Building Codes for Off-Grid Solar: NEC 690 & What Applies
- NEC Article 690 is the primary national standard governing solar PV installations in the US.
- NFPA 855 governs battery energy storage systems — increasingly relevant as LiFePO4 banks grow larger.
- Off-grid systems face fewer code requirements than grid-tied since they don't connect to utility infrastructure.
- Following NEC 690 is good practice even without a permit — it represents minimum safe installation standards.
- Local amendments can be stricter than the base NEC — always check with your local authority.
The main codes that apply
| Code | What it covers | Applies to off-grid? |
|---|---|---|
| NEC Article 690 | Solar PV systems — wiring, disconnects, grounding, labelling | Yes |
| NEC Article 705 | Interconnected power sources (grid connection) | No — grