Short answer: Article 690 covers solar photovoltaic systems: array circuits, inverters, disconnects, rapid shutdown and grounding. Article 700 covers emergency systems that building codes require, such as egress lighting, which must get power back within the time Article 700 sets (10 seconds for most emergency loads) on wiring kept separate from normal wiring. In the standard PV source-circuit calculation the 125% factor is applied twice (once for maximum current, once for conductor sizing); PV voltage rises in cold weather.
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Tsai Electro is an independent learning site. Not affiliated with TDLR, PSI or NFPA. We explain the method in our own words and do not reproduce NEC text. Check every rule in your own 2026 NEC. PV arrays can produce hazardous DC voltage whenever light hits them, even with the inverter off or after rapid shutdown has been started; work on PV only under supervision and your employer’s safety program.
Where these systems sit in the NEC
Article 690 is in Chapter 6 and Article 700 is in Chapter 7. Both chapters add to or change the general rules in Chapters 1 to 4. Texas uses the 2026 NEC for installations and exams from September 1, 2026 (TDLR rule adoption notice, PSI Candidate Information Bulletin).
| Article | Covers | Apprentice takeaway |
|---|---|---|
| 690 | Solar PV systems | The PV-specific rules: circuit sizing, disconnects, rapid shutdown, grounding |
| 705 | Interconnected power sources | How PV and other sources connect to the utility or a panel |
| 706 | Energy storage systems | Batteries and their disconnects |
| 700 | Emergency systems | Required by code for life safety; fastest and strictest |
| 701 | Legally required standby | Required by code, but not for life safety directly |
| 702 | Optional standby | Chosen by the owner, such as a home generator |
Trace a PV system source to load
- Modules and array. Modules are wired in series into strings. Series adds voltage.
- DC circuits. Conductors from the array to the inverter. These carry current any time there is light.
- Rapid shutdown. On buildings, PV circuits must be able to drop to a lower voltage quickly for firefighters (690.12).
- PV system disconnect. A means to disconnect the PV system from other wiring, marked and readily accessible (690.13).
- Inverter. Changes DC to AC.
- AC output and interconnection. Connects to the service or a panel under Article 705.
The 2026 code added rules for flexible equipment grounding conductors in PV systems (690.43), according to the City of Denison’s 2026 change summary (Denison 2026 NEC summary).
Worked example 1: PV circuit current
A module has a short-circuit current (Isc) of 11.20 A. One string feeds the inverter input.
- Maximum circuit current: 125% of Isc. 11.20 × 1.25 = 14.00 A (690.8(A)).
- Minimum conductor ampacity before any correction: another 125%. 14.00 × 1.25 = 17.50 A (690.8(B)).
- Together that is 156.25% of Isc: 11.20 × 1.5625 = 17.50 A.
Check: 17.50 ÷ 1.25 = 14.00, and 14.00 ÷ 1.25 = 11.20. Both steps reverse correctly.
The first 125% accounts for sunlight stronger than the test condition. The second is the usual continuous-current margin. Then apply temperature correction for the location, like any other conductor. This is a teaching example: before choosing a real conductor, check the full 2026 rules, the equipment ratings and any exceptions, and do not treat 17.50 A as a finished conductor selection.
Worked example 2: cold-weather voltage
PV voltage goes up as the module gets colder. Module data: open-circuit voltage (Voc) 49.50 V at 25°C, temperature coefficient of Voc −0.27% per °C. Lowest expected temperature at the site: −6°C. The code allows the manufacturer’s coefficient method (690.7(A)).
- Temperature difference from 25°C: 25 − (−6) = 31°C.
- Voltage increase: 31 × 0.27% = 8.37%.
- Cold Voc per module: 49.50 × 1.0837 = 53.64 V (53.643 before rounding).
- For a one- or two-family dwelling, PV DC circuits are limited to 600 V (690.7).
- 12 modules: 12 × 53.643 = 643.7 V. Too high.
- 11 modules: 11 × 53.643 = 590.1 V. Within 600 V.
Check: 600 ÷ 53.643 = 11.19, so 11 is the most modules that fit under this voltage limit alone. Same answer.
This is why a string that works on a summer afternoon can be over its limit on a cold winter morning. The inverter’s own maximum input voltage also has to be checked.
Emergency, legally required and optional standby
| Feature | 700 Emergency | 701 Legally required standby | 702 Optional standby |
|---|---|---|---|
| Who requires it | Building or fire codes, for life safety | Codes, for loads like some ventilation or communications | The owner |
| Typical loads | Egress lighting, exit signs, fire alarm, fire pumps in some designs | Systems that help firefighting or prevent hazards | A home or business generator |
| Time to restore power | Within 10 seconds | Within 60 seconds | No code time limit |
| Wiring | Kept independent of other wiring, with listed exceptions | Can share raceways with general wiring | General wiring rules |
| Testing | Witness test at installation, then periodic tests with records | Witness and periodic tests | Per the owner |
Rules to look up in your own NEC: transfer equipment for emergency systems must be automatic and listed for emergency use (700.6), power must be back within 10 seconds (700.12), and emergency wiring is kept separate from other wiring (700.10(B)). In North Texas, the NCTCOG amendments noted in the Denison summary allow the commissioning witness test to be done in person, remotely or by documentation acceptable to the inspector. Ask which amendments your city has adopted.
What this means in Texas
Installing PV is electrical work in Texas, so it is generally done by or through a TDLR-licensed electrical contractor, with apprentices working under supervision. Some exemptions exist in Texas law; check TDLR before relying on one.
Check yourself
Our own practice questions. Answers below each.
- Isc = 9.80 A. Maximum circuit current and minimum ampacity? Answer: 9.80 × 1.25 = 12.25 A; 12.25 × 1.25 = 15.31 A (15.3125).
- Voc 40.00 V, coefficient −0.30% per °C, low of −10°C. Cold Voc? Answer: 25 − (−10) = 35; 35 × 0.30% = 10.5%; 40.00 × 1.105 = 44.20 V.
- Exit sign lighting is on which article? Answer: Article 700, emergency systems.
- A homeowner’s standby generator? Answer: Article 702, optional standby.
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The code book for solar and emergency systems
NFPA 70, National Electrical Code (NEC), 2026 Edition, softbound. Articles 690 and 700 are in it. Read each section in your own copy before you rely on it.
FAQ
What does NEC Article 690 cover?
Solar photovoltaic systems, including array and inverter circuits, circuit sizing, disconnecting means, rapid shutdown for PV on buildings, wiring methods, grounding and markings. Interconnection with other sources is in Article 705 and batteries are in Article 706.
Why is PV current multiplied by 125% twice?
The first 125% sets the maximum circuit current, because sunlight can be stronger than the module test condition. The second 125% is the continuous-current margin used in this simplified conductor-sizing example, giving 156.25% of short-circuit current before applicable corrections and other code requirements.
How fast must an emergency system restore power?
Within 10 seconds for emergency systems under Article 700. Legally required standby systems under Article 701 have 60 seconds. Optional standby under Article 702 has no code time limit.
What is the maximum PV voltage on a house?
For one- and two-family dwellings, PV system DC circuits are limited to 600 volts. Calculate the cold-weather voltage of the string, not the voltage at 25°C, to check it.
Sources checked October 2026
- TDLR rule adoption notice, 2026 NEC: https://www.tdlr.texas.gov/news/rulemaking/2026/09/01/commission-adopts-rules-12/
- PSI Candidate Information Bulletin for TDLR (updated 9/15/2026): https://test-takers.psiexams.com/api/content/bulletin/1682
- TDLR exam page: https://www.tdlr.texas.gov/electricians/elecexam.htm
- City of Denison, 2026 NEC significant changes: https://denisontx.gov/DocumentCenter/View/4131/2026-National-Electrical-Code-Significant-Changes
- NFPA 70 (NEC), 2026 edition, Articles 690, 700, 701, 702, 705 and 706, read in your own copy: https://www.nfpa.org/codes-and-standards/nfpa-70-standard-development/70
