Lesson 7

1) Why is the equipment ground necessary between the modules and the inverter? Can the same reason be used for installing the equipment ground between the inverter and the electric panel?

Answer: The equipment ground is installed to prevent unwanted currents from flowing causing equipment damage, personal injury, or even death given the right conditions when a person comes in contact with the equipmentís metal case.

2) Why is low-voltage power dangerous?

Answer: Low voltage causes the muscles to contract thereby it is possible that you canít let go. At higher voltages you can let go, and if the voltage is high enough it will burn itself away.

3) Does a PV module with an open circuit voltage and amperage of 27 and 3.5 respectively under full sun conditions present a shock hazard for someone who comes in contact with the wires? Explain your answer.

Answer: This situation is a serious shock hazard for anyone coming in contact with the wires. The voltage is high enough to overcome the skins resistance and the amp level is such that death could occur depending on the path between the wire contacts.

4) What is the function of the combiner box?

Answer: The combiner box is a device that allows individual electrical strings to be connected in parallel. The amp value of each string is added to produce one output with the ampere equal to the amp sum of the inputs.

5) Why is there disconnect switch between the inverter and the PV array?

6) Why is there a disconnect switch between the inverter and the buildingís electric panel?

Answer: To isolate the inverter from the utility, whenever the inverter is shutdown for repair of the inverter or any of the upstream portion of the PV system.

7) What are the two factors used to determine the size of wire to install in the PV system?

Answer: The current flow in and the length of the wire run.

8) Why is it important to evaluate the voltage drop in DC circuits?

Answer: Depending on the nominal voltage of the system, the voltage drop and associated line losses can be significant percentage of the systemís electrical output when using small gauge wires.

9) What three methods are commonly used to locate the rafter centers when on the roof?

Answer: Using the sounds of a hammer thumping the roof, using a stud finder, or looking at the fascia board/rafter interface.

10) Why mount the PV array at a level 3 to 4 inches above the roof?

Answer: Mounting at this level allows air circulation below the array that can cool the cool the modules and also allows rain to run off the roof.


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