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NABCEP PVDS practice questions

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Question 1PV system electrical design

Under NEC 690.7, how is the maximum PV system DC voltage for a residential system calculated when the record low ambient temperature is used?

  1. Add the inverter's AC output voltage to the string Voc
  2. Divide the module Voc at STC by the array's maximum power current
  3. Multiply the module Voc at STC by the temperature correction factor for the lowest expected ambient temperature Correct answer.
  4. Use the module Vmp at STC without any temperature adjustment

Explanation

NEC 690.7 requires correcting the module open-circuit voltage from its 25 °C (STC) value using the manufacturer's temperature coefficient and the lowest expected ambient temperature at the site. The corrected string Voc must not exceed the inverter's maximum DC input voltage. Using Vmp or ignoring temperature would underestimate the cold-weather voltage.

Question 2PV system electrical design

A string has 12 modules each with Voc at STC of 41.2 V and a Voc temperature coefficient of −0.30 %/°C. At a record low of −10 °C, what is the approximate corrected string Voc?

  1. 560 V
  2. 451 V
  3. 494 V
  4. 538 V Correct answer.

Explanation

The temperature difference from 25 °C is 35 °C, so the voltage rises by 35 × 0.30% = 10.5%. Module Voc becomes 41.2 × 1.105 ≈ 45.5 V, and 12 modules give about 546 V, closest to 538 V among the choices when rounding the coefficient application. The corrected value must be checked against the inverter's maximum DC input rating.

Question 3PV system electrical design

Which conductor sizing rule applies to PV source and output circuits under NEC 690.8?

  1. Only the inverter output current determines DC conductor ampacity
  2. Ampacity must be at least 125% of the continuous current, and the overcurrent device must also be rated at least 125% of that current Correct answer.
  3. Ampacity may be reduced to 80% of Isc because PV is intermittent
  4. Ampacity must equal exactly the module Isc at STC

Explanation

NEC 690.8 treats PV output as continuous, requiring conductors and overcurrent devices sized at 125% of the calculated maximum current. The maximum current itself is typically 125% of Isc for source circuits, so both factors may apply. This accounts for irradiance above STC and continuous duty.

Question 4PV system electrical design

A PV source circuit has modules with Isc of 9.8 A. Applying the 125% irradiance factor and the 125% continuous-load factor, what minimum conductor ampacity is required?

  1. 15.3 A Correct answer.
  2. 12.3 A
  3. 9.8 A
  4. 18.6 A

Explanation

The maximum current is 9.8 × 1.25 = 12.25 A, and conductor ampacity must be at least 125% of that, giving 12.25 × 1.25 ≈ 15.3 A. Both factors apply because PV output is continuous and can exceed STC irradiance. The selected conductor's ampacity after adjustment must meet or exceed this value.

Question 5PV system electrical design

What is the purpose of the equipment grounding conductor in a PV array mounting system?

  1. To provide a low-impedance fault path that allows overcurrent devices to clear a ground fault Correct answer.
  2. To increase the array's open-circuit voltage
  3. To bond the array to the utility neutral for voltage stabilization
  4. To carry normal operating current back to the inverter

Explanation

Equipment grounding bonds non-current-carrying metal parts so a fault produces a low-impedance path that trips the overcurrent protective device. It does not carry normal current. Proper bonding of module frames and racking is required by NEC 690.43.

Question 6PV system electrical design

In a PV system using a transformerless string inverter, which grounding arrangement is typical?

  1. The array is ungrounded, and only equipment grounding of frames and racking is provided Correct answer.
  2. The array positive conductor is bonded to the inverter chassis
  3. The array is solidly grounded at the negative conductor
  4. The array is grounded through a GFCI receptacle

Explanation

Transformerless inverters generally operate with ungrounded PV arrays, so only equipment grounding of exposed metal is required. Ground-fault protection is provided by the inverter's internal GFDI or residual current detection. Functional grounding of a current-carrying conductor is not used.

Question 7PV system electrical design

Which overcurrent protection consideration applies to PV source circuits when reverse current from parallel strings is possible?

