Nuts & Volts
Ambient temperature, especially when cold
What formula can be used to find the maximum circuit current?
Isc x 1.25 = Max. Circuit Current
What is the main function of an inverter in a PV System?
Converts DC to AC electricity
What is bonding?
Connecting equipment to establish electrical conductivity / continuity
Calculate the maximum voltage of a REC 410W Alpha module installed in Seattle
52.79 V
(-7.2 - 25 = -32.2), then (-32.2 x -0.24% = 7.73%), then (1.0773 x 49.0 = 52.79)
According to NEC 690.7, what type of PV system is allowed the highest voltage?
Ground-mounts / carports (V limited only by equipment)
Why can we ignore the "125% factor" if a system uses an electrically-limited Electronic Power Converter?
The architecture of the equipment limits the amount of output current
How is the 120% rule used for interconnection?
When connecting via breaker, the allowable PV amperage is (Busbar Amps x 1.2) - Main Breaker Amps
What is the difference between Equipment Grounding Conductors (EGC) and Grounding Electrode Conductors (GEC)?
EGCs connect bonded metallic equipment together, and the GEC connects the system to the grounding electrode
Calculate the maximum voltage of a QCell Q.Peak Duo ML-G10+ 400W module installed in Spokane
50.46 V
When would professional engineering be necessary to calculate maximum voltage for a system?
When the system is ≥ 100 kW
Why might the current produced by a PV module be higher than its "nameplate rating"?
Supply-side taps can occur anywhere between what two pieces of equipment?
Net meter and main service disconnect
Name one other type of grounding conductor, besides the standard rod
Ufer (concrete-encased), buried metal water pipes, ground rings, metal support structures
Calculate the maximum source current for a 420W REC Alpha Pure-R module
11.11 A
What is a temperature coefficient?
It measures how changes in temperature alter the voltage of a module or system
How is output current calculated for a microinverter system?
Microinverter output current x # of parallel microinverters in circuit
What rule must be followed to land a PV breaker anywhere in a service panel?
"Total Sources ≤ Busbar Rating"
What conductor conditions make faults more likely?
Nicked/chafed/pinched wires, thermal expansion, water exposure, improper installation
Calculate the output circuit current for a branch of (9) IQ8M Enphase microinverters
12.15 A
Why might it be difficult to identify the temperature coefficient on a cut sheet?
There is no standard label for the temperature coefficient (but TkVoc is common), other data points have their own temperature coefficients, TkVoc can be listed as a percentage or as "V per °C"
What type of module does not have a standard multiplying factor for calculating source circuit currents?
Bifacial modules
Compare/contrast string inverters and microinverters and give an example of when you would recommend one system over another.
Microinverters: 1 inverter per module, MPPT at module level, good for multiple roof faces or differential shading, can be expensive to replace
String Inverters: Single inverter for whole system, flexible location, "field-tested" for longer, usually easier to service... but inverter failure means whole system is down
What is the difference between ground and arc faults?
Ground = Exposed +/- conductor touches metallic equipment bonded to ground
Arc = Current "jumps" across a high-resistance failure point in the circuit
Calculate the output current for a branch of (12) IQ7X-96 Enphase microinverters
15.72 A