Nevada C-2G Photovoltaics Contractor Examination

A photovoltaic cell produces electricity primarily because photons absorbed in a semiconductor p-n junction:

• AFree electron-hole pairs that the built-in electric field separates into a usable current
• BHeat the junction until thermoelectric voltage appears across the metal contacts
• CSpin the module frame so magnetic flux cuts the interconnect ribbons
• DStore charge chemically in the encapsulant the way a battery stores ions

Standard Test Conditions (STC) used on a crystalline-silicon module nameplate are:

• A1000 W/m² irradiance, 25°C cell temperature, AM1.5 spectrum
• B800 W/m² irradiance, 20°C ambient, 1 m/s wind (NOCT)
• C1100 W/m² irradiance, 0°C cell temperature, AM0 space spectrum
• D1000 W/m² irradiance, 45°C cell temperature, AM1.0 spectrum

As crystalline-silicon cell temperature rises above 25°C while irradiance stays constant, the dominant electrical change is:

• AOpen-circuit voltage falls and maximum power usually falls
• BOpen-circuit voltage rises sharply and fill factor increases
• CShort-circuit current falls by about 0.4 percent per °C
• DMaximum-power voltage is unaffected because MPPT holds Vmp fixed

Twelve identical modules are wired as two parallel strings of six modules in series. Compared with one module, the array’s nominal string voltage and combined current are:

• AVoltage about 6 times and current about 2 times
• BVoltage about 12 times and current about 12 times
• CVoltage about 2 times and current about 6 times
• DVoltage unchanged and current about 12 times

If plane-of-array irradiance drops from 1000 W/m² to 500 W/m² at the same cell temperature, the most accurate statement is:

• AIsc falls by about half and Voc falls only a little
• BVoc falls by about half and Isc stays nearly constant
• CBoth Voc and Isc fall by about half
• DBoth Voc and Isc stay at nameplate because voltage is fixed by the inverter

Bypass diodes in a crystalline-silicon module junction box are installed mainly to:

• ALimit reverse-bias heating of shaded cells and preserve most of the string current
• BBlock nighttime reverse current from a battery into the array
• CRaise Voc so fewer modules are needed to reach inverter minimum voltage
• DBond the module frame to the equipment grounding conductor

An inverter’s maximum-power-point tracker (MPPT) is intended to:

• AOperate the array near the Vmp/Imp point where the product of voltage and current is high…
• BHold the array at Voc so string voltage always stays at the 690.7 maximum
• CShort the array to Isc so conductor ampacity can be measured continuously
• DReplace the need for temperature-corrected string voltage calculations

NEC 2017 690.13(B) requires each PV system disconnecting means to be permanently marked:

• APV SYSTEM DISCONNECT or equivalent
• BSERVICE DISCONNECT ONLY
• CINVERTER INPUT — DO NOT OPEN
• DUTILITY METER BYPASS

NEC 2017 690.13(A) requires the PV system disconnecting means to be installed:

• AAt a readily accessible location
• BOnly on the roof within 1 ft of the array boundary
• CInside a locked inverter enclosure that requires a special utility key
• DOn the load side of every branch-circuit breaker in the dwelling

Under NEC 2017 690.13(D), each PV system disconnecting means shall consist of not more than:

• ASix switches or six sets of circuit breakers, or a combination of not more than six, in a…
• BTwo switches mounted in separate buildings
• CTwelve breakers if they are all backfed listed breakers
• DOne fused pullout plus any number of inverter-integrated switches

A PV dc disconnect can remain energized on both line and load terminals when open. NEC 2017 690.13(F) requires a warning that:

• AElectric shock hazard — terminals on the line and load sides may be energized in the open…
• BThe enclosure is suitable for use as service equipment only
• CRapid shutdown has already reduced every conductor to 0 V
• DThe disconnect may be used as the grounding electrode conductor splice

NEC 2017 690.15 isolating devices for inverters, fuses, and dc-to-dc converters differ from the 690.13 PV system disconnect because isolating devices:

• AAre required so equipment can be isolated from ungrounded conductors and are not required…
• BMust have an interrupting rating equal to the available fault current and must be load-br…
• CReplace the need for any PV system disconnecting means on interactive systems
• DMust be located only at the utility meter socket

A 200 A panelboard with a 200 A main breaker will receive a load-side PV connection at the opposite end of the bus from the main. Using NEC 2017 705.12(B)(2)(3)(b), the largest 125 percent of inverter output-circuit current that may be added is:

• A40 A
• B20 A
• C50 A
• D200 A

If a load-side PV breaker is installed at the same end of the busbar as the main breaker, NEC 2017 705.12(B)(2)(3)(a) requires that 125 percent of inverter output current plus the main OCPD:

• ANot exceed 100 percent of the busbar ampacity
• BNot exceed 120 percent of the busbar ampacity
• CNot exceed 125 percent of the busbar ampacity
• DBe ignored because same-end connections have no busbar limit

A supply-side (line-side) PV interconnection is permitted by NEC 2017 705.12(A) and 230.82(6) provided, among other things, that:

• AThe PV tap is made on a branch-circuit lighting panel in the garage
• BThe inverter output breaker is installed at the opposite end of a load-side bus using the…
• CThe disconnect is listed or field labeled as suitable for use as service equipment where…
• DNo overcurrent device is installed on the PV conductors

NEC 2017 705.31 requires overcurrent protection for a supply-side connected power-production source to be located:

• AAnywhere on the property if the conductors are 6 AWG or larger
• BOnly inside the interactive inverter
• CWithin 3 m (10 ft) of the point where the power-source conductors connect to the service
• DAt the opposite end of the service-entrance cable from the meter

NEC 2017 705.40 requires an interactive inverter to do which of the following if the utility primary source is lost?

