14.1 Solar Photovoltaic Systems, Energy Storage & EV Charging

14.1 Solar Photovoltaic Systems, Energy Storage & EV Charging

Modern electrical installations increasingly integrate renewable power generation, electrochemical storage, and high-capacity electric vehicle charging infrastructure. For the Kentucky Journeyman Electrician examination, candidates must master the precise safety, sizing, and disconnection rules found in NEC Article 690 (Solar Photovoltaic Systems), NEC Article 706 (Energy Storage Systems), and NEC Article 625 (Electric Vehicle Power Transfer Systems). These articles introduce specialized direct-current (DC) arc-hazard mitigation, rapid shutdown protocols to protect emergency first responders, battery isolation controls, and continuous load branch circuit requirements.

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1. Solar Photovoltaic (PV) Systems: NEC Article 690

Article 690 covers solar photovoltaic electrical energy systems, including array circuits, inverters, charge controllers, and storage interfaces. Because photovoltaic modules generate DC power whenever illuminated, PV source and output circuits cannot be turned off merely by opening a standard AC breaker. Special protection and shutdown controls are essential.

DC Arc-Fault Circuit Protection (NEC 690.11)

Direct-current arcs do not cross a periodic zero-voltage point like alternating current, making DC arcs self-sustaining and capable of generating severe thermal energy. Under NEC 690.11, photovoltaic systems operating at 80 volts DC or greater between any two conductors must be protected by a listed DC arc-fault circuit interrupter (AFCI), PV type, or other system components listed to provide equivalent protection.

Points to know about 690.11:

• What it detects: PV arc-fault protection is aimed at series arcs in dc circuits, such as loose module connectors, poor crimps, or damaged conductor terminations.
• What it does: When it detects an arc, the listed device or system interrupts the arc, typically by stopping the inverter or dc-to-dc converter from operating. How it does so, and how it indicates and resets afterward, is set by the product's listing (UL 1699B), not by detailed NEC rules. Older NEC editions (2011 and 2014) required manual restart and visual indication; current editions leave those details to the listing.
• Exception: Certain PV dc circuits that are not installed on or in buildings and are run in metal raceways, metal-clad cable, enclosed metal cable trays, or underground may be installed without arc-fault protection. Detached structures whose only purpose is to house PV equipment are not considered buildings for this exception.

Rapid Shutdown of PV Systems on Buildings (NEC 690.12)

Rapid shutdown requirements are designed to safeguard firefighters and emergency personnel from lethal electrical shock when operating on roofs or within structures equipped with PV arrays. Controlled conductors must be brought to safe voltage thresholds within a tightly defined window following shutdown initiation.

                    ┌────────────────────────────────────────────────────────┐
                    │             NEC 690.12 RAPID SHUTDOWN BOUNDARIES       │
                    └───────────────────────────┬────────────────────────────┘
                                                │
             ┌──────────────────────────────────┴──────────────────────────────────┐
             ▼                                                                     ▼
┌────────────────────────────────────────┐             ┌────────────────────────────────────────┐
│         OUTSIDE ARRAY BOUNDARY         │             │         INSIDE ARRAY BOUNDARY          │
├────────────────────────────────────────┤             ├────────────────────────────────────────┤
│ - More than 1 ft (300 mm) from array   │             │ - Within 1 ft (300 mm) of array        │
│ - Includes wiring inside the building  │             │ - Enclosed beneath array surface       │
│ - Limit: ≤ 30 Volts within 30 seconds  │             │ - Option: ≤ 80 Volts within 30 seconds │
│ - Measured between conductors & ground │             │ - Or listed PV hazard control system   │
└────────────────────────────────────────┘             └────────────────────────────────────────┘

Spatial Boundaries

1. Inside the Array Boundary: Defined as the perimeter extending 1 foot (300 mm) from the solar module array in all directions, as well as the area beneath the array surface.
2. Outside the Array Boundary: Any point more than 1 foot (300 mm) from the array, including PV conductors run down the building and through its interior to the inverter or disconnect.

