22 Installation & Commissioning Practice Questions & Answers

1. 1. An installer is mounting an array on an asphalt-shingle pitched roof. Why is a listed flashing slipped under the shingle course above the penetration instead of simply sealing the hole with roofing sealant?

   • A.Because the flashing, not the fastener, carries array uplift into the rafter
   • B.Because water running down the roof must be shed over the flashing, not held by sealant✓ Answer
   • C.Because sealant alone is acceptable when the roof is under five years old
   • D.Because flashing is needed on tile and metal roofs but is optional on shingle

   A roof is watertight because each layer sheds water onto the layer below it, so the flashing must lie under the upper course and over the lower one and let water pass across its surface. Sealant at the deck is a secondary line of defense that shrinks and cracks with age; it can never replace shedding.

   Source: NABCEP PV Associate Job Task Analysis, installation of mounting structures and roof waterproofing with listed flashingsReport a problem with this question

2. 2. A roof attachment for a pitched-roof array is fastened through the roof sheathing but misses the rafter beneath it. What is the principal problem with leaving it that way?

   • A.The array will sit high at that point and shade the module directly above
   • B.The fastener will corrode much faster in sheathing than it would in framing
   • C.The attachment loses the ground path that framing lumber would provide to it
   • D.Sheathing alone cannot resist the uplift load that the attachment must carry✓ Answer

   Sheathing is a thin panel meant only to span between framing members, so a fastener set in it has very little withdrawal capacity. Wind uplift pulls the attachment straight out of the roof, and the design assumes the fastener is embedded in a rafter or truss.

   Source: NABCEP PV Associate Job Task Analysis, attachment of mounting structures to structural members; mounting manufacturer installation instructionsReport a problem with this question

3. 3. In a rail-mounted rooftop array, which sequence describes the path by which loads on a module reach the building structure?

   • A.Module frame to module clamp to rail to roof attachment to rafter✓ Answer
   • B.Module glass to junction box to rail to flashing to roof sheathing
   • C.Module frame to rail to roof decking to ceiling joist to exterior wall
   • D.Module frame to grounding conductor to rail to attachment to rafter

   Mechanical load travels from the module frame through the clamp into the rail, from the rail into the roof attachment, and from the attachment into the framing member. Every link in that chain must be rated for the load, and the grounding conductor and flashing carry no structural load at all.

   Source: NABCEP PV Associate Job Task Analysis, mounting structure components and structural load pathReport a problem with this question

4. 4. Wind across a pitched-roof array and snow accumulating on it stress the same load path in different ways. Which statement describes both correctly?

   • A.Neither adds load once the attachments are torqued, because the array is rigid
   • B.Wind mainly lifts the array away from the roof, while snow presses down on it✓ Answer
   • C.Wind presses the array onto the roof, while snow loads act mostly sideways
   • D.Both act downward, so only the compressive strength of the rail matters

   Air flowing over an array creates suction on its upper surface, so the governing wind case is uplift that tries to pull the array off the roof. Snow is a downward gravity load, which means the attachments and framing must be adequate in both directions.

   Source: NABCEP PV Associate Job Task Analysis, structural considerations including wind, snow and static versus dynamic loadsReport a problem with this question

5. 5. Aluminum rails and module frames grow and shrink measurably as roof temperature swings through the year. What is the correct installation response?

   • A.Pull all module leads taut so that they cannot swing during thermal cycling
   • B.Clamp every rail splice tight so that no movement can occur in the array
   • C.Set rails at maximum length on a cold day so they can only shrink later
   • D.Follow the manufacturer's splice-gap rules and leave slack in conductor runs✓ Answer

   Aluminum expands and contracts noticeably over the temperature range a roof sees, and that movement cannot be prevented by tightening hardware. Manufacturers specify splice gaps or thermal expansion joints, and conductors are left with slack so cycling does not put tension on terminations and connectors.

   Source: NABCEP PV Associate Job Task Analysis, mounting structure installation per manufacturer instructions; racking manufacturer thermal expansion guidanceReport a problem with this question

6. 6. A crew proposes to land a bare copper grounding conductor directly under an aluminum lug on a module frame. Why is that connection a defect?

