API API-SIEE Source Inspector Electrical Equipment Exam Practice Test

The correct answer isA. Metallic shielding components in cables, such asshield tapes, drain wires, metallic braids, or similar conductive shielding layers, are connected to theequipment grounding system, commonly through anequipment grounding busbaror other approved grounding termination point. The purpose of this connection is to provide a low-impedance path for induced voltages, capacitive charging current, noise, and fault-related currents, while also helping reduce electromagnetic interference and maintaining personnel safety.

In source inspection and quality surveillance of electrical systems, correct shield termination is important because improper grounding can lead to noise problems, unreliable signal performance, unsafe touch potentials, or ineffective fault-current control. The inspector therefore checks that cable shields and associated metallic components are terminated in accordance with the approved drawings, cable schedules, and project grounding requirements.

The other options are incorrect. Aceramic insulatordoes not provide the required grounding path. Alow voltage connectoris too generic and is not the intended grounding termination. Atransformer center tapis a system neutral point, not the correct destination for cable metallic shielding. Therefore, the proper connection point is theequipment grounding busbar.

The correct answer isD. API RP 14FZ. This document is specifically intended for thedesign and installation of electrical systems on fixed and floating offshore petroleum facilitieswhere equipment may be located inunclassified areas and hazardous classified areas identified as Class I, Zone 0, Zone 1, and Zone 2. The key clue in the question is the use of theZoneclassification system. In API and offshore electrical practice,API RP 14FZaddresses the offshore application of the zone-based hazardous area approach.

By contrast,API RP 14Fis associated with offshore electrical system guidance using the olderdivision-basedclassification approach rather than the zone terminology.NFPA 70is the National Electrical Code and is broader in scope; it is not the specific offshore petroleum recommended practice asked here.IEEE 841relates to severe-duty squirrel-cage induction motors and does not cover complete offshore electrical system design and installation requirements.

For source inspectors, recognizing the correct governing document is important because inspection and surveillance activities must verify compliance against the applicable design basis, hazardous-area classification method, and purchaser specification.

The correct answer isA, basic impulse level. On medium voltage equipment, thebasic impulse level BILis the highest voltage-related rating normally associated with the insulation system. BIL represents the ability of the equipment insulation to withstand a specified high-voltage impulse, such as a lightning surge or switching surge, without failure. It is therefore a dielectric withstand rating that is higher than the equipment’s normal operating or system voltage and is used to define insulation coordination for the equipment.

The other choices are not the best answer.Nominal voltageidentifies the intended system operating voltage class, but it is not the highest voltage-related rating.AC high potentialandDC high potentialare test voltages used during dielectric testing, not the principal nameplate rating that defines the equipment’s insulation impulse withstand capability. In source inspection of switchgear and other medium voltage assemblies, the inspector verifies that the equipment ratings, including voltage class, insulation level, and test records, agree with the purchase specification and applicable standards.

Because BIL expresses the highest recognized insulation withstand rating among the listed options,Ais the verified answer.

The correct answer isB. Formedium-voltage motor terminal boxes, IEEE 841 requires an added safety provision because these enclosures contain higher-energy terminations and present a more serious shock and arc-flash hazard than standard low-voltage terminal boxes. Apermanent locking mechanismis therefore required for terminal boxes used on motors above1000 V, and also for certain large frame motors at1000 V, to prevent unauthorized or accidental access while the motor is energized. This requirement supports safe operation, maintenance control, and electrical isolation practices.

From an API source-inspection perspective, this falls under verification ofelectrical safety features, enclosure construction, and compliance with the applicable motor standardduring shop inspection and surveillance. The API guide includeselectric motors over 500 HPamong the covered equipment categories and emphasizes checking conformance to applicable codes, referenced standards, drawings, and purchase specifications during manufacture and inspection. A drain fitting may be required on some terminal boxes for moisture control, and grounding provisions are also important, but those are not the specific IEEE 841 requirement identified in this question. The distinctive requirement here is thepermanent locking mechanism.

The correct answer isD. Forexplosionproof threaded conduit joints,API RP 540requires a minimum offive fully engaged threads. This requirement is critical because explosionproof joints are intended tocontain an internal explosionand prevent flame propagation into the surrounding hazardous atmosphere. The threaded path acts as a controlled flame path, cooling and quenching hot gases before they can exit the enclosure or conduit system at an ignition-capable temperature.

