16.1 Solar PV Systems (Article 690)
Key Takeaways
- PV source-circuit maximum current = Isc × 1.25 per 690.8(A)(1)(a); conductors sized at 125% of that value per 690.8(B), yielding Isc × 1.5625 for source-circuit conductors.
- PV maximum system voltage = sum of series-connected module Voc × the Table 690.7(A) low-temperature correction factor per 690.7(A).
- PV OCPD must be rated at least 125% of the 690.8(A) maximum current per 690.9.
- Single-conductor PV source circuits within the array may use USE-2 or PV Wire per 690.31(C)(1); conductors leaving the array boundary must enter a raceway.
- Rapid shutdown per 690.12 limits controlled conductors inside the array boundary to 80 V within 30 seconds; outside the array boundary, controlled conductors are limited to 1 ft of the array or 3 ft from the point of entry into a building.
Why Article 690 Matters for the TX Journeyman Exam
Renewable Energy Technologies is content-outline area 10, and Article 690 (Solar Photovoltaic (PV) Systems) is the largest piece of that area. The exam tests PV in both parts:
- NEC Knowledge part: wiring methods (690.31), rapid shutdown (690.12), disconnecting means (690.13/690.15), and required labeling (690.53).
- Calculations part: cold-weather maximum system voltage (690.7(A)) and continuous-current conductor/OCPD sizing (690.8/690.9).
PV calculations trip up many candidates because the NEC stacks two 1.25 factors — one for the PV source-circuit maximum current and one for continuous operation — before you even touch a table. Master the multiplier chain and you will answer most PV calculation questions correctly.
PV Maximum System Voltage — 690.7(A)
A PV module's open-circuit voltage (Voc) rises as temperature drops. The NEC requires you to calculate the maximum system voltage using the lowest expected ambient temperature at the installation site.
The Rule
Per 690.7(A), for crystalline and multicrystalline silicon modules, the maximum DC voltage equals the sum of the series-connected module Voc values multiplied by the Table 690.7(A) low-temperature correction factor.
Table 690.7(A) — Selected Correction Factors
| Lowest Expected Ambient Temp | Correction Factor |
|---|---|
| +5°C | 1.06 |
| 0°C | 1.09 |
| -10°C | 1.17 |
| -20°C | 1.25 |
| -40°C | 1.50 |
Exam tip: If the manufacturer provides a voltage-temperature coefficient, you may use that instead per 690.7(A)(1). For systems ≥100 kW, a PE-stamped engineered method is allowed per 690.7(A)(3). For most journeyman questions, use the table.
Worked Example — Cold-Weather Max Voltage
Given: A PV source circuit has 10 modules in series. Each module has Voc = 39.8 V. The lowest expected ambient temperature is -10°C.
Formula: Max system voltage = (number of modules in series × Voc per module) × Table 690.7(A) factor
Substitution: (10 × 39.8 V) × 1.17
Result: 398 V × 1.17 = 465.7 V
This value must not exceed the maximum DC voltage rating of the inverter, conductors, and other connected equipment.
PV Circuit Currents — 690.8(A)
PV current also must be corrected for the fact that sunlight can exceed standard test conditions. The NEC defines maximum current for each PV circuit type.
Key Formula — 690.8(A)(1)(a) Source Circuits
PV source-circuit maximum current = Isc × 1.25
where Isc is the short-circuit current of the module (or parallel combination of module strings).
| Circuit Type | 690.8(A) Formula |
|---|---|
| PV source circuit (module string) | Isc × 1.25 |
| PV output circuit (after combiner) | Isc × 1.25 |
| Inverter output circuit (AC) | Inverter continuous output current rating |
Conductor and OCPD Sizing — 690.8(B) and 690.9
This is where the second 1.25 factor enters. PV circuits are considered continuous loads.
Conductor Sizing — 690.8(B)
PV circuit conductors must have an ampacity not less than 125% of the 690.8(A) maximum current.
Net multiplier for a PV source-circuit conductor: Isc × 1.25 × 1.25 = Isc × 1.5625
OCPD Sizing — 690.9
PV OCPDs must be rated at not less than 125% of the 690.8(A) maximum current.