• AContinue to export rated current to keep the neighborhood energized
• BClose a utility-side contactor and become a stand-alone service
• CAutomatically de-energize its output to the primary-source conductors (anti-islanding)
• DRaise dc input voltage to the 690.7 maximum to ride through the outage

A load-side PV interconnection in a panelboard must use a dedicated overcurrent device and disconnect. Which installation violates NEC 2017 705.12(B)?

• AA listed backfed breaker, identified as the PV point of interconnection, installed at the…
• BA fused ac disconnect ahead of a feeder tap that is then protected per 705.12(B)(2)
• CA clamp-on tap with no overcurrent device, landed on the panelboard bus stabs beside exis…
• DA breaker that is secured in place where the panel listing requires backfed breakers to b…

A 240 V interactive inverter will backfeed a 200 A, 200 A-main panel at the opposite end of the bus. Using NEC 2017 705.12(B)(2)(3)(b), the largest continuous inverter output current that complies is:

• A24 A
• B40 A
• C32 A
• D48 A

NEC 2017 705.12(B)(2)(3)(d) permits the 120 percent busbar calculation on a center-fed panelboard only when:

• AThe panelboard is in a one- or two-family dwelling and the PV breaker is on the opposite…
• BThe panelboard is any commercial 480 V switchboard
• CThe main breaker is removed and the panel is used as service equipment
• DMore than six PV breakers share the same bus

NEC 2017 690.54 requires a permanent label at the interactive-system point of interconnection stating:

• AOnly the module manufacturer and the C-2G license number
• BThe utility transformer kVA and the service grounding-electrode resistance
• CRated ac output current and the nominal operating ac voltage
• DThe array tilt, azimuth, and expected annual kWh

An inverter used to interconnect with NV Energy’s distribution system must be:

• AAny dc-to-ac converter, including an unlisted automotive inverter
• BBuilt on site by the C-2G contractor from a transformer and bridge rectifier
• CListed and identified for interactive operation (typically UL 1741) and compatible with I…
• DRated only for stand-alone cabins with no utility connection

Where a PV system disconnect is connected on the supply side of the service disconnecting means, NEC 2017 690.13(C) requires that disconnect to be:

• AA snap switch listed only for 15 A lighting loads
• BA non-fused molded-case switch with no interrupting rating
• CListed as suitable for use as service equipment
• DInstalled only on the roof next to the array

NEC 2017 705.10 requires a permanent plaque or directory, at service equipment and at each power-production disconnect, that shows:

• AThe location of all electric power-source disconnecting means on the premises
• BOnly the utility account number
• CThe manufacturer’s flash-test current for each module
• DThe contractor’s bid price for the array

Per NEC 2017 690.8(A)(3), the maximum current of an inverter output circuit is:

• AThe inverter’s peak surge current for 100 ms
• B125 percent of the array Isc regardless of ac rating
• CThe inverter’s continuous output-current rating
• DThe service-entrance conductor ampacity

A 7.6 kW, 240 V interactive inverter has a continuous output of 7600 / 240 = 31.7 A. The smallest standard breaker that meets NEC 2017 690.9(B) (125 percent of 690.8(A) current) is:

• A30 A
• B35 A
• C40 A
• D50 A

A listed backfed breaker used as the load-side PV point of interconnection must be:

• AInstalled in a multiwire lighting slot shared with a kitchen small-appliance breaker
• BRated 15 A regardless of inverter current so it trips first
• CTapped onto the panelboard neutral bar with no ungrounded-conductor protection
• DA dedicated overcurrent device identified as the PV interconnection, located where 705.12…

Under NAC 624.200, a C-2G photovoltaics license authorizes installation of PV cells, batteries, and inverters, but does not authorize:

• ARepair of an inverter that converts solar energy into electricity
• BReplacement of a failed PV module on an existing residential array
• CInstallation of a listed battery used with the PV system on the customer side of the serv…
• DInstallation, alteration, or repair of electrical wires beyond the service panel

NAC 624.200 further limits C-2G work to residential and commercial installations that are:

• AScaled or intended solely for the commercial production and sale of electricity
• BOff-grid systems only, with no utility interconnection allowed
• CUtility transmission substations operated by NV Energy
• DNot scaled or intended solely for the commercial production and sale of electricity

NV Energy Rule 15 generally requires the producer to furnish a manual ac disconnect that:

• AIs hidden in an attic and operable only with a manufacturer laptop
• BMust be a dc-only rooftop isolator with no ac contacts
• CIs required even for a listed non-islanding inverter of 0.5 kVA
• DProvides a visible open, is accessible to utility personnel, and can be locked in the ope…

After a grid-tied C-2G system passes local inspection, the contractor should energize and export to NV Energy only when:

• AThe modules first come off the truck
• BThe building permit application has been filled out but not submitted
• CThe homeowner flips the inverter on to “test” production for a weekend
• DThe utility has issued Permission to Operate (PTO) and required metering is in place

Before installing a rooftop PV system on a Nevada building, the C-2G contractor must typically obtain:

• AOnly a verbal go-ahead from the homeowner’s neighbor
• BAn NSCB waiver that eliminates all inspections
• CA federal generation license from FERC for every 6 kW dwelling system
• DThe local building/electrical permit (AHJ) and a utility interconnection application

A complete C-2G permit and interconnection package almost always includes which drawing as the electrical roadmap?

• AA landscaping planting schedule
• BA blank sheet labeled “as-built later”
• CA kitchen cabinet elevation
• DA one-line (single-line) diagram showing modules, inverter, disconnects, OCPD, grounding,…

The usual Nevada close-out sequence for a utility-interactive rooftop PV system is:

• AExport first, then apply for the permit, then call for inspection
• BFinal inspection only if the homeowner complains
• CUtility PTO first, then hide the work from the building department
• DPermit and interconnection approval, install, AHJ inspection, utility meter/PTO, then com…

On a PV module nameplate, Voc, Isc, Vmp, Imp, and Pmax are used in design as follows:

• AVoc and Isc are normal operating setpoints; Vmp is only a factory curiosity
• BPmax is the 690.7 maximum system voltage
• CIsc is the inverter ac output current
• DVoc is the 690.7 voltage extreme, Isc is the 690.8 current starting point, and Vmp/Imp/Pm…

Compared with a string inverter, a microinverter at each module typically:

• AConverts that module’s dc to ac at the array and keeps high-voltage dc from homerunning a…
• BRequires a 1000 V dc combiner and a central inverter in the garage
• CCannot comply with rapid shutdown because ac is more dangerous than dc
• DEliminates the need for any ac overcurrent device at the interconnection

A module-level power optimizer (dc-to-dc converter) is used on a string-inverter array primarily to:

• AConvert each module directly to 240 V ac for the service panel
• BIncrease nameplate Voc so fewer modules are allowed by 690.7
• CReplace the equipment grounding conductor on the module frames
• DPerform module-level MPPT and, when listed for the purpose, help the array meet 690.12 ra…

A dc combiner box on a multi-string array is used to:

• AConvert dc to ac before the inverter
• BReplace the grounding electrode system required by 690.47
• CServe as the utility visible-break ac disconnect
• DParallel PV source circuits, often with string overcurrent devices, into a PV output circ…

For a battery-based PV array, an MPPT charge controller is generally preferred over a PWM controller because it:

• AOperates the array near Vmp and can harvest more energy when array voltage is above batte…
• BAlways charges by shorting the array to Isc
• CRemoves the need for any battery disconnect or charge-control listing
• DConverts the array directly to 240 V ac

NEC 2017 690.31(C) permits which single-conductor cables in exposed outdoor locations for PV module interconnections within the array?

• AType NM-B (Romex) stapled across the shingles
• BUnmarked automotive primary wire
• CType SPT-2 lamp cord
• DType USE-2 and PV wire (photovoltaic wire)

NEC 2017 690.33 requires readily accessible PV connectors operating at over 30 V dc to be latching or locking and to:

• AOpen with a bare pull of the cable jacket while under load
• BServe as the only equipment grounding conductor for the module frames
• CBe made of unmarked dissimilar brands mixed freely in one string
• DRequire a tool for opening, or be rated for interrupting current

PV modules, inverters, combiners, and charge controllers used on a C-2G system must be:

• AIdentified and listed for the PV application per NEC 2017 690.4(B)
• BAccepted if they “look industrial,” even without a listing mark
• CBuilt on site from unlisted power-supply modules
• DListed only to a marine ignition-protection standard

Most modern transformerless string inverters operate the PV array as:

• AA solidly grounded 2-wire circuit with a white grounded conductor bonded at the inverter
• BAn unlisted battery charger with no ground-fault protection
• CA 480 V corner-grounded delta service
• DA non-isolated or functionally grounded array in which both dc circuit conductors are ung…

NEC 2017 690.12(D) requires equipment that performs rapid-shutdown functions, other than ordinary listed disconnects used only as initiation devices, to be:

• AField-fabricated from a lighting contactor and a doorbell transformer
• BOmitted on all rooftop arrays after January 1, 2019
• CAny unlisted optimizer as long as the installer labels it “RSD”
• DListed for providing rapid-shutdown protection

Flooded lead-acid batteries used with a PV system typically require more attention to which installation condition than sealed lithium iron-phosphate batteries?

• AVentilation for hydrogen gas and electrolyte spill/corrosion control
• BA battery management system that is never used on lithium batteries
• COperation only at 1000 V dc string voltage
• DInstallation outdoors with no disconnecting means