Nirav Dhanani An AC disconnect is a switch that isolates a solar inverter's AC output from the building service and the utility grid. NEC 2023 Article 705 sets disconnecting-means rules for interconnected sources, and many utilities also require a lockable, visible-blade switch near the meter so line workers can confirm the PV system is isolated.
Quick Facts
| Field | Detail |
|---|---|
| Term | AC Disconnect |
| Category | Solar Components |
| Standards | NEC 690.15, NEC 705.20, UL 98 |
| Typical Rating | 30-200 A, 240-480 V |
| Difficulty Level | Beginner |
NEC 690.15 Requirements
- Disconnect between inverter and utility service.
- Lockable open with provision for lockout/tagout.
- Visible-blade or visible-open indicator.
- Within 10 ft of the meter (utility-specific).
- Labeled per NEC 690.13(B): “AC DISCONNECT FOR PV SYSTEM.”
Types
- Square D heavy-duty safety switch (residential dominant).
- Eaton DG-series (residential alternative).
- Bussmann fused/non-fused safety switches.
- Inverter-integrated AC breakers (some utilities accept).
Architecture changes the count and location, not the requirement. A string or central inverter feeds one AC disconnect ahead of the service; a microinverter fleet still needs a single disconnect ahead of the combined trunk feeder, since utility line workers isolate the whole PV output, not each micro-unit individually.
Sizing Example
8 kW residential inverter, 240 V output:
- Continuous output current: 8000 / 240 = 33.3 A.
- Sizing: 1.25 × 33.3 = 41.7 A → 60 A standard rating.
- 60 A, 240 V AC disconnect (e.g., Square D DU222RB).
Best Practices
- Specify outdoor-rated (NEMA 3R minimum) for outdoor installations.
- Locate near the meter for utility personnel access.
- Use load-break-rated devices.
- Maintain clear unobstructed access (NEC 110.26 working clearance).
- Label clearly per NEC 690.13(B) and utility tariff.
- Show the disconnect at its correct position on the project’s single-line diagram, reviewers cross-check the physical label against the SLD symbol during plan check.
Standards & Certifications
- NEC 690.15, 705.20.
- UL 98, Disconnect switches.
- UL 489, Circuit breakers.
Key Takeaways
- AC disconnect required by NEC 690.15 between solar inverter and utility service.
- Must be lockable open with visible-open indicator.
- Sized to 1.25 × continuous AC output; voltage rating to system voltage.
- Most utilities require an exterior AC disconnect near the meter for line-worker safety.
- Label per NEC 690.13(B) and any utility-specific tariff requirements.
Related Reading
An AC disconnect only satisfies plan check if it shows up correctly on paper as well as in the field, the disconnect symbol, its label text, and its physical location all have to match across the electrical drawing set. Our guide to solar SLD software covers how NEC-compliant single-line diagrams get built and auto-checked for exactly this kind of interconnection equipment.
Projects that need the disconnect coordinated across the full electrical package, SLD, panel schedules, and utility interconnection paperwork, are the ones our Electrical CEIG Drawings service is built around. For the DC-side equivalent of this isolation requirement, see DC Disconnect; together, the two devices are what most AHJs and utilities check first during a service-panel walk-down.
Frequently Asked Questions
3 commonly searched questions about AC Disconnect.
Where is the solar AC disconnect located?
Can the main breaker act as the solar AC disconnect?
Do microinverter systems need an AC disconnect?
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