  1. The inverter AC breaker protects the DC source circuits
  2. A series fuse rated per the module's maximum series fuse rating may be required to protect against reverse current Correct answer.
  3. Source-circuit fuses must be rated at the array's maximum system voltage divided by two
  4. No overcurrent device is ever needed on PV source circuits

Explanation

When three or more strings are paralleled, a fault in one string can draw reverse current from the others, so source-circuit overcurrent protection is required. The device must not exceed the module's maximum series fuse rating and must be rated for the system DC voltage.

Question 8PV system electrical design

What does the maximum series fuse rating marked on a PV module represent?

  1. The maximum current the module can produce at STC
  2. The fuse rating needed for the equipment grounding conductor
  3. The fuse required on the inverter AC output
  4. The largest overcurrent device permitted to protect that module from reverse overcurrent Correct answer.

Explanation

The maximum series fuse rating is the largest overcurrent protective device that may be used in series with the module for reverse-current protection. Exceeding it could damage the module. It is not related to AC output or equipment grounding.

Question 9PV system electrical design

Which factor most directly determines the minimum number of modules per string for a grid-tied string inverter?

  1. The number of parallel strings
  2. The array's physical tilt angle
  3. The inverter's minimum MPP voltage and the modules' hot-temperature Vmp Correct answer.
  4. The inverter's maximum AC current rating

Explanation

The string must produce enough voltage at high cell temperature to stay above the inverter's minimum MPP window. That is calculated using hot-temperature-corrected Vmp and the inverter's minimum MPP voltage. Tilt and parallel string count do not set the minimum series count.

Question 10PV system electrical design

A module has Vmp of 34.5 V at STC with a Vmp temperature coefficient of −0.45 %/°C. At a cell temperature of 65 °C, what is the approximate Vmp?

  1. 31.6 V
  2. 40.7 V
  3. 34.5 V
  4. 28.3 V Correct answer.

Explanation

The temperature rise is 40 °C, so the voltage drops by 40 × 0.45% = 18%. Vmp becomes 34.5 × 0.82 ≈ 28.3 V. This hot-temperature value is used to verify the string stays above the inverter's minimum MPP voltage.

Question 11PV system electrical design

Why is the inverter's maximum DC input voltage a critical design constraint?

  1. Because it limits the number of parallel strings only
  2. Because it sets the array's maximum power output in watts
  3. Because it determines the AC breaker size
  4. Because exceeding it at cold temperatures can damage the inverter's input components Correct answer.

Explanation

Exceeding the inverter's maximum DC input voltage, which occurs at the coldest expected temperatures when Voc is highest, can cause dielectric or component failure. Designers correct Voc to record low temperature to confirm compliance. It does not set power output or AC breaker size.

Question 12PV system electrical design

Which condition causes a PV module's open-circuit voltage to be highest?

  1. Low irradiance combined with high cell temperature
  2. High irradiance combined with high cell temperature
  3. Low irradiance combined with low cell temperature
  4. High irradiance combined with low cell temperature Correct answer.

Explanation

Voc rises with irradiance and also rises as cell temperature falls, so the maximum Voc occurs at high irradiance and low temperature. Cold, clear conditions are therefore the worst case for maximum system voltage. Designers use record low temperature with full irradiance.

Question 13PV system electrical design

A PV module's bypass diodes primarily serve which function?

  1. To prevent reverse current from flowing through shaded cells and reduce hot-spot heating Correct answer.
  2. To increase the module's open-circuit voltage
  3. To convert DC to AC within the module
  4. To regulate the module's output current to a fixed value

Explanation

Bypass diodes provide an alternate path around shaded or faulty cell groups so current from unshaded cells does not force reverse current through them, which can cause hot spots. They protect cells rather than converting power or regulating output.

Question 14PV system electrical design

Which NEC article section addresses rapid shutdown requirements for PV systems on buildings?

  1. NEC 705.12
  2. NEC 690.12 Correct answer.
  3. NEC 310.15
  4. NEC 250.122

Explanation

NEC 690.12 specifies rapid shutdown requirements, defining the controlled conductors and voltage limits within and outside the array boundary. The other sections address grounding, conductor ampacity, and interconnection, respectively.

Question 15PV system electrical design

Rapid shutdown requirements limit the voltage of controlled conductors outside the array boundary to what value within a specified time after shutdown initiation?

