Renewable energy (PV & EV): Oklahoma Unlimited Electrical Journeyman Practice Questions

In one- and two-family dwellings, what is the maximum PV system dc circuit voltage the NEC permits?

Section 690.7 limits PV dc circuits to 600 V in one- and two-family dwellings and 1,000 V on or in other buildings.

Why is a PV string's maximum voltage figured at the lowest expected ambient temperature?

Section 690.7(A) corrects the rated open-circuit voltage for the lowest expected ambient temperature, because Voc increases as cell temperature falls.

The maximum current of a PV source circuit is calculated as the sum of the parallel modules' rated short-circuit currents multiplied by:

Section 690.8(A)(1) multiplies the short-circuit current by 125% to account for sunlight above standard test conditions; the conductor rule in 690.8(B) adds another 125% for continuous duty.

Before any adjustment or correction, PV circuit conductors must have an ampacity of at least what percentage of the maximum circuit current from 690.8(A)?

Section 690.8(B) requires 125% of the 690.8(A) maximum current; since that current already includes 125%, the combined factor on Isc is about 156%.

With PV rapid shutdown initiated, conductors outside the array boundary must be reduced to what level, and how fast?

Section 690.12(B)(1) limits controlled conductors outside the array boundary (1 ft from the array) to 30 V within 30 seconds of initiation.

How far from the PV array does the NEC place the array boundary used for rapid shutdown?

Section 690.12(B) defines the array boundary as 305 mm (1 ft) from the array in all directions.

For a one- or two-family dwelling, where must the PV rapid shutdown initiation device be located?

Section 690.12(C) requires the rapid shutdown initiation device for a one- or two-family dwelling to be at a readily accessible outdoor location, so firefighters can reach it.

How must the PV system disconnecting means be marked?

Section 690.13(B) requires each PV system disconnect to be permanently marked as the PV system disconnect or equivalent, with a warning where line and load may both be energized when open.

Where must the PV system disconnecting means be located?

Section 690.13(A) requires the PV system disconnecting means to be installed at a readily accessible location.

What is the maximum number of switches or circuit breakers the NEC allows to make up the PV system disconnecting means?

Section 690.13 allows the PV system disconnect to consist of not more than six switches or circuit breakers in a single enclosure or group of enclosures.

Ground-fault protection is required for dc PV arrays operating above which levels?

Section 690.41(B) requires dc ground-fault detection and interruption for PV system dc circuits exceeding 30 V or 8 A.

What does the NEC require for the exposed metal frames of PV modules and their support structures?

Section 690.43 requires exposed non-current-carrying metal parts of PV module frames, equipment and enclosures to be connected to an equipment grounding conductor.

Which PV system components must be listed or field labeled for the application?

Section 690.4(B) requires inverters, motor generators, PV modules, ac modules, dc combiners, dc-to-dc converters, rapid shutdown equipment, dc circuit controllers and charge controllers to be listed or field labeled.

A building has a PV system with rapid shutdown. Where must the rapid shutdown label generally be placed?

Section 690.12(D) requires a permanent rapid shutdown label at each service equipment location, or at an approved readily visible location, showing the location of the initiation devices.

A PV inverter backfeeds a panelboard through a breaker at the end opposite the main. Under the 120% rule, what must not exceed 120% of the busbar rating?

Under 705.12(B)(2), with the source breaker at the opposite end from the main, 125% of the power source output current plus the rating of the device protecting the busbar may not exceed 120% of the busbar ampacity.