Section 8: PV Electrical Design Flashcards
How do you calculate maximum and minimum number of modules in a string?
For max: Use Voc and round down
For min: Use Vmp and round up
What do 3-Line diagrams do?
They show all the wires in a system
What is a single line diagram?
This is more like a flow chart
What are the 4 circuits in a pv system to remember?
PV source circuit: comes from modules toward combiner box
PV output circuit: after combiner box and combined into one circuit, heads to DC disconnect
Inverter input circuit: after DC disconnect, toward inverter
Inverter out circuit: after inverter, leads to AC disconnect, and then to main service panel
What conditions can lead to hot wires?
Hot ambient temperatures
Too many wires in conduit
Sunlight on conduit over rooftop
What are Over Current Protection Devices (OCPDs)?
Should open the circuit before the insulation fails.
Must be oversized to 156% of shot the short circuit current
What is ampacity?
The maximum current, in amperes, that a conductor can carry continuously under conditions of use without exceeding its temperature rating.
How much should inverters be oversized?
125% to account for higher production than test conditions
4 stages of battery charging?
Bulk - quick charge
Absorption - slow
Float - Top off the charge
Equalization - Controlled overcharge
Grounding vs Bonding
Grounding is the connection of a live electric source to the earth…provides return path from machine to power source
Bonding is the connection of two electrical conductors. Does not ensure protection.
What are the different types of grounding?
Grounded Conductor-White or Grey current carrying conductor to ground-often called neutral
Equipment Grounding Conductor-Green or bare wire that bonds all metal together. Not meant to carry current
Grounding electrode-metal that is connected to the earth
Grounding electrode conductor-Green/bare wire that connects electrode to system
What is single point system grounding?
Single point System Grounding-Only connect to earth in one spot to reduce risk of Ground Fault
What is 120% rule labeling?
Main breaker + 125% of inverter current does not exceed the busbar, but does exceed 100% of the busbar rating
What is the formula for calculating voltage drop over the length of a conductor?
Vd = Imp * (2 * distance * resistance in ohms)/1000 ft
Vd % = Vd/Vnom
Try to keep voltage drop under 2%
What is AHJ?
Authority Having Jurisdiction - city or country where plans are approved. AHJ interprets the meaning the NEC and other building codes.