   • A.Copper in direct contact with aluminum sets up galvanic corrosion at the joint✓ Answer
   • B.Aluminum lugs accept stranded wire only, never a solid conductor
   • C.Bare copper is not allowed on a roof because sunlight anneals it
   • D.Copper conducts less well than aluminum, so the joint would run hot

   Two dissimilar metals in contact with moisture form a galvanic cell, and the more active metal corrodes away at the interface. That raises resistance and can eventually open the equipment grounding path, which is why tin-plated lugs or listed bimetallic connectors are used to keep copper and aluminum apart.

   Source: NABCEP PV Associate Job Task Analysis, material compatibility and grounding and bonding methods for array hardwareReport a problem with this question

7. 7. A mounting manual specifies 20 ft-lb for the module clamp bolts. What is correct practice at each clamp?

   • A.Set a torque wrench to that value and tighten every bolt to it✓ Answer
   • B.Tighten by hand feel and then add a quarter turn for a margin
   • C.Apply the stated value to the end clamps only, not the mid clamps
   • D.Tighten with an impact driver until the clamp will not turn further

   A torque figure exists because an undertightened clamp or termination works loose and overheats while an overtightened one deforms the hardware or crushes the frame. The only way to reach a stated value reliably is a calibrated torque tool, and the value applies wherever the manual says it does.

   Source: NABCEP PV Associate Job Task Analysis, installation of equipment to manufacturer specifications including termination torqueReport a problem with this question

8. 8. A ballasted, non-penetrating array is proposed for a low-slope commercial roof. What does that approach fundamentally depend on?

   • A.The absence of wind at the site, since nothing anchors the array down
   • B.The installer's judgment on site, since ballast involves no engineering
   • C.The membrane's ability to bond the array to earth without a conductor
   • D.The roof's capacity to carry the added weight, confirmed by an engineer✓ Answer

   A ballasted system resists wind uplift and sliding with weight instead of fasteners, so it adds significant dead load to a roof that may have little spare capacity. A structural professional has to confirm the roof can carry it, and the ballast layout comes from a wind-engineered plan rather than from field judgment.

   Source: NABCEP PV Associate Job Task Analysis, ballasted low-slope mounting systems and structural reviewReport a problem with this question

9. 9. A roof penetration was sealed with caulk alone and no flashing was installed. What is the most likely long-term outcome?

   • A.The module above loses output as moisture collects on its back sheet
   • B.Nothing happens, provided the caulk is renewed at each annual inspection
   • C.Water enters slowly, rots the deck, and exposes a repair under the array✓ Answer
   • D.The fastener loosens within weeks because the caulk lubricates the threads

   Sealant is a consumable that shrinks, cracks and loses adhesion under UV and thermal cycling, so a caulk-only penetration leaks after a few seasons. The array hides the leak while sheathing and framing rot, and the eventual repair means removing modules, racking and roofing.

   Source: NABCEP PV Associate Job Task Analysis, roof considerations and waterproofing of array attachmentsReport a problem with this question

10. 10. Two rail sections are joined by a splice in a rooftop array. How is electrical continuity across that splice properly established?

    • A.By a bonding method the equipment is listed for, such as a listed splice or jumper✓ Answer
    • B.By bare copper wire wrapped and twisted around both rails at the joint
    • C.By the friction of the splice hardware, which is always sufficient
    • D.By a self-tapping sheet-metal screw driven through both rail sections

    Anodized aluminum surfaces are insulating, and friction or a random screw does not make a durable, repeatable bond through them. Bonding must be made by a component listed and tested for that purpose so the equipment grounding path stays continuous for the life of the array.

    Source: NABCEP PV Associate Job Task Analysis, grounding and bonding of array mounting systems using listed componentsReport a problem with this question

11. 11. Why are exposed array conductors secured up to the racking instead of being left to rest on the roof surface?

    • A.Conductors lying on a roof pick up static that trips the inverter offline
    • B.Loose conductors add wind load the roof attachments cannot safely carry
    • C.Roof contact exposes them to abrasion, standing water and added heat✓ Answer
    • D.Roof contact voids the module's electrical listing in every installation

    A roof surface is abrasive, ponds water after rain, and sits in the hottest air layer on the building. Conductors supported clear of it stay cooler and dry, and thermal movement no longer drags the jacket back and forth across grit.

    Source: NABCEP PV Associate Job Task Analysis, wiring best practices for support and protection of exposed array conductorsReport a problem with this question

12. 12. Exposed conductors in an array run in direct sunlight above a hot roof. What does that environment demand of the cable?