  1. 30 V
  2. 150 V
  3. 600 V
  4. 80 V Correct answer.

Explanation

NEC 690.12 requires controlled conductors outside the array boundary to be reduced to 80 V or less within 30 seconds of rapid shutdown initiation. This protects first responders from energized conductors. The array boundary itself has separate limits.

Question 16PV system electrical design

What is the primary function of a PV array combiner box?

  1. To convert DC power to grid-compatible AC power
  2. To track the sun and adjust array tilt
  3. To terminate and combine multiple source circuits and provide overcurrent protection and a disconnect point Correct answer.
  4. To store excess energy for nighttime use

Explanation

A combiner box collects multiple PV source circuits into a single output circuit and typically houses source-circuit fuses and a disconnect. It does not invert power, track the sun, or store energy. Properly rated DC devices must be used inside it.

Question 17PV system electrical design

Which wiring method is generally required for PV source circuits installed outdoors on a rooftop in exposed locations?

  1. Bare copper conductors supported by zip ties
  2. Untreated interior Romex cable
  3. PV-rated conductors in a sunlight-resistant raceway or listed PV wire Correct answer.
  4. Standard THHN conductors without sunlight resistance

Explanation

Exposed outdoor PV conductors must be listed for the application, typically PV wire rated sunlight-resistant and wet-location rated, installed in a suitable raceway or supported per code. Non-sunlight-resistant or interior-only wiring degrades and is noncompliant.

Question 18PV system electrical design

What is the purpose of calculating voltage drop in a PV source or output circuit?

  1. To ensure the array operates within the inverter's MPP window and to limit energy losses Correct answer.
  2. To determine the module's maximum series fuse rating
  3. To set the rapid shutdown voltage limit
  4. To size the equipment grounding conductor

Explanation

Voltage drop reduces the voltage delivered to the inverter, potentially pushing operation outside the MPP window and wasting energy. Designers typically target a small percentage drop, often around 2% or less on DC circuits. It does not set fuse ratings or grounding sizes.

Question 19PV system electrical design

A PV output circuit carries 24 A and runs 90 feet one way in copper conductors. Using a resistance of about 1.24 ohms per 1000 ft for the selected size, what is the approximate voltage drop at 400 V?

  1. 1.3 V
  2. 10.7 V
  3. 5.4 V Correct answer.
  4. 2.7 V

Explanation

Voltage drop equals 2 × length × current × resistance per unit length. Using 90 ft × 2 = 180 ft, 180/1000 × 24 A × 1.24 Ω ≈ 5.4 V. This is about 1.3% of 400 V, which is generally acceptable for a DC circuit.

Question 20PV system electrical design

In a supply-side connection of a PV system, where is the PV inverter output typically connected?

  1. To the equipment grounding busbar
  2. To a dedicated backfed breaker in the main load center
  3. To the utility service conductors ahead of the main service disconnect Correct answer.
  4. To a subpanel fed by a 60 A feeder

Explanation

A supply-side connection ties the PV system to the service conductors on the utility side of the main disconnect, so the PV output is not limited by the busbar rating. It requires a dedicated disconnect and utility approval. Load-side connections use a backfed breaker instead.

Question 21PV system electrical design

Under the 120% rule for a load-side PV connection, which relationship must hold for a panel with a 200 A busbar and 200 A main breaker?

  1. Main breaker plus PV breaker must not exceed 120% of the busbar rating Correct answer.
  2. PV breaker must equal the main breaker rating
  3. PV breaker alone must not exceed 120% of the busbar rating
  4. Main breaker must be reduced to 100 A regardless of PV size

Explanation

The 120% rule limits the sum of the main overcurrent device and the backfed PV breaker to 120% of the busbar rating. For a 200 A busbar with a 200 A main, the PV breaker is limited to 40 A. Reducing the main breaker or using a supply-side connection can allow more PV.

Question 22PV system electrical design

Which is a key function of the inverter's maximum power point tracking?

  1. To continuously adjust operating voltage and current to extract maximum module power Correct answer.
  2. To convert the array to a fixed 12 V output
  3. To balance the state of charge of batteries
  4. To disconnect the array at night

Explanation

MPPT algorithms vary the operating point to find the array's maximum power point as irradiance and temperature change. This maximizes energy harvest. It does not fix output voltage, perform nightly disconnection, or manage battery state of charge.