If too few threads are engaged, the flame path may be inadequate, reducing the joint’s mechanical strength and compromising its ability to contain pressure and hot gases generated by an internal fault or ignition event. In hazardous locations, this becomes a major safety issue, especially for conduit-connected equipment such asjunction boxes, motors, control panels, and other Class I installations. During source inspection and quality surveillance, the inspector should verify not only that the correct explosionproof fittings are used, but also that the conduit joints are properly assembled with the required thread engagement and in accordance with the governing hazardous-area standard and approved drawings. Therefore, the minimum required number of fully engaged threads isfive, makingoption Dthe verified answer.

The correct answer isB. Forliquid-immersed transformers, the four-letter cooling code is used to describe both thecooling mediaand themethod of circulationfor the internal and external cooling systems. In this code structure, thefirst letteridentifies theinternal cooling mediumthat is in contact with the windings, while thesecond letteridentifieshow that internal cooling medium circulates. This may be by natural circulation or by forced circulation, depending on the transformer design. Thethird letterthen identifies theexternal cooling medium, and thefourth letterindicates thecirculation method of that external medium.

This coding is important in source inspection because the cooling class affects transformer rating, heat dissipation capability, accessories, and verification of nameplate data. During inspection and surveillance, the source inspector checks that the specified cooling class on the nameplate, drawings, and test documentation matches the purchase requirements and transformer design. Misidentifying the cooling code can lead to misunderstanding of the transformer’s thermal performance and service suitability. Therefore, thesecond letterspecifically represents thecirculation mechanism for the internal cooling medium.

The correct answer isC, NFPA 70. NFPA 70 is theNational Electrical Codeand it is the primary installation standard used for electrical wiring systems, includingsignaling and communications conductors, associated equipment, and raceways. In source inspection and quality surveillance, the inspector must verify that electrical equipment and its installation-related features are consistent with the applicable code requirements identified in the purchase documents and project specifications. For signaling and communications circuits, NFPA 70 provides the governing installation rules for conductor methods, separation, protection, routing, and raceway usage.

The other options do not fit this question.NEMA 250covers enclosure types and environmental protection ratings for electrical equipment enclosures, not installation rules for communications and signaling systems.IEEE C37.20.2applies to metal-clad switchgear, so it is equipment-specific and not the general installation code for communications conductors.IEC 20047is not the recognized answer in this context.

From an API source inspection perspective, this distinction matters because inspectors must know whether they are checkingequipment construction standardsorfield installation code requirements. For signaling and communications installations, the correct governing standard isNFPA 70.

The correct answer isA. Thesource inspection project planis the document that defines how inspection and surveillance will be carried out for a particular purchase order, package, or item of equipment so that the requiredquality expectations, contractual requirements, specifications, and critical inspection pointsare properly addressed. In practical API source inspection work, the plan establishes the scope of surveillance, identifies what documents will be reviewed, what hold or witness points will be observed, what tests will be witnessed, and how findings will be reported. Its purpose is therefore to giveproject-specific directionon how inspection activities will assure conformance to the purchaser’s requirements.

Option B is not the best answer because risk assessment may help determine the plan, but it is not the plan’s primary purpose. Option C is incorrect because inspector qualifications may be maintained elsewhere in personnel records and are not the core function of the project plan. Option D is also incorrect because safety and conduct expectations are general organizational requirements, not the main objective of the source inspection project plan. The plan is fundamentally abouthow inspection will be executed to verify quality.

The correct answer isCbecauseapparent powerin an AC electrical system is measured involt-amperes VA. Apparent power represents the total electrical power supplied to a circuit and is the combination ofreal powerandreactive power. Real power, which performs useful work such as turning a motor shaft or producing heat, is measured inwatts. Reactive power, which supports magnetic and electric fields in inductive or capacitive equipment, is measured invars. Apparent power is therefore the vector sum of these two and is expressed inVAor larger units such askVAandMVA.

The other options are incorrect for this reason.Mhosis a unit of conductance, not power.Varsmeasure reactive power only.Wattsmeasure true or active power only. In source inspection and quality surveillance of electrical equipment, understanding these distinctions is important when reviewing motor data sheets, transformer ratings, switchgear load data, and electrical test reports. Equipment such as transformers and generators are commonly rated inkVA or MVAbecause their thermal and current-carrying capability is tied toapparent power, makingvolt-amperesthe correct answer.