Controlled Conductor Voltage Limits

• Outside Boundary Conductors: Controlled conductors located outside the boundary must be reduced to 30 volts or less within 30 seconds of rapid shutdown initiation, measured between any two conductors and between any conductor and ground. (The 240-volt-ampere limit some older study materials mention dates from the 2014 NEC and no longer applies.)
• Inside Boundary Conductors: NEC 690.12(B)(2) gives three ways to comply: a listed PV hazard control system; reducing controlled conductors to 80 volts or less within 30 seconds; or a PV array with no exposed wiring methods or conductive parts, installed more than 8 feet from exposed grounded conductive parts. Most installers meet this with module-level power electronics (MLPE), such as microinverters or dc optimizers with built-in shutdown.

Initiation and Labeling

• Initiation Devices (690.12(C)): The initiation device is the service disconnecting means, the PV system disconnecting means, or a readily accessible switch that plainly shows whether it is "off" or "on". For one- and two-family dwellings, an initiation device must be at a readily accessible location outside the building.
• Building Label (690.56(C)): A permanent label at each service equipment location the PV system connects to (or another approved, readily visible location) shows where the rapid shutdown initiation devices are. It includes a simple diagram of a building with a roof and begins "SOLAR PV SYSTEM IS EQUIPPED WITH RAPID SHUTDOWN", with the title in capital letters at least 3/8 inch high, black on a yellow background.
• Switch Label (690.56(C)(2)): A rapid shutdown switch has a reflective label on it or within 3 feet of it reading "RAPID SHUTDOWN SWITCH FOR SOLAR PV SYSTEM", in white capital letters at least 3/8 inch high on a red background.

PV System Disconnecting Means (NEC 690.13)

Every PV system must have a means to disconnect it from all wiring systems, including power systems, energy storage systems, and utilization equipment:

• Location (690.13(A)): The PV system disconnecting means must be installed at a readily accessible location.
• Simultaneous Disconnection (690.13(E)): It must simultaneously disconnect the PV system conductors that are not solidly grounded from all conductors of other wiring systems. On many modern systems it is an ac disconnect at the inverter output.
• Number of Disconnects (690.13(C)): Each PV system disconnecting means may consist of not more than six switches or circuit breakers in a single enclosure or group of separate enclosures.
• Marking (690.13(B)): It must plainly indicate whether it is open (off) or closed (on) and be permanently marked "PV SYSTEM DISCONNECT" or equivalent. Where the line and load terminals can be energized in the open position, it also needs a warning label about the shock hazard on both sides.
• Ratings (690.13(E)): It must have ratings sufficient for the maximum circuit current, available fault current, and voltage at its terminals.

Grounding and Bonding of PV Arrays (NEC 690.43 & 690.47)

• Equipment Grounding Conductors (EGC): Metal module frames, conduit raceways, junction boxes, and inverter enclosures must be bonded together and connected to an EGC sized per NEC 250.122 based on the overcurrent protective device rating.
• Module Bonding: Anodized aluminum module frames require listed bonding devices (such as stainless-steel star washers, bonding clips, or WEEB devices) that pierce the nonconductive oxide coating to ensure metallic continuity.
• Auxiliary Grounding Electrodes: An auxiliary grounding electrode (such as a ground rod mounted near a roof-mounted or ground-mounted array) is permitted by NEC 250.54 and 690.47. If installed, it must be connected to the equipment grounding conductor, but it is not required to satisfy the 25-ohm resistance requirement.

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2. Energy Storage Systems: NEC Article 706

Article 706 applies to all energy storage systems (ESS) with a capacity greater than 3.6 MJ (1 kWh), whether stand-alone or interactive with other power sources. Examples include lithium-ion battery cabinets, flow batteries, and flywheel systems. ESS units store energy from renewable sources or the utility grid to provide load leveling, peak shaving, or backup standby power.

ESS Disconnecting Means (NEC 706.15)

A means must be provided to disconnect the ESS from all wiring systems, including other power systems, utilization equipment, and its premises wiring (706.15(A)):

• Location (706.15(B)): The disconnect must be readily accessible and must be located within the ESS, or within sight of and within 10 feet of the ESS. If it is not within sight of the ESS, the disconnect (or the enclosure that gives access to it) must be lockable in accordance with 110.25.
• Within-Sight Definition: Under NEC Article 100, "within sight" means visible and not more than 50 feet (15 m) away.
• Lockability: NEC 110.25 requires the locking provision to stay in place whether or not the lock is installed.
• Marking: The disconnect must plainly show whether it is open or closed and carry the labels Article 706 requires, including the nominal ESS voltage and available fault current.