Question 23PV system electrical design

Why must PV conductors be sized with attention to the termination temperature ratings?

  1. Because conductor ampacity depends on insulation and termination temperature limits, and the lowest rating governs Correct answer.
  2. Because terminations determine the module's Voc
  3. Because higher temperature ratings always reduce ampacity
  4. Because termination ratings set the inverter's AC voltage

Explanation

Conductor ampacity is limited by insulation temperature rating and by the temperature rating of terminations, with the lowest applicable rating governing. Using a higher-rated conductor than the termination allows does not increase the permitted ampacity. This affects conductor selection in PV circuits.

Question 24PV system electrical design

Which practice best reduces the risk of arc faults in a PV array?

  1. Using listed connectors matched to the conductor and torquing terminations to manufacturer specifications Correct answer.
  2. Using undersized conductors to reduce cost
  3. Increasing string voltage beyond the inverter rating
  4. Removing equipment grounding to simplify wiring

Explanation

Matched, listed connectors and properly torqued terminations minimize loose or mismatched connections that cause series arc faults. Arc-fault circuit protection is also required by code. Exceeding voltage ratings, removing grounding, or undersizing conductors increases risk rather than reducing it.

Question 25PV system electrical design

A designer must choose between two inverters for a string whose corrected cold-temperature Voc is 590 V. Inverter A has a 600 V maximum DC input; Inverter B has a 550 V maximum DC input. What is the correct conclusion?

  1. Inverter B is acceptable because 590 V is close to 550 V
  2. Neither inverter is acceptable because 590 V exceeds both limits
  3. Either inverter is acceptable because Voc at STC is lower
  4. Inverter A is acceptable because 590 V does not exceed its 600 V limit Correct answer.

Explanation

The corrected cold-temperature Voc of 590 V must not exceed the inverter's maximum DC input voltage. Inverter A's 600 V limit accommodates it, while Inverter B's 550 V limit is exceeded. STC values are irrelevant because the cold-temperature correction governs.

Question 26PV system electrical design

A PV module's datasheet lists a temperature coefficient of Voc of −0.30 %/°C. Which design calculation uses this coefficient most directly?

  1. Determining the maximum power point current at the hottest expected cell temperature
  2. Determining the module's short-circuit current at standard test conditions
  3. Determining the fuse rating required for the PV output circuit
  4. Determining the maximum Voc at the coldest expected cell temperature for string sizing Correct answer.

Explanation

The Voc temperature coefficient quantifies how open-circuit voltage rises as cell temperature falls, so it is applied to the coldest expected temperature to find the worst-case maximum string voltage. That value is then compared with the inverter's maximum DC input voltage and with equipment voltage ratings.

Question 27PV system electrical design

A string inverter has a rated AC output of 7,600 W and the designer plans a DC array of 9,900 W at STC. What is the DC-to-AC ratio?

  1. 2.30
  2. 0.77
  3. 1.77
  4. 1.30 Correct answer.

Explanation

The DC-to-AC ratio is the array STC rating divided by the inverter AC rating: 9,900 ÷ 7,600 ≈ 1.30. This ratio describes how much the array is oversized relative to the inverter and drives clipping analysis.

Question 28PV system electrical design

Which quantity sets the minimum ampacity of a PV source circuit conductor under the NEC?

  1. The inverter's rated AC output current
  2. The module's Isc multiplied by 1.25 Correct answer.
  3. The array's maximum power point current divided by 1.25
  4. The module's maximum power point current multiplied by 1.25

Explanation

PV source and output circuits are sized at 125% of the short-circuit current, because Isc is the highest current the source can deliver and the 125% factor accounts for continuous duty and irradiance enhancement. The result is then compared with conductor ampacity after adjustment and correction factors.

Question 29PV system electrical design

A module has an Isc of 9.8 A and the design uses 1.25 × Isc for the source circuit. What minimum conductor ampacity does this yield before any adjustment factors?

  1. 12.3 A Correct answer.
  2. 19.6 A
  3. 9.8 A
  4. 7.8 A

Explanation

Multiplying 9.8 A by 1.25 gives 12.25 A, which rounds to about 12.3 A. This is the minimum ampacity the conductor must have before applying conditions-of-use corrections.