The correct answer isB. Theinterrupting ratingof electrical equipment is the maximumsymmetrical fault currentthat the device has been tested and certified tosafely interruptat its rated voltage and under specified conditions. In switchgear, circuit breakers, and related protective devices, this rating is critical because it confirms the equipment can open a faulted circuit without rupture, fire, excessive damage, or danger to personnel.

The term doesnotrefer to thepeakorcrestcurrent value. Peak or crest current is associated more closely withmomentary withstand,closing, orshort-circuit current peak effects, not the formal interrupting rating used for breaker application. It also does not mean ordinaryload current, because interrupting ratings are concerned with abnormal fault conditions rather than normal operating current.

From an API source inspection perspective, the inspector verifies that the nameplate data, test reports, and purchase specification all agree on the required interrupting capacity. If the interrupting rating is below the available fault current of the system, the equipment is unsuitable for safe service. Therefore, the correct definition is thesymmetrical current rating safely interruptible by the device.

The correct answer isD. Vibration Meter. A vibration meter is specifically intended to measuremechanical oscillations, usually in terms of displacement, velocity, or acceleration. In source inspection of large electrical equipment, especiallyelectric motors over 500 HP, vibration measurement is important because excessive vibration can indicate problems such as rotor imbalance, shaft misalignment, bearing defects, looseness, soft foot, resonance, or installation errors. Since the API source inspection guide covers surveillance and verification activities for major rotating electrical equipment, understanding the purpose of vibration-measuring instruments is directly relevant to factory testing, condition verification, and acceptance evaluation.

The other options are not correct for this function. Atachometermeasures rotational speed, not mechanical oscillation. Aspectroscopeis used for optical spectrum analysis and is unrelated to machinery vibration. Anoscilloscopedisplays electrical waveforms and can show signals from sensors, but it is not the primary instrument designed specifically to measure machine vibration in routine inspection practice. Therefore, the best answer isVibration Meter, because it directly measures the mechanical oscillatory behavior of equipment.

The correct answer isB. In source inspection practice, aninspection waiveris the formal permission to proceed past an identifiedhold pointwithout thesource inspector being present. A hold point is a stage in manufacturing, fabrication, testing, or final inspection where work is not supposed to proceed until the required witnessing or verification has been completed. If the inspector cannot attend, the purchaser or authorized party may issue a waiver so the manufacturer can continue without delaying production.

This is different from the other options. OptionAis too broad because an inspection waiver is not a blanket permission to proceed without any purchaser representative at any stage; it is usually tied to aspecific inspection point. OptionsCandDdescribe situations involvingnonconformance disposition or concession, not a waiver of inspection attendance. Those matters require technical review and authorization through the nonconformance process.

Within API-aligned source inspection, control ofhold points, witness points, documentation, and release authorityis a key part of the inspection process. Therefore, an inspection waiver is best defined aspermission to proceed without the source inspector present at a hold point, makingoption Bthe verified answer.

The correct answer isA. UnderAPI 541, the vendor is required to provide thecalculated data from the final witness testing within two weeks following completion of the testing. This requirement recognizes that some final witnessed test results, especially those involving calculated performance values, are not always fully available at the exact moment the physical test ends. The vendor may need additional time to review recorded measurements, perform the required calculations, validate the data, and assemble the final certified test package.

This timing requirement is important in source inspection because the witnessed test may produce bothdirectly observed readingsandpost-test calculated results. The source inspector confirms that the testing itself was properly performed and witnessed, while the final calculated package must still be submitted within the standard’s required period so the purchaser can verify guaranteed motor performance and compliance. The other options are not the best match for the API 541 wording. “Upon request” is too indefinite, “at time of final shipment” may be too late, and “immediately upon completion of testing” does not allow for the calculation and certification process. Therefore,two weeks following testingis the verified API 541 answer.

The correct answer isA, Class I Zone 0. In hazardous-area classification,Class Irefers to locations whereflammable gases or vaporsmay be present in the atmosphere. Under theZone system,Zone 0is the classification used where an ignitable concentration is presentcontinuously,for long periods, orfrequently enoughthat it must be assumed to exist during normal conditions. This is the most severe gas-vapor zone classification because the hazardous atmosphere is expected to be present as part of normal operation.

By contrast,Class I Zone 1applies where flammable gas or vapor is likely to be present in normal operation, but not continuously for long periods.Class I Zone 2applies where the hazardous atmosphere is not likely in normal operation and, if it does occur, it exists only for a short time.Class I Division 2is also a less severe classification under the Division system, not the continuous-presence category.