Net multiplier for PV OCPD: Isc × 1.25 × 1.25 = Isc × 1.5625
Worked Example — Size the Source-Circuit Conductor and OCPD
Given: A PV source circuit has Isc = 9.5 A. The conductors are copper, terminations rated 75°C, no more than 3 current-carrying conductors in the raceway, ambient 30°C.
Step 1 — Maximum current (690.8(A)): 9.5 A × 1.25 = 11.875 A
Step 2 — Conductor ampacity (690.8(B)): 11.875 A × 1.25 = 14.84 A
From Table 310.16, 75°C column, copper: 14 AWG = 20 A. That satisfies 14.84 A.
Step 3 — OCPD rating (690.9): 11.875 A × 1.25 = 14.84 A
Per 240.6(A), the next standard rating at or above 14.84 A is 15 A.
Trap: Candidates often apply only one 1.25 factor. The NEC stacks them: 690.8(A) gives you the maximum current, then 690.8(B) or 690.9 adds the continuous 125% on top. Two multipliers, not one.
Wiring Methods — 690.31(C)(1)
Single-conductor cables for PV source circuits (the DC wiring within the array) have a special allowance.
Per 690.31(C)(1), single-conductor cables in exposed outdoor locations within the PV array may be:
- PV Wire or PV cable, or
- Single-conductor cable marked sunlight resistant, Type USE-2, and Type RHW-2
| Requirement | Detail |
|---|---|
| Support spacing (≤ 8 AWG) | Every 24 in (600 mm) |
| Support spacing (> 8 AWG) | Every 54 in (1400 mm) |
| Array boundary rule | Single-conductor USE-2/PV Wire permitted only within the array; once conductors leave the array boundary, they must be in a raceway or appropriate wiring method |
This array-boundary restriction is a common exam question. If the question says the conductors run from the array to a combiner box 30 ft away in exposed outdoor location, the answer is a raceway — not single-conductor USE-2.
Rapid Shutdown — 690.12
Rapid shutdown reduces energized conductor voltage for firefighter safety. The 2023 NEC rules depend on where the conductors are relative to the array boundary.
| Location | Rapid Shutdown Requirement |
|---|---|
| Inside the array boundary | Controlled conductors must be reduced to ≤ 80 V within 30 seconds of rapid-shutdown initiation |
| Outside the array boundary | Controlled conductors must be limited to 1 ft of the array origin or 3 ft from the point of entry into a building, and to ≤ 80 V within 30 seconds |
The array boundary is the smallest convex polygon enclosing all PV modules and wiring. A rapid-shutdown initiation device must be installed at a readily accessible location outside the building.
Disconnecting Means — 690.13 and 690.15
690.13 requires a means to disconnect the PV system from all wiring systems, including the inverter, utilization equipment, and premises wiring. The disconnect must:
- Be readily accessible
- Plainly indicate open/closed position
- Be capable of being locked in the open position if not within sight (per 110.25)
690.15 permits disconnecting means for each PV circuit (e.g., at a combiner box) so individual strings can be isolated for maintenance.
Required Labeling — 690.53
The DC disconnect nameplate or permanent plaque must list the following per 690.53:
| Required Label Item | Example Value |
|---|---|
| Maximum current | 11.9 A |
| Maximum system voltage | 466 V |
| Short-circuit current (Isc) | 9.5 A |
| Open-circuit voltage (Voc) | 39.8 V |
| Operating current | 8.2 A |
| Operating voltage | 320 V |
Exam note: 690.53 labeling is a classic Knowledge-part question. Memorize the six required items: max current, max voltage, Isc, Voc, operating current, operating voltage.
A PV source circuit has Isc = 8.0 A. What is the minimum conductor ampacity required by 690.8(A) and 690.8(B) combined?
A PV array has 12 modules in series, each with Voc = 40 V. The lowest expected ambient temperature is -20°C. Using Table 690.7(A), what is the maximum system voltage?
Which wiring method is permitted for single-conductor PV source circuits in exposed outdoor locations WITHIN the PV array boundary per 690.31(C)(1)?
Per 690.12, conductors inside the PV array boundary must be reduced to what voltage within how many seconds of rapid-shutdown initiation?