NABCEP PV Installation Professional Exam
PV Output Circuit Maximum Current
# of parallel circuits x Isc x 1.25
Voltage Drop Equation
% drop =(0.2 x D x I x R )/V Where: D= one-way distance (in feet) I = current (nominal actual value, no 125% factors, use Imp for solar circuits) R = resistance of conductors (in ohms/1000ft) V = voltage (typical, nominal, use Vmp for solar circuits) Resistance values can be found in NEC Chapter 9 Table 8 "Conductor Properties"
How many volts does a common crystalline solar cell produce?
0.5 V
What size FMC conduit should be used for four size 6 AWG XHHW conductors, one size 8 AWG XHHW EGC and four 10 AWG THHN conductors? Only use the NEC code book to answer this question.
1-1/4" Use Chapter 9 Tables 4 and 5.
5 steps to calculating wire size
1. Calculate Maximum Circuit Current 2. Calculate the minimum overcurrent protection device 3. Calculate minimum conductor size based on Imax x 1.25 without conditions of use 4. Calculate minimum conductor size based on Imax with conditions of use 5. Determine if OCPD can protect the conductor under conditions of use.
Non-self-supporting ladders must be positioned at an angle where the horizontal distance from the top support to the foot of the ladder is _______ the working length of the ladder.
1/4
Stairs must have uniform riser height and tread depth with less than a _______ inch in variation
1/4
Rungs, cleats or steps on a ladder must be level and uniformly spaced between _______ and _______ inches apart.
10 ; 14
Peak sun
1000 W/m^2
Standard Test Conditions (STC)
1000 W/m^2 1.5 air mass 25 degrees Celsius
Standard Operating Conditions (SOC)
1000 W/m^2 Cell temp: NOCT
PVUSA Test Conditions
1000 W/m^2, 45 degrees Celsius, 1 m/s
What is the minimum busbar rating for a subpanel used as an inverter ac combiner panel to combine three 4000W, 240V single phase inverters?
125A Rating of each breaker = 16.7 X 1.25 = 25A Sum of inverter breakers = 3 x 25A = 75A Minimum size of back-fed breaker in main service panel = 3 x 16.7A x 1.25 = 62.2 --> 70A Minimum size busbars in subpanel x 1.2 = inverter breakers + utility breaker = 75A + 70A Minimum size busbars in subpanel = (75A + 70A)/1.2 = 121 --> 125A 705.12(D)(2)
OSHA requires that a stairway or ladder be used at points of access where there is an elevation break of _______ inches or more.
19
Where doors or gates open directly on a stairway, a platform must be used that extends at least ______ inches beyond the swing of the door.
20
Tall fixed ladders _______ feet or longer must be equipped with either: a ladder safety device; self-retracting lifelines with rest platforms every _______ feet of less ; or cage or well, and multiple ladder sections, each section not exceeding _______ feet.
24 ; 150 ; 150
Safety and Health Regulations for Constructions
29 CFR Part 1926 Subpart C - General Safety and Health Provisions Subpart D - Occupational Health and Environmental Controls Subpart E - Personal Protective and Life Saving Equipment Subpart I - Tools, Hand and Power Subpart K - Electrical Subpart M - Fall Protection Subpart X - Stairways and Ladders
When using a portable ladder for access to an upper landing surface, the side rails must extend at least _______ feet above the upper landing surface
3
Toe boards must be at least ______ inches tall
3-1/2
Safety nets must be deployed no further than ______ feet below where work is being performed
30
Stairway landings must be at least _______ inches deep and _______ inches wide at every _______ feet or less of vertical rise
30 ; 22 ; 12
Stairs must be installed between _______ and _______ degrees
30 ; 50
Guardrails must have top rails between ______ and ______ inches tall.
39 ; 45
Battery installations over ____lbs may have to meet certain engineering requirements in seismic regions for the design of non-structural electrical components (ASCE 7-10)
400
Unprotected sides of landings must have standard ______ inch guardrail systems
42
What is the maximum operating voltage of a battery system installed in a dwelling?
50 volts nominal
At what height is fall protection required?
6 ft
Nominal Operating Conditions (NOC)
800 W/m^2 Cell temp: NOCT
Nominal Operating Cell Temperature
800 W/m^2 Tair = 20 degrees Celsius PV Array: open-circuit Wind speed: 1.0 m/s
Grounded conductor
A current carrying conductor that is intentionally bonded to ground. It is the neutral conductor in any AC system.