From an API source inspection perspective, correct hazardous-area classification is critical because it governs the acceptable protection methods, enclosure types, markings, and certification requirements for electrical equipment installed in those areas.

The correct answer isC. Arc flash PPE is required when a task exposes a worker to the possibility of anarc flash hazard, especially when testing or working onenergized conductors or circuit parts.Voltage testing in AC systemson energized equipment is a recognized task that can place the worker within the arc flash boundary, because probes, tools, or inadvertent contact can initiate an arcing fault. For this reason, proper arc-rated clothing and related PPE are required whenever the task assessment identifies arc flash exposure.

The other options describe tasks that are generally considered lower risk when performed under normal conditions. Work oncontrol circuits below 120 VACdoes not usually present the same arc flash risk level.Removing coverson properly installed wireways, junction boxes, and cable trays is not automatically an arc flash task unless it exposes energized parts and abnormal conditions exist.Insulated cable examination with no manipulation of the cableis also typically not treated as an arc flash exposure task.

From a source inspection and electrical safety perspective, the key principle is thatPPE selection is based on exposure to energized conductors and the likelihood of initiating an arc event, which makesCthe verified best answer.

The correct answer isD. In API 541, when a motor shaft is monitored usingradial vibration probes, the probe-observed shaft surface must meet a strictcombined runoutlimit so that the vibration reading reflects actual machine vibration rather than shaft surface irregularity, eccentricity, or electrical and mechanical runout effects. API 541 sets this limit at25% of the allowed unfiltered peak-to-peak vibration amplitude or 6.4 µm 0.25 mils, whichever is greater. This requirement is important because excessive runout can distort probe signals and produce misleading vibration data during shop testing and acceptance.

From a source inspection standpoint, this is a critical verification item during motor testing for large rotating equipment. If the shaft finish and probe track are not within the required runout limit, the vibration measurements cannot be relied on for acceptance decisions. The API guide includeselectric motors over 500 HPas a covered equipment category and emphasizes inspection and surveillance activities tied to applicable standards, testing, and verification of compliance during manufacture. Therefore,option Dis the correct API 541 requirement.

The correct answer isB, IEEE Std 112. IEEE 841 applies to severe-duty, totally enclosed squirrel-cage induction motors used in petroleum and chemical industry service, and when it refers toelectrical performance testing, the standard points toIEEE Std 112as the governing test method unless the purchase specification states otherwise. IEEE Std 112 is the recognized standard for defining methods to determine motor performance characteristics such as efficiency, losses, current, power factor, and related operating behavior during testing.

The other options are not the best answer for this question.NEMA MG-1is a broad motor standard covering design, construction, and application requirements, but it is not the primary referenced document for conducting electrical performance tests in this context.IEEE Std 117relates more to test procedures and acceptance considerations for certain motor categories, but not the default performance-test basis cited here.IEEE Std 522is associated with insulation testing of form-wound stator coils and windings, not overall motor electrical performance testing.

Therefore, for source inspection of large electric motors, the correct referenced performance-test standard isIEEE Std 112.

The correct answer isA, manufacturer. IEEE C57.12.00 requires that each transformer be provided with adurable metal nameplateattached by themanufacturer. This requirement exists because the nameplate is a permanent identification and rating record for the transformer. It contains critical information such as manufacturer identity, serial number, kVA rating, voltage ratings, frequency, impedance, cooling class, temperature rise, and other essential design and operating data. Since this information originates from the transformer design and production records, responsibility for affixing the plate belongs to the manufacturer, not to the owner, purchaser, or inspector.

From an API source inspection perspective, the nameplate is an important verification point during final inspection. The source inspector checks that the plate is present, permanently attached, legible, and consistent with the approved data sheet, purchase order, drawings, and test records. A missing, incorrect, or improperly marked nameplate can create traceability problems and may result in nonconformance. Therefore, the correct party responsible for affixing the durable metal nameplate is themanufacturer, makingAthe verified answer.

The correct answer isDbecause, in source inspection and procurement practice,client standardsare commonly included in or referenced by thepurchase orderto supplement generalindustry standards. Industry standards such as API, IEEE, NEMA, IEC, and NFPA establish broad technical requirements, but they often do not capture all of the purchaser’s project-specific expectations. Client standards fill that gap by adding requirements for materials, testing, documentation, preservation, coating, marking, data submission, inspection hold points, and deviations or concessions.

