Mixed Deck — All NABCEP Topics Flashcards

A grid-tied string inverter's display shows an 'Isolation Fault' error. This indicates:

Answer: The DC resistance between the PV array conductors and ground has dropped below the minimum threshold

An isolation fault means the impedance between ungrounded DC conductors and earth ground has fallen below the inverter's minimum threshold, indicating a potential ground fault in the array.

An employer wants to use a personal fall arrest system (PFAS) on a rooftop PV installation. The anchor point must be capable of supporting at least:

Answer: 5,000 lbs per worker attached

OSHA 29 CFR 1926.502(d) requires each personal fall arrest system anchor to support at least 5,000 pounds per worker attached.

During PV system commissioning, you measure an open-circuit voltage significantly higher than the STC-rated Voc. What is the most likely cause?

Answer: Ambient temperature is much lower than 25°C STC

PV module Voc increases as temperature decreases below 25°C STC, so cold conditions yield higher-than-rated Voc readings.

During an inspection, a technician finds that the AC output conductors from the inverter to the AC disconnect are 8 AWG THWN-2 copper rated at 50A, and the AC disconnect has a 60A fuse. The inverter's output circuit breaker is rated at 30A. Is there an issue?

Answer: Yes, the 60A fuse exceeds the conductor ampacity and must be replaced with a 50A fuse

The overcurrent device protecting a conductor must not exceed the conductor's ampacity; 8 AWG THWN-2 copper is rated for 50A, so the 60A fuse in the AC disconnect violates this requirement.

During troubleshooting, a technician suspects a failed bypass diode in a module. Which test method can confirm this without removing the module?

Answer: Use a clamp meter on each substring under load to check for anomalously low current through bypass diode paths

A shorted bypass diode creates an alternative current path; measuring current distribution with a clamp meter under load can reveal abnormal conduction through diode circuits.

What is the primary goal of regulatory compliance in solar energy installations?

Answer: To meet legal requirements and ensure safety.

The primary goal of regulatory compliance in solar energy installations is to ensure that all systems meet established legal requirements and safety standards. This adherence protects workers during installation, ensures the long-term safety of the public, and guarantees that the system operates efficiently and reliably according to industry benchmarks and environmental regulations.

What is the main advantage of a bifacial PV module compared to a monofacial module?

Answer: Ability to generate power from both front and rear surfaces

Bifacial modules capture direct irradiance on the front and reflected/diffuse irradiance on the rear, increasing total energy yield.

During a system inspection, you find that a microinverter AC branch circuit has 15 microinverters, each with a maximum output of 230VA. The branch circuit breaker is rated at 20A at 240V single-phase. Does this comply with NEC 705.12?

Answer: No, the output current of 14.4A exceeds 80% of the 20A breaker (16A) and must be on a 20A breaker after applying the 125% continuous load rule

Inverter output circuits are considered continuous loads, so the calculated load (14.4A) must not exceed 80% of the overcurrent device rating (16A for a 20A breaker); 14.4A is within the 16A limit, making this installation compliant.

Heat illness prevention for solar installers working outdoors in summer includes all of the following EXCEPT:

Answer: Requiring workers to wear dark-colored clothing

Dark clothing absorbs more heat; OSHA's heat illness prevention guidance recommends light-colored, loose-fitting clothing to reflect heat.

A PV module with a failed bypass diode that is NOT conducting will cause which condition during normal operation?

Answer: The affected cell group will develop excessive heat as a hot spot, potentially damaging the module

A non-conducting (open) bypass diode means shaded or underperforming cells must pass full string current, dissipating power as heat and creating damaging hot spots.

A string of 10 modules each with Voc of 40V is installed in a climate with a minimum design temperature of -10°F. Using the IEC 60364-7-712 method, if the voltage correction factor at -10°F is 1.25, what is the maximum string Voc?

Answer: 500V

Maximum Voc = 10 modules × 40V × 1.25 correction factor = 500V, which must not exceed the inverter's maximum input voltage.

A client reports that their newly commissioned 8 kW PV system is only showing 3.5 kW of production on their monitoring app at solar noon on a clear, cool day. The technician confirms the inverter is operating without errors and that DC string voltages and currents are normal. What is the most likely cause of the discrepancy?

Answer: The system's production monitoring current transformers (CTs) are installed incorrectly.

When the inverter is operating correctly with normal DC inputs and showing no faults, but the reported production is inaccurate, the issue often lies with the measurement equipment. Production monitoring CTs that are installed on the wrong conductors, facing the wrong direction, or not fully clamped can lead to significant under-reporting of system output. A tripped AC breaker would result in zero production. Reverse polarity or multiple failed diodes would cause abnormal DC voltage/current readings and likely trigger inverter faults.

What does the IFC require for PV system DC disconnect labeling when the disconnecting means is not within sight of the PV array?

Answer: A permanent plaque indicating the remote location of the disconnect

When the DC disconnect is out of sight of the array, IFC and NEC require a permanent plaque or directory on the remote disconnect indicating the array location.

How does shading affect solar panel performance?

Answer: Shading reduces energy production dramatically.

Shading significantly impacts solar panel performance because even partial shading on a single cell can dramatically reduce the output of an entire panel or string of panels. This is due to the series connection of cells; if one cell is shaded, it acts as a bottleneck, limiting the current flow for all other cells. Consequently, energy production can drop sharply, making shade avoidance critical for optimal system efficiency.

Before installing a rooftop PV system, the International Building Code (IBC) requires that the roof's structural integrity be verified. Which of the following is a mandatory requirement?

Answer: A structural analysis must be performed to confirm the roof can support the additional dead and live loads.

The IBC mandates that the building structure must be capable of supporting all imposed loads. For a PV installation, this requires a structural analysis, often performed by a licensed engineer, to verify that the existing roof can safely handle the added dead load of the PV system (modules, racking) as well as any applicable live loads like wind and snow.

In an AC-coupled battery storage system, the battery inverter connects to which bus?

Answer: The AC electrical panel or AC bus

In an AC-coupled system, the battery inverter connects to the AC bus, meaning solar energy is first inverted to AC before being re-converted to DC for battery charging.

During routine maintenance, a technician finds that an inverter's ground fault protection device (GFPD) has tripped. The safest next step is to:

Answer: Disconnect the array and inverter, then inspect wiring for ground faults before resetting

A tripped GFPD indicates a real or suspected ground fault; the system must be de-energized and inspected before resetting to prevent fire or shock hazard.

A ground-mount array is designed with row spacing to prevent self-shading at a specific 'design sun altitude.' Which sun altitude angle is the NABCEP standard practice for limiting inter-row shading in the continental US?

Answer: Solar altitude at 10 AM on the winter solstice (approximately the lowest critical sun angle)

NABCEP best practice uses the winter solstice at 10 AM (and 2 PM) as the design sun angle for row spacing to prevent self-shading during the period of lowest sun angles in the year.

Under OSHA's Eye and Face Protection standard, safety glasses used on a PV job site must comply with which ANSI standard?

Answer: ANSI Z87.1

OSHA requires eye and face protection to meet ANSI Z87.1, the standard for Occupational and Educational Personal Eye and Face Protection Devices.

What is the maximum allowable deflection for a rack mounting system under design load conditions per most structural standards?

Answer: L/240

Most racking standards require deflection not to exceed L/240 of the span under design loads to maintain structural integrity.