Of FusesSwitch Data Needed:1) Available FaultCurrent2) System Voltage3) Full-Load Amps OfUtilization Device4) Number Of Poles(Solid Neutral?)5) Fuse Class6) Environment64Is It AMotorCircuit?
Fusible Switch Used on aMotor CircuitIf the switch is used on a motor circuit, the followinginformation must be known to select a fuse:1) Available fault current2) System voltage3) Full-load amperes required by the motor4) Fuse class5) Number of lines to be fusedThe following must be known to select a switch:1) Available fault current2) System voltage3) Motor horsepower4) Number of poles, and if a neutral is needed5) Fuse class6) Environment (enclosure type)SelectFusibleSwitchNoFuse Data Needed:1) Available FaultCurrent2) System Voltage3) Full-Load Amps OfUtilization Device4) Fuse Class5) Number Of FusesSwitch Data Needed:1) Available FaultCurrent2) System Voltage3) Full-Load Amps OfUtilization Device4) Number Of Poles(Solid Neutral?)5) Fuse Class6) EnvironmentIs It AMotorCircuit?YesFuse Data Needed:1) Available FaultCurrent2) System Voltage3) Full-Load Amps OfMotor4) Fuse Class5) Number Of FusesSwitch Data Needed:1) Available FaultCurrent2) System Voltage3) Motor Horsepower4) Number Of Poles(Solid Neutral?)5) Fuse Class6) Environment65
Example of Selecting aNon-Fusible SafetySwitchIn the following example, a safety switch needs to beprovided for an application that does not require circuitprotection. The full-load current of the utilization device is 45amperes. It is not a motor. The system voltage is 240 VAC, 3phase, 3-wire (without neutral). The environment is indoors, andthere are no unusual conditions such as dust or liquids.Recall from earlier discussion that in general, all conductors(including the switch) must be capable of carrying 125% of thefull-load current. The full-load current of the utilization deviceis 45 amperes; a switch must be selected that can carry 56amperes.45 amperesX 125%56 amperesKnowing that the switch will be used indoors, with no unusualconditions, a Type 1 enclosure can be selected. The otherrequirements can be met with a general duty switch. Referringto the General Duty Safety Switches section of the Speedfaxcatalog, the first 240 volt, 3-pole, non-fusible switch that willhandle 56 amperes is a 60 amp switch. The catalog number isGNF322.Since the required fuse is a Class R, and the circuit has apotential fault current of 200,000 amperes, a class R fuse kit(catalog number HR64) is required. This can be found in theaccessory section of the Speedfax.Indoor - Type 1SystemAmpere Catalog ListShip Wt. CatalogRating Number Price Std. Pkg. Number240 Volt Non-Fusible2-Pole or 00GNF326Example of Selecting a66Outdoor - Type 3RList Ship Wt.Price Std. Pkg.GNF321RGNF322RGNF323RGNF324RUse 600V Switch - HF365RUse 600V Switch - HF366RIn the following example a safety switch needs to be
Fusible Safety Switchprovided for an application that does require circuit protection.This application will have a 480 VAC, three-phase, 75 HP motor,not needing a neutral connection. The customer has specifiedan RK5 time-delay fuse, for a potential fault current of 200,000amperes. The switch will be located indoors with no unusualservice conditions.The 480 VAC requirement dictates a heavy duty, 600 volt,fusible switch. Turning to the appropriate Speedfax page,the enclosure type is located, that is, Indoor — Type 1. Next,the 600 Volt Fusible, 3-pole, 3-fuse table is found. From thehorsepower ratings, in the 480 VAC, 3-phase, 3-wire section, aswitch will be selected from the maximum (Max.) column. Themaximum column is chosen because the customer selectedtime delay fuses. (Had non-time delay fuses been specified,the standard horsepower column would be used.) Readingdown the maximum horsepower column, 125 HP, the firstrating meeting the 75 HP requirement, is found. Reading to theleft the catalog number, HF364, is found under Type 1. (It canalso be seen that this safety switch is rated for 200 amperes.)Since the required fuse is a Class R, and the circuit has apotential fault current of 200,000 amperes, a Class R fuse clipkit (catalog number HR64) is also required. This can be found inthe accessory section of the Speedfax.Horsepower Ratings480 VAC1 Phase,3 Phase,Ship Wt. 2 WireAmpere Catalog List3 WireSystem Rating Number Price Std. Pkg. Std. Max. Std. Max.Indoor - Type 1600 Volt Fusible3-Pole, 20015306012525040050050067
Selecting a FuseSection 430.6 of the NEC requires that where the currentrating of a motor is used to determine the ampacity ofconductors or ampere ratings of switches, branch-circuitovercurrent devices, etc., the values given in Tables 430.247through 430.250 are required to be used instead of the actualmotor nameplate current rating. In order for a customer toproperly select a fuse, NEC Table 430.250 must be referredto. According to NEC Table 430.250, a 75 HP, 460 VAC motorhas a full-load current of 96 amperes.Table 430.250 Full-Load Current,Three-Phase Alternating-Current MotorsThe following values of full-load currents are typical for motor running atspeeds usual for belted motors and motors with normal torquecharacteristics.Motors built for low speeds (1200 rpm or less) or high torques mayrequire more running current, and multispeed motors will have full-loadcurrent varying with speed. In these cases, the nameplate current ratingshall be used.The voltages listed are rated motor voltages. The currents listed shallbe permitted for system voltage ranges of 110 to 120, 220 to 240, 440 to480, and 550 to 600 volts.Induction-Type Squirrel Cage and Wound Rotor 02631374960728395103118Reprinted with permission from NFPA 70-2005, the National Electrical Code , Copyright 2004,National Fire Protection Association, Quincy, MA 02269.