Temperature compensation
A feature of charge controllers that automatically adjusts the charge regulation voltage for battery temperature changes.
Absorption charging
A finishing charge that occurs for a specified period after the regulation voltage is reached, usually for a few hours. Charging current continues to decrease throughout the absorption charge.
Sun path
A graphical representation of the sun's altitude and azimuth angles over a given day of the year.
Float charging
A maintenance charge that maintains the battery at a lower float voltage level and minimal current, essentially offsetting the battery self-discharge losses.
String
A series connection of PV devices.
Starting, lighting and ignition (SLI) battery
A type of battery designed for higher discharge currents, but are damaged by frequent and deep discharges.
Motive power or traction battery
A type of lead-acid battery designed for use in deep discharge applications.
Voltage Drop Limits
ASHRAE 90.1 Standards suggests no more than 3% of nominal voltage. NEC suggests no more than 5% in an "Informational Note". Sunpower standard is no more than 1%.
Rule of Thumb for Spacing Between Rows
Allow a space equal to three times the height of the top of the row or obstructions in front of the array. D = 3H
I-V curve
An infinite number of current and voltage operating point pairs for a PV device, at a given solar irradiance and temperature operating condition.
BOS
Balance-of-System Components include all mechanical or electrical components and hardware used to assemble and intergrate major components in a PV system together (i.e. all components in a PV system except modules and inverters)
Set points
Battery voltage levels at which a charge controller performs regulation or control functions. The proper regulation set points are critical for optimal battery charging and system performance.
BIPV
Building-Integrated Photovoltaics
Equation for Length of Shadow Cast by an Object
D = H x (cosA/tanE) Where: D = distance of shadow H = height of obstruction A = solar azimuth angle E = solar elevation angle
Diversionary charge controller
Diverts excess PV array power to auxiliary loads when the primary battery system is fully charged.
Solar radiation
Electromagnetic radiation ranging from about 0.25 µm to 4.5 µm in wavelength, including the near ultraviolet (UV), visible light, and near infrared (IR) portions of the spectrum.
Basic OSHA Requirements
Employers are required to provide a safe and healthful workplace free of hazards. All employers must display the OSHA poster and report to OSHA within 8 hours any incident that results in a fatality or hospitalization of three or more employees.
What is the leading cause of death in the construction industry?
Falls
List two types of valve-regulated lead-acid (VRLA) batteries
Gelled Absorbed Glass Mat (AGM) Have an immobilized electrolyte in gel form or absorbed in in fiberglass separator mats between the plates. VRLA batteries are spill sproof and do not require electrolyte maintenance. VRLA do not release gasses under normal charging and have lower ventilation requirements than flooded open vent types.
When is a charge controlled required?
If the maximum charge rates from the PV array multiplied by one hour is equal to 3% of the battery nominal amp-hour capacity or greater. 690.72
Multi-mode inverters
Inverters intended for use both in interactive and stand-alone applications.
UL1741
Inverters, converters, controllers and interconnection system equipment for use with distributed energy resources
Equalization charging
Is a periodic over-charge to help restore consistency among battery cells.
PV Source Circuit Maximum Current
Isc x 1.25 1.25 is to account for Increased Irradiance conditions.
JTA
Job Task Analysis The JTA outlines the expected duties of a qualified PV installation professional.
List four types of flooded lead-acid (FLA) batteries
Lead-Antimony Lead-Calcium Open-Vent Lead Calcium Sealed-Vent Lead-Antimony/Calcium Hybrid Have a liquid electrolyte solution. Open-vent flooded types have removable vent caps and permit electrolyte maintenance and water additions. Vented lead-acid batteries release hydrogen and oxygen gases, under normal charging conditions.
Battery charge controller
Limits the voltage and or current delivered to a battery from a charging source to regulate state-of-charge
Conduit Fill (i.e. Maximum Percent of Conduit Area Available for Conductors)
NEC Chapter 9 Table 1
NABCEP
North American Board of Certified Energy Practioners
Bulk charging
Occurs when the battery is below 90% SOC and all available PV current is delivered to the batteries. Battery voltage increases at the battery charges. Once the regulation voltage is reached, the charging current is limited to maintain regulation voltage.
Interactive PV systems
PV systems that operate in parallel with the electric utility grid.
Stand-alone PV systems
PV systems that operate independently of other electrical systems.
Bypass diode
Permit the flow of current in only one direction. They prevent cell overheating.
UL1703
Safety standard for flat-plate photovoltaic modules and panels
Solar insolation
Same as solar irradiation.