    • A.It must be rated for sunlight resistance and for wet, high-temperature use✓ Answer
    • B.It must be the same cable used indoors, which is rated for all locations
    • C.It must be spliced only with heat shrink, since connectors fail in sunlight
    • D.It must be white or light in color so that it reflects rather than absorbs

    Ultraviolet light breaks down ordinary insulation and rooftop heat accelerates the process, so array wiring uses conductors specifically rated as sunlight resistant, wet rated and rated for elevated temperature. Standard indoor building wire in that location cracks and eventually faults to the frame or rail.

    Source: NABCEP PV Associate Job Task Analysis, conductor properties including sunlight resistance, wet rating and temperature ratingReport a problem with this question

13. 13. A home-run conductor passes across the cut edge of a metal rail. What is the correct treatment?

    • A.Wrap the conductor with electrical tape where it crosses and move on
    • B.Route or protect the conductor so the edge cannot cut through its insulation✓ Answer
    • C.Leave it, because PV cable insulation resists any edge it rests on
    • D.Increase the conductor size so the extra copper resists the sharp edge

    Thermal movement and vibration make a cut metal edge act like a slow saw on insulation, and the result is a ground fault or a short between conductors. The fix is to reroute the conductor away from the edge or to fit edge protection such as a grommet or bushing; tape is not a mechanical barrier.

    Source: NABCEP PV Associate Job Task Analysis, protection of conductors from physical damage in array wiringReport a problem with this question

14. 14. Why must conductors entering a combiner or junction enclosure be provided with strain relief?

    • A.So that the enclosure can be opened without loosening any terminal screw
    • B.So that the conductors stay in the same order in which they were pulled
    • C.So that pulling and movement are taken by the fitting, not the terminals✓ Answer
    • D.So that the enclosure keeps its indoor rating once the wiring is done

    A strain relief fitting transfers any pull, wind movement or weight into the enclosure wall instead of into the screw terminals. Without it, repeated tugging loosens terminations, which raises resistance and creates a hot connection, and the cable entry also loses its weather seal.

    Source: NABCEP PV Associate Job Task Analysis, fittings, strain relief and enclosure installation practicesReport a problem with this question

15. 15. Module leads are left with a small service loop instead of being pulled tight. What does that loop accomplish?

    • A.It keeps conductor length equal across strings so the currents balance
    • B.It lets a module be unclamped and lifted for service without stressing leads✓ Answer
    • C.It coils the conductor so that it filters electrical noise from the inverter
    • D.It stores slack to reroute the array to a second inverter in the future

    A service loop provides the slack needed to unclamp a module and tip it up without putting tension on the junction box or the connectors. The same slack absorbs thermal expansion of rails and frames, so nothing is pulled tight on a cold night.

    Source: NABCEP PV Associate Job Task Analysis, wiring best practices including service loops and drip loopsReport a problem with this question

16. 16. Two PV connectors made by different manufacturers couple together and feel secure. Why is that connection still a defect?

    • A.They would have to be soldered after mating, which is impossible in the field
    • B.They form an unlisted mating pair, so contact and sealing are unproven✓ Answer
    • C.They always carry different current ratings, so string current must be halved
    • D.They will be of opposite polarity, so string voltages subtract instead of add

    Connectors are tested and listed as mated pairs, and brands differ in contact geometry, plating, spring force and seal design even when the housings latch. A mismatched pair can develop high contact resistance and let water in, which leads to heating, arcing and ground faults.

    Source: NABCEP PV Associate Job Task Analysis, PV connector compatibility and use of listed components as intendedReport a problem with this question

17. 17. Beyond using a matched pair, what matters when mating PV connectors in the field?

    • A.They must be coated with dielectric grease before every mating
    • B.They must be taped over once mated so that water is kept out
    • C.They must be pushed fully home until latched, and kept clean and dry✓ Answer
    • D.They must be mated only after the string has been landed at the inverter

    A connector that is not pushed in until its latch engages leaves the contacts partly mated, which concentrates current on a small area and causes heating and arcing. Dirt or moisture at the interface also prevents the seal from closing, so the contact area must be clean and dry before mating.