Question 30PV system electrical design

Which conductor color is commonly reserved for the grounded conductor in a PV system's AC output circuit?

  1. Green
  2. Red
  3. Black
  4. White or gray Correct answer.

Explanation

The NEC identifies white or gray as the grounded conductor, green as equipment grounding, and black/red as ungrounded circuit conductors. Correct identification matters for safe terminations and inspection.

Question 31PV system electrical design

What is the main purpose of a DC disconnect between a PV array and a string inverter?

  1. To limit the array's current to the inverter's maximum input rating
  2. To step up the array voltage to the inverter's optimum input
  3. To convert the array's DC output to AC
  4. To provide a means to isolate the inverter from the array for service and maintenance Correct answer.

Explanation

A DC disconnect provides a manual means to open the circuit so service personnel can work on the inverter or array wiring without energized DC present. It does not transform, invert, or current-limit.

Question 32PV system electrical design

Which array configuration is most likely to require string fusing when using a central inverter?

  1. A single string connected directly to the inverter
  2. Two parallel strings of modules with a high maximum series fuse rating
  3. A bipolar array with a single string per pole
  4. Three parallel strings of modules with a low maximum series fuse rating Correct answer.

Explanation

When three or more strings are connected in parallel, a faulted string can be backfed by the others, so string fuses are typically required unless the module's maximum series fuse rating is high enough to tolerate the combined current. Single-string configurations cannot receive reverse current from parallel strings.

Question 33PV system electrical design

Which IEEE standard is commonly referenced for interconnecting a PV inverter with an electric utility?

  1. IEEE 837
  2. IEEE 80
  3. IEEE 519 only
  4. IEEE 1547 Correct answer.

Explanation

IEEE 1547 addresses interconnection and interoperability of distributed energy resources with the utility grid, including voltage and frequency ride-through and anti-islanding. Designers reference it when specifying grid-support functions.

Question 34PV system electrical design

A string has a corrected maximum Voc of 540 V at the coldest expected temperature. The inverter's maximum DC input voltage is 600 V and its MPPT window tops out at 550 V. Which design conclusion is correct?

  1. The string exceeds the inverter's maximum DC input voltage
  2. The string is fully compatible with both the maximum input voltage and the MPPT window
  3. The string is within the inverter's maximum DC input voltage but its Voc exceeds the MPPT window Correct answer.
  4. The string voltage must be doubled to reach the MPPT window

Explanation

The 540 V cold-temperature Voc is below the 600 V absolute limit, so it is safe, but it is below the 550 V MPPT upper bound, meaning the array will operate outside the MPPT tracking range at cold temperatures. The designer should adjust string length or select a different inverter.

Question 35PV system electrical design

A designer is choosing between a string inverter with a wide MPPT window and one with a narrow window. Which array condition makes the wide window more valuable?

  1. An array with modules wired in a single series string
  2. An array with multiple orientations or significant row-to-row shading Correct answer.
  3. An array using microinverters
  4. An array with a fixed tilt and no shading

Explanation

Multiple orientations or partial shading produce mismatched string voltages and currents, so a wide MPPT window helps the inverter track the true maximum power point across varied conditions. Uniform fixed-tilt arrays show less benefit.

Question 36PV system electrical design

A rooftop array uses 10 AWG copper PV source conductors in an ambient temperature of 50 °C with a raceway exposed to sunlight. Which step is required before comparing conductor ampacity to the calculated current?

  1. Divide the table ampacity by the module's Isc
  2. Use the 90 °C column ampacity without correction
  3. Apply ambient temperature and conduit fill correction factors to the table ampacity Correct answer.
  4. Multiply the table ampacity by 1.25

Explanation

Table ampacities assume 30 °C ambient and specific fill conditions, so ambient temperature and conduit fill correction factors must be applied. The corrected ampacity is then compared with 1.25 × Isc.

Question 37PV system electrical design

A PV output circuit runs 120 feet one way at 18 A using 8 AWG copper with a resistance of about 0.778 ohms per 1,000 feet. What is the approximate voltage drop?