List two types of Nickel-Cadmium batteries
Sealed Sintered-Plate Flooded Pocket-Plate
Grounding electrode system
Several grounding electrodes effectively bonded together.
Solar ABC's
Solar America Board for Codes and Standards
Sizing EGC
The EGC should never be smaller than 14 AWG. Size the EGC according to Table 250.122
Maximum system voltage
The PV array open-circuit voltage at the lowest expected ambient temperature at a site.
Magnetic declination
The angle between magnetic North and the true geographic North Pole. Magnetic declination is considered positive when magnetic north is east of true north and negative when west of true north.
Array tilt angle
The angle between the array surface and the horizontal plane.
Peak Sun Hours (PSH)
The average daily amount of solar energy received on a given surface and is equivalent to the number of hour that the solar irradiance would need to be at a peak level of 1 kW/m^2.
Grounding electrode conductor (GEC)
The bare copper conductor connecting the system grounding bus to a ground rod or to the earth.
Low voltage disconnect (LVD)
The battery voltage set point at which the charge controller disconnects the system loads to prevent overdischarge.
Array azimuth angle
The direction an array surface faces relative to due South.
Solar azimuth
The direction of the sun's horizontal projection relative to a point on earth.
Solar declination
The ever changing angle between the earth's equatorial plane and the sun's rays.
Equipment grounding conductor (EGC)
The green or bare copper conductor linking exposed non-current-carrying metal parts of module frames, equipment and enclosures
Solar noon
The local time when the sun is at its highest point in the sky and crossing the local meridian (line of longitude).
Open-circuit voltage (Voc)
The maximum DC voltage on an I-V curve and is the operating point for a PV device with no connected load. Voc increases with decreasing cell temperature.
Inverter Output Circuit Maximum Current
The maximum continuous current rating listed on the product specification sheet.
Short-circuit current (Isc)
The maximum current on an I-V curve. Isc corresponds to a zero resistance and short-circuit condition, at zero voltage and zero power output. Short-circuit current is directly proportional to solar irradiance.
Regulation voltage (VR)
The maximum voltage set point the controller allows the battery to reach before the array current is disconnected or limited.
Autonomy
The number of days that a fully charged battery can meet system loads without any recharging.
Maximum power point (Pmp)
The operating point on an I-V curve where the product of current and voltage is at its maximum.
Solar window
The range of sun paths for a specific latitude between the winter and summer solstices
Specific gravity
The ratio of the density of a solution to the density of water. A fully charged lead-acid cell has a typical specific gravity between 1.26 and 1.28 at room temperature. Specific gravity may be increased in cold weather applications or decreased in warm weather applications to prolong battery life.
Air mass
The relative pass length of direct solar radiation through the atmosphere. Air mass affects the amount and spectral conect of the solar radiation reach the earth's surface and varies with sun position and altitude. AM 1.5 defines the spectral irradiance characteristic for testing and rating the electrical performance of PV cells and modules and is representative of a solar altitude angle of about 42 degrees. AM 0 is taken outside the earth's atmosphere and represents extraterrestrial radiation. When the sun is directly overhead in the tropics, air mass is equal to one (AM 1).
Grounding electrode
The rod or other buried electrode in the earth.
Solar altitude
The sun's elevation above the horizon.
Solar irradiation (solar energy)
The sun's radiant energy incident on a surface of unit area, commonly expressed in units of kWh/m^2. Solar irradiation is sometimes called solar insolation.
Solar irradiance (solar power)
The sun's radiant power incident on a surface of unit area, commonly expressed in units of kW/m^2
Array reconnect voltage (ARV)
The voltage set point at which the array is again reconnected to charge the battery. PWM and constant-voltage type controllers do not have a definable ARV
Load reconnect voltage (LRV)
The voltage that loads are reconnected to the battery.
When does minimal wind loading of a PV array occur?
When the array is mounted parallel to the roof surface at a height of 6 inches or less and at least three feet away from the edges of the roof.
Can single phase inverters be connected to 3-phase power systems?
Yes, as long as significant unbalanced voltages cannot result 705.100
Can an inverter output be connected to a subpanel instead of the main distribution panel?
Yes, see 705.12(D). But be careful that each panel in series meets the minimum busbar size requirements.
Stairways with _______ or more risers, or higher than _______ inches, must be equipped with at least one handrail capable of withstanding a force of _______ pounds
four ; 30 ; 200
If using ladders where the employee or the ladder could contact exposed energized electrical equipment, ladders must have ______________.
nonconductive side rails