    Source: NABCEP PV Associate Job Task Analysis, field assembly and mating of PV connectors per manufacturer instructionsReport a problem with this question

18. 18. A grid-tied array is ready for start-up. Why is the DC side measured and verified before the inverter is placed in service?

    • A.Because a reversed or out-of-range string can damage the inverter as soon as it sees DC✓ Answer
    • B.Because utility approval is unnecessary when the DC side has been verified
    • C.Because DC conductors stay de-energized until the AC disconnect closes
    • D.Because the inverter cannot read DC voltage once its AC side is live

    Modules produce voltage whenever they are lit, so the DC circuits are already energized and cannot be switched off at the source. Confirming polarity and open-circuit voltage on every string before the inverter is energized prevents equipment damage and tells the crew what they are actually working on.

    Source: NABCEP PV Associate Job Task Analysis, commissioning sequence including string voltage and polarity verification before energizingReport a problem with this question

19. 19. What does an insulation-resistance test of a PV circuit reveal that an ordinary multimeter reading does not?

    • A.Whether the modules are connected in series rather than in parallel
    • B.Whether the insulation is damaged or wet enough to leak current to ground✓ Answer
    • C.Whether the conductors are large enough for the current of the string
    • D.Whether the string will reach its rated power at the present irradiance level

    An insulation tester applies a high test voltage between the circuit conductors and ground and measures the tiny leakage current that flows, which exposes damaged, pinched or wet insulation. A multimeter works at a few volts and will read normal on insulation that would break down under working voltage.

    Source: NABCEP PV Associate Job Task Analysis, commissioning tests and use of insulation-resistance test equipmentReport a problem with this question

20. 20. A string of 12 modules should read about 480 V open-circuit at the present conditions, based on roughly 40 V per module. The installer measures 400 V at the combiner. What is the most likely explanation?

    • A.The modules are wired in parallel, which lowers the voltage of the string
    • B.The irradiance is low, and string voltage falls in proportion to irradiance
    • C.The reading is normal, because 400 V is the value corrected to standard conditions
    • D.Two modules are not contributing, from a bypassed module or an open connection✓ Answer

    Voltage adds in series, so the 80 V shortfall at about 40 V per module points to roughly two modules not contributing, typically a bypassed module or an unmated connector. Irradiance mainly drives current, not voltage, so low light would not remove 80 V from the string.

    Source: NABCEP PV Associate Job Task Analysis, comparing measured string voltage against expected values during commissioningReport a problem with this question

21. 21. Why does a completed PV system carry durable labels at its disconnects and equipment?

    • A.So that the utility can bill the customer for the energy the array exports
    • B.So that a first responder or later technician can find and isolate sources✓ Answer
    • C.So that the modules keep their manufacturer warranty over the labeled life
    • D.So that the inverter can identify which circuits are tied to its output

    Labels exist to inform people who did not build the system: a firefighter arriving at night and a service technician arriving years later. They need to know that PV sources are present, where the disconnecting means are, and what stays energized in daylight after everything else is opened.

    Source: NABCEP PV Associate Job Task Analysis, labeling and marking of PV equipment for responders and service personnelReport a problem with this question

22. 22. The inspection has passed and the crew is ready to leave. What belongs in the handover package given to the system owner?

    • A.The crew's timesheets and the purchase invoices for the mounting hardware
    • B.The installer's tool list so that the owner can buy matching equipment
    • C.A signed statement that the owner accepts all future maintenance liability
    • D.As-built drawings, manuals, monitoring access and the shutdown procedure✓ Answer

    Handover is part of commissioning: the owner receives the as-built plan set, equipment manuals and warranty information, access to monitoring, and a walk-through of normal operation and emergency shutdown. The crew should also confirm that the utility has granted permission to operate before the system is left exporting.

    Source: NABCEP PV Associate Job Task Analysis, commissioning documentation, permission to operate and owner orientationReport a problem with this question

Practice questions based on the published knowledge domains of the NABCEP PV Associate Job Task Analysis and on standard photovoltaic engineering and safety references. NABCEP is not affiliated with this site and does not endorse it. Answers here deliberately avoid code dimensions, manufacturer specifications, incentive rules and prices, all of which change and vary by jurisdiction — always apply the electrical and building codes adopted by the authority having jurisdiction, the equipment manufacturer's instructions, and your employer's safety program. Confirm current exam requirements with NABCEP before testing. About the NABCEP Associate program →