This is a key concept in API-aligned source inspection. The source inspector does not verify equipment only against generic published standards. The inspector must verify conformance to thepurchase order, project specifications, approved drawings, applicable codes and standards, and purchaser-specific requirements. In that framework, client standards are a normal supplement to industry standards. The other options are less appropriate.Supplier quality standardsandmanufacturing standardsare usually internal vendor documents, whilematerial test reportsare records of compliance, not governing standards. Therefore, the documents that typically supplement industry standards as part of a purchase order areclient standards, makingoption Dthe verified answer.

The correct answer isAbecauseinspectionis the activity specifically directed at identifying defects, nonconformities, damage, incomplete work, or deviations from specified requirements before the product is accepted and released for shipment or delivery. In the API source inspection context, inspection is a focused verification activity carried out during manufacturing and at final stages to confirm that the equipment conforms to approved drawings, purchase specifications, code requirements, and inspection and test plans. It is therefore the most direct process for finding product defects before handover.

Quality controlis broader than inspection. It includes inspection, testing, review of records, and other operational techniques used to verify product quality.Quality assuranceis even broader and more preventive; it focuses on the quality system, procedures, planning, and confidence that quality requirements will be met.Examinationis too general and is not the best formal answer in source inspection terminology.

From an API perspective, the source inspector’s practical role is to witness, verify, document, and report conformance and nonconformance. That makes inspection the primary defect-finding activity before delivery.

The correct answer isC. Source Inspector. In API source inspection practice, once a non-conformance report NCR has been issued and a disposition such as repair, rework, use-as-is, or reject has been approved, the responsibility forverifying that the approved disposition has actually been implemented on the productbelongs to theSource Inspector. This is consistent with the inspector’s core role in source inspection: to witness, verify, document, and report whether manufacturing and quality activities comply with the approved specifications, drawings, procedures, and disposition requirements.

TheVendor’s Quality Managermanages the supplier’s internal quality system and coordinates corrective actions, but is not the independent verifier for the purchaser’s inspection function. TheInspection Coordinatoradministers scheduling, communication, and inspection planning, yet does not normally perform the physical verification at the equipment level. TheManufacturing Engineermay define or support the technical correction, but implementation verification remains an inspection responsibility. Therefore, after NCR disposition is approved, theSource Inspectormust confirm through examination, records review, and where necessary witness of reinspection or retest that the disposition was properly carried out and closed.

The correct answer isD. Formedium-voltage circuit breakers over 1000 Vthat use astored-energy operating mechanism, a key safety and functional requirement is that the mechanism mustnot release the stored energy until it has been fully charged. This prevents incomplete closing or tripping operations, avoids unreliable breaker performance, and reduces the risk of mechanical damage or unsafe operating conditions. In other words, the breaker mechanism must include an interlock or control feature that blocks release of the spring or stored-energy system unless the charging cycle has been properly completed.

The other options do not express the required stored-energy mechanism function. Indicating control power availability may be useful, but it is not the defining requirement of the stored-energy mechanism itself. Detecting fault current is the job of protective relays and sensing devices, not the charging mechanism. Locating the position of the charging mechanism is not a required protective function. In API-aligned source inspection ofswitchgear, the inspector verifies mechanism operation, interlocks, test records, and compliance with the applicable standards and project specifications. Therefore, the required function is toprevent release of stored energy unless the mechanism is fully charged, makingoption Dthe verified answer.

The correct answer isA. In the API source inspection process, planned dates for events such as thepre-inspection meeting,key inspection points, witness or hold activities, and theanticipated shipping datemust be identified early so that everyone involved in the supply and inspection chain can coordinate their responsibilities. This includes the purchaser, supplier or vendor, source inspector, expediting personnel, quality representatives, and sometimes third-party test witnesses. Advance identification of these dates helps ensure that the right people, documents, and inspection resources are available at the right time and that critical manufacturing or testing stages are not missed.

OptionBsounds reasonable, but identifying dates in advance does not by itself guarantee that schedule and quality requirements will be met. OptionCis only part of the benefit, not the main reason. OptionDmay be a practical staffing advantage, but it is narrower than the overall project coordination purpose.

From an API guide perspective, source inspection is aplanned and coordinated activity, not a last-minute visit. Therefore, the main purpose of identifying these dates early is toallow coordination with all project members involved in the activity.