Table 430.52 of the NEC is provided to help select a fuse thatwill not trip while starting a motor, and still provide adequateovercurrent protection. According to this table, the NEC requires that the ampere rating of an AC motor protected by atime-delay fuse be multiplied by 175%.Table 430.52 Maximum Rating or Setting of Motor BranchCircuit Short-Circuit and Ground-Fault Protective DevicesPercentage of Full-Load CurrentType meBreaker300175800250800250AC polyphase motors other than wound-rotorSquirrel cage300175- otherthan DesignE or DesignB energyefficientDesign E orDesign 50Wound rotor150150800150Direct current(constantvoltage)150150250150Multiplying the motor rating of 96 amperes times 175% resultsin a fuse size of 168 amperes. Since this is a non-standard fusesize, the next standard fuse size of 175 amperes would beselected.96 amperesX 175%168 amperesFull-Load Motor CurrentNEC RequirementFuse Rating69
Review 6701.A safety switch would be selected whencircuit protection is not required.2.A safety switch would be selected whencircuit protection is required.3.When selecting a non-fusible safety switch for utilization device rated at 100 amperes, a switch must beselected that can carry amperes.4.According to the NEC , the ampere rating of an ACmotor protected by a time-delay fuse should be multiplied by %.
Review AnswersReview 11) fusible; 2) 50; 3) a; 4) overload, short circuit; 5) short circuit;6) overload; 7) peak let-thru; 8) energy; 9) 240; 10) 310.16;11) 125.Review 21) inverse; 2) half; 3) short; 4) Time-delay; 5) ampere;6) higher, lower; 7) 200,000.Review 31) 1; 2) 3R; 3) contacts; 4) two.Review 41) ampere; 2) 200,000; 3) 200; 4) pole; 5) c; 6) Throw .Review 51) 100,000; 2) 200,000; 3) 1200; 4) interlock receptacle; 5)Double throw.Review 61) non-fusible; 2) fusible; 3) 125; 4) 175.71
Final ExamThe final exam is intended to be a learning tool. The book maybe used during the exam. A tear-out answer sheet is provided.Please fill out the answer sheet neatly and completely. Aftercompleting the test, mail the answer sheet in for grading. Agrade of 70% or better is passing. Upon successful completionof the test a certificate will be issued.1.2.The following symbol represents a non-fusible enclosedswitch:a.c.b.d.A safety switch combined with fuses in a single enclosureis referred to as a safety switch.a.b.3.heavy dutygeneral duty1050c.d.25100With an increase of current, temperature will.a.b.72c.d.The National Electrical Code defines “in sight” as visibleand not more than feet distant.a.b.4.non-fusiblefusibleincreaseremain the samec.d.decreaseincrease and decrease
5.Overcurrent protection is covered by NEC article.a.b.6.AWGpeak currentc.d.instantaneous currentampacity rating26c.d.310Fuses have a/an time-current characteristic.a.b.9.780240According to the NEC a continuous load is a load wherethe maximum current is expected to continue forhours or more.a.b.8.c.d.The amount of current a conductor can carry on acontinuous basis is known as Class R fuses have an interrupting rating (AIC) ofamperes.a.b.10,00050,000c.d.100,000200,00010. A UL Type enclosure is intended for indooruse primarily to provide protection against contact with theenclosed equipment in locations where unusual serviceconditions do not exist.a.b.13Rc.d.41273
11.UL Type enclosures are intended for outdooruse primarily to provide a degree of protection againstfalling rain and sleet and must remain undamaged by theformation of ice on the enclosure. They are not intended toprovide protection against conditions such as dust, internalcondensation, or internal icing.a.b.13Rc.d.41212. The maximum ampere rating of a general duty switch
Switch Throws All the example switches shown so far have been single throw. “Throw” is the term used to refer to the number of different positions a switch has, that is, the number of different circuits it can connect a given wire to. Switches may be single throw, double throw, or multiple throw. The
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Thermal magnetic switch DIP (Dual In-line Package) Encapsulated switches Switch with delayed opening Double switch bipolar Time switch Timer Electronic limiter Mercury switch Inclination or motion detector Closed switch Switch delay when opening and closing Double limit switch
134-1400 LS EP Switch 265-1002 134-1402 LS EP Switch 265-1006 Original Part No. Mfg. Description Part No. 134-1403 LS EP Switch 265-1005 134-1404 LS EP Switch 265-1002 134-1405 LS EP Switch 265-1004 134-1406 LS EP Switch 265-1003 134-1407 LS EP Switch 265-1006 134-1452 LS Pressure Elec. Switch 134-1451 134-1456 LS Pressure Elec. Switch 134-1451 .
8.1-3 fsar cross-reference of discussion of srp acceptance criteria for electric power 8.2-1 power transformer ratings 8.2-2 isolated phase bus ratings 8.2-3 main generator ratings 8.2-4 switchgear ratings 8.2-5 ratings of low
Wiring accessories are used for connecting appliances (Fig. 3.4). (a) Switch A switch is used to make or break an electrical circuit. It is used to switch ‘on’ or ‘off ’ the supply of electricity to an appliance. There are various switches such as y surface switch y flush switch y ceiling switch y pull switch y push button switch y bed .
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