Working Space and Ventilation

• Working Clearances: ESS equipment must comply with NEC 110.26 working space requirements (minimum 3 feet front depth clearance for 0–150V to ground, 30 inches width, and 6.5 feet headroom).
• Ventilation: Vented lead-acid batteries release hydrogen while charging. NEC 480.10(A) requires enough diffusion and ventilation to prevent an explosive mixture, and the fire codes typically limit hydrogen to 1% of the room volume.

ESS Emergency Shutdown (NEC 706.15)

One-family and two-family dwellings with an ESS must include an emergency shutdown function:

• The means to initiate ESS shutdown must be at a readily accessible location outside the building, where firefighters can reach it.
• Where the ESS works with a PV system, check the equipment listings and labels so responders can find both the PV rapid shutdown initiation device and the ESS shutdown.

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3. Electric Vehicle Power Transfer Systems: NEC Article 625

Article 625 governs the electrical conductors and equipment external to an electric vehicle that connect the vehicle to an electric supply. Electric Vehicle Supply Equipment (EVSE) ranges from portable 120V Level 1 cords to hardwired 208V/240V Level 2 chargers and high-voltage commercial DC fast chargers (DCFC).

Branch Circuit Sizing & Overcurrent Protection (NEC 625.41 & 625.42)

The key sizing rule for EV charging is the continuous load designation:

NEC 625.42 (summary): Power transfer equipment must have a rating sufficient for the load served, and electric vehicle charging loads are considered continuous loads for the purposes of Article 625.

NEC 625.41 (summary): Overcurrent protection for feeders and branch circuits supplying the equipment must be sized for continuous duty, with a rating of not less than 125% of the equipment's maximum load.

Under NEC 210.19(A) and 210.20(A), conductors and overcurrent protective devices supplying continuous loads must be sized at not less than 125% of the continuous load current.

$\text{Minimum OCPD Rating} = \text{EVSE Continuous Current Rating} \times 1.25$

Conductor Temperature Sizing Note: Although THHN has a $90^\circ\text{C}$ rating under Table 310.16, NEC 110.14(C)(1)(a) limits circuits rated 100 A or less to the $60^\circ\text{C}$ column unless the equipment terminals are listed and identified for $75^\circ\text{C}$. The table assumes $75^\circ\text{C}$ terminals at both ends, which is typical of modern breakers and EVSE. For example, 8 AWG copper (50 A at $75^\circ\text{C}$) can serve a 40-A charger on a 50-A breaker; with $60^\circ\text{C}$ terminals, it would need 6 AWG (55 A). For a 48-A charger on a 60-A breaker, 6 AWG copper rated 65 A at $75^\circ\text{C}$ is compliant.

EVSE Disconnecting Means (NEC 625.43)

Not every EV charger needs its own disconnect under Article 625. NEC 625.43 sets the threshold:

• Threshold Requirement: For equipment rated more than 60 amperes OR more than 150 volts to ground, a disconnecting means must be provided.
• Location: The disconnect must be installed in a readily accessible location. Article 625 does not require it to be within sight; if it is remote from the EVSE, a plaque on the equipment must show where it is.
• Lockability: The disconnecting means must be lockable open in accordance with NEC 110.25.

Field Interpretation: A typical residential 40-A or 48-A, 240-V Level 2 EVSE has 120 volts to ground ($\le 150\text{V}$) and is rated $\le 60\text{A}$, so 625.43 does not require a separate disconnect (other rules, such as 422.31 for cord-connected equipment, can still apply). An 80-A, 240-V Level 2 EVSE or a 480-V three-phase DC fast charger exceeds the threshold, so it needs a readily accessible, lockable disconnect, with a location plaque if the disconnect is remote.

Indoor Charging Ventilation Requirements (NEC 625.52)

• Non-Ventilated Equipment: Modern commercial and residential EVSE marked "Ventilation Not Required" utilizes sealed battery management systems that do not off-gas during normal charging. No mechanical ventilation is required.
• Ventilated Equipment: Where EVSE requires ventilation during charging, mechanical ventilation must be provided at the rate given by the tables in NEC 625.52(B), which base the airflow on the supply voltage and current of the charging equipment. The ventilation system must be electrically interlocked with the EVSE so that charging cannot initiate unless the exhaust fan is operating.

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4. Master Comparison: Solar PV, ESS, and EV Charging