The correct answer isC. Aclamp meteris used to measureelectrical current externallywithout disconnecting the conductor or opening the circuit. It works by clamping around a conductor and sensing the magnetic field created by current flow, then converting that into a current reading. In practical inspection and test work, the instrument’spurposeis current measurement, not merely magnetic-field observation. That is why option C is the best answer.

Option A describes theoperating principlein a partial sense, but not the actual inspection purpose of the device. Options B and D are unrelated to clamp meters and instead refer to hazardous-area temperature classification concepts. In API-aligned source inspection and quality surveillance, proper use of electrical measuring instruments is essential when verifying test results, factory checkout activities, and equipment conformity. The guide emphasizes inspection and surveillance of electrical equipment categories such aselectrical systems, along with verification of testing and measurement activities as part of source inspection practice. Therefore, a clamp meter is correctly usedto externally measure current flowing through a conductor, makingoption Cthe verified answer.

The correct answer isA. Under API 541,totally enclosed machinessuch asTEFC, TEPV, TEWAC, and TEAACare required to have alow-point drain. This requirement exists because enclosed motors can accumulatecondensation or moistureinside the housing due to temperature changes, shutdown periods, ambient humidity, or cooling system operation. If that moisture is not removed, it can degrade insulation, promote corrosion, contaminate internal parts, and shorten motor life. The low-point drain provides a controlled path for accumulated liquid to escape from the lowest part of the enclosure.

The other options are not universally required for all these enclosure types. Aheat exchanger cooling fanmay apply only to certain cooling arrangements, not to every totally enclosed machine listed.Bearing RTDsmay be specified for monitoring on many large motors, but they are not the defining common feature identified by this question.Surge protectorsare auxiliary protective devices and are not the standard enclosure-related requirement here. In source inspection practice, the inspector should verify that the motor enclosure includes the requireddrain provisions, that they are properly located, and that they conform to the approved design and specification.

The correct answer isBbecause ANSI and IEEE requirements for control wiring that passes across hinged doors or panels in metal-enclosed switchgear emphasizemechanical flexibility, proper looping, securement, and suitable conductor stranding, not installation in a flexible non-metallic conduit with a separate grounding conductor as described in option B. The standard intent is to ensure that repeated opening and closing of doors does not damage the conductor strands or insulation, and that stress is not transmitted beyond the supported points. That is why optionsAandCreflect accepted requirements: the wiring must be flexible enough for repeated motion and arranged in a formed loop with proper securement. OptionDis also consistent with switchgear wiring practice, where conductor size and stranding class are specified to provide durability under mechanical movement.

OptionBadds conditions that are not the stated requirement for wiring across a hinge in ANSI/IEEE C37.20.2. In source inspection, this distinction matters because inspectors must verify wiring methods against the actual standard requirement rather than accept added but non-required installation details.

The correct answer isC. Aninsulation resistance testis performed by applying aDC test voltageto the insulation system and then measuring the resulting resistance value, typically inohms or megohms. In practical terms, it is often described as aspot testbecause the instrument, usually amegohmmeter, applies a selected DC voltage and checks the insulation’s resistance to leakage current at that point in time. This makes it a widely used diagnostic test for cables, motors, switchgear, control panels, and other electrical equipment.

OptionAis more closely related to insulation adequacy against transient overvoltage conditions, which is not the main definition of an insulation resistance test. OptionBdescribes issues that may influence insulation condition, but not the definition of the test itself. OptionDis closer to adielectric withstand or hi-pot concept, where the concern is the voltage insulation can tolerate, not the resistance value measured during the test. Therefore, the best and correct definition isa spot overvoltage test using applied DC voltage to measure insulation resistance, which makesoption Ccorrect.

The correct answer isA, power factor. In AC electrical systems, the phase relationship betweenvoltageandcurrentis an important indicator of how effectively electrical power is being used. Thecosine of the phase angle differencebetween voltage and current is called thepower factor. Mathematically, power factor expresses the ratio ofreal power, which performs useful work, toapparent power, which is the total power supplied to the circuit. When voltage and current are in phase, the cosine value is 1 and the power factor is unity. When they are out of phase due to inductive or capacitive effects, the power factor becomes less than 1.

From a source inspection and quality surveillance standpoint, understanding power factor is important when reviewing electrical test data, motor performance, transformer loading characteristics, and system efficiency information.Real poweris measured in watts,apparent powerin volt-amperes, andmhois a unit of conductance, so none of those terms define the cosine of the phase angle itself. Therefore, the correct technical term for this cosine relationship ispower factor.