  1. 1.7 V
  2. 13.6 V
  3. 6.8 V
  4. 3.4 V Correct answer.

Explanation

Voltage drop equals 2 × length × current × resistance per foot. That is 2 × 120 × 18 × 0.000778 ≈ 3.4 V, or about 0.7% of a 480 V circuit. The factor of two accounts for the round trip.

Question 38PV system electrical design

Which condition typically produces the highest continuous current in a PV source circuit and should be considered in conductor sizing?

  1. Hot summer afternoons when module temperatures exceed 60 °C
  2. Nighttime with the inverter in standby
  3. Cold clear mornings with high irradiance and module temperatures near 20 °C Correct answer.
  4. Heavy cloud cover with diffuse irradiance

Explanation

Short-circuit current rises with irradiance and is slightly higher at cool module temperatures, so cold clear conditions with high irradiance produce the maximum current. Hot modules reduce current slightly, and darkness or clouds reduce it greatly.

Question 39PV system electrical design

A designer is evaluating a load-side PV connection to a 400 A panelboard with a 400 A main breaker. Under the 120% rule, what is the maximum PV breaker allowed if the busbar is rated 400 A?

  1. 400 A
  2. 200 A
  3. 80 A Correct answer.
  4. 480 A

Explanation

The 120% rule states that the sum of the main breaker and the PV breaker cannot exceed 120% of the busbar rating: 1.20 × 400 = 480 A, so the PV breaker cannot exceed 480 − 400 = 80 A. The PV breaker must also be located at the opposite end from the main.

Question 40PV system electrical design

A PV system uses a supply-side connection to a service with a 600 A service disconnect. Which requirement applies to the PV disconnect?

  1. It must be installed on the load side of the main service disconnect
  2. It must be rated at least 600 A to match the service
  3. It must be rated for the PV inverter's output current and marked as a PV system disconnect Correct answer.
  4. It must be a fusible switch with current-limiting fuses

Explanation

A supply-side connection is made ahead of the main service disconnect, so the PV disconnect is sized to the inverter output current rather than the service rating and must be clearly marked as part of the PV system. This connection method avoids the 120% busbar limit.

Question 41PV system electrical design

What is the purpose of equipment grounding in a PV array with an ungrounded (transformerless) inverter?

  1. To bond the positive and negative conductors together
  2. To establish the maximum power point reference voltage
  3. To provide a low-impedance fault current path that allows overcurrent devices to operate Correct answer.
  4. To carry the array's operating current back to the inverter

Explanation

Equipment grounding bonds non-current-carrying metal parts to create a low-impedance path so fault current trips the overcurrent device quickly. It does not carry normal operating current or bond the DC conductors together.

Question 42PV system electrical design

A module's maximum series fuse rating is 15 A and the array has four parallel strings each producing 10 A of Isc. Which statement is correct?

  1. Parallel strings do not create reverse current risk
  2. String fuses are unnecessary because the module fuse rating exceeds the string current
  3. The module fuse rating applies only to the inverter DC input
  4. A faulted string could receive 30 A from the other three strings, exceeding the 15 A fuse rating, so string fusing is required Correct answer.

Explanation

With four parallel strings, a faulted string can be backfed by the other three strings, producing about 3 × 10 = 30 A, which exceeds the 15 A maximum series fuse rating. String fuses are therefore needed to protect the module and conductors.

Question 43PV system electrical design

Which factor most strongly influences the choice between a string inverter and module-level power electronics for a roof with several orientations and a shaded chimney?

  1. The weight of the inverter enclosure
  2. The length of the AC interconnection to the utility
  3. The ability to perform MPPT per module or per group to limit mismatch losses Correct answer.
  4. The color of the module backsheet

Explanation

Module-level electronics perform maximum power point tracking per module or small group, reducing mismatch losses from shading and mixed orientations. String inverters track a whole string, so partial shading drags down the entire string.

Question 44PV system electrical design

Which is the most appropriate method for reducing the risk of ground faults in a PV array's DC wiring?

  1. Using listed connectors, proper strain relief, and protected routing to prevent conductor damage Correct answer.
  2. Reducing conductor ampacity to save cost
  3. Increasing the array's maximum system voltage
  4. Removing the equipment grounding conductor to eliminate fault paths

Explanation

Most DC ground faults originate from damaged insulation, loose connectors, or abrasion, so listed connectors, strain relief, and protected routing are the primary preventive measures. Ground-fault detection equipment is the backup.

Question 45PV system electrical design

A PV system has a maximum system voltage of 1,000 V and uses modules rated for 1,000 V. The designer wants to add a string that raises cold-temperature Voc to 1,050 V. Which conclusion is correct?

  1. The design is acceptable if the inverter is rated for 1,000 V
  2. The design is acceptable because the MPPT window is below 1,000 V
  3. The design exceeds the module and system voltage rating and must be revised Correct answer.
  4. The design is acceptable because Voc falls at cold temperatures

Explanation

The maximum system voltage rating of modules, conductors, and disconnects must not be exceeded under any expected condition, including cold-temperature Voc. A 1,050 V cold Voc exceeds the 1,000 V rating, so string length or module selection must change.

Question 46PV system electrical design

A designer compares two inverters for a string whose cold-temperature Voc is 590 V. Inverter A has a 600 V maximum input and a 500 V MPPT upper limit; Inverter B has a 600 V maximum input and a 550 V MPPT upper limit. Which choice is better and why?

  1. Inverter A, because its MPPT window is closer to the Voc value
  2. Inverter A, because a lower MPPT upper limit keeps the array cooler
  3. Inverter B, because its wider MPPT window keeps the array within tracking range at cold temperatures Correct answer.
  4. Inverter B, because its maximum input voltage is higher

Explanation

Both inverters share a 600 V maximum input, but Inverter B's 550 V MPPT upper limit is closer to the 590 V cold Voc, so the array will remain in the tracking range longer. Inverter A would push the array out of MPPT at cold temperatures.

Question 47PV system electrical design

A PV array is installed at 2,000 m elevation where ambient temperatures are low. Which correction most affects conductor ampacity in this location?

  1. Increased ampacity due to lower ambient temperature
  2. The assumption that irradiance is lower at altitude
  3. The use of 90 °C conductors without correction
  4. Altitude correction for reduced air density and heat dissipation Correct answer.

Explanation

At higher altitudes, reduced air density lowers the ability of conductors and enclosures to dissipate heat, so ampacity correction factors apply. Lower ambient temperature may partially offset this, but the altitude correction must still be evaluated.

Question 48PV system electrical design

A PV system uses a transformerless inverter with a grounded array frame. Which condition must be avoided to prevent a hazardous DC fault?

  1. Using listed DC connectors
  2. Grounding a current-carrying DC conductor at the array Correct answer.
  3. Installing a DC arc-fault circuit interrupter
  4. Bonding the array frame to the equipment grounding conductor

Explanation

Transformerless inverters are designed for ungrounded DC arrays, so intentionally grounding a current-carrying DC conductor creates an unexpected fault path and defeats the ground-fault detection scheme. The array frame is still bonded to equipment ground.

Question 49PV system electrical design

A designer is calculating voltage drop for a PV output circuit that will operate near the inverter's minimum MPPT voltage on hot days. Why is this condition important?

  1. Voltage drop increases the array current beyond the conductor ampacity
  2. Voltage drop reduces the array voltage further, potentially dropping below the MPPT window Correct answer.
  3. Voltage drop raises the array voltage above the maximum input rating
  4. Voltage drop has no effect on MPPT operation

Explanation

On hot days, module Vmp falls, and resistive voltage drop subtracts additional volts before the inverter terminals. If the combined reduction pushes the array below the MPPT lower limit, the inverter loses tracking and production drops.

Question 50PV system electrical design

Which combination of design values is needed to determine the minimum number of modules in a string for a grid-tied inverter?

  1. The inverter's AC output current and the service rating
  2. The inverter's MPPT minimum voltage, the module's hot-temperature Vmp, and the module's Vmp at STC Correct answer.
  3. The inverter's maximum DC input voltage and the module's cold-temperature Voc
  4. The module's Isc and the string fuse rating

Explanation

Minimum string length is set by the inverter's MPPT lower voltage limit and the module's Vmp at the hottest expected cell temperature, using the Vmp temperature coefficient. The STC Vmp provides the starting point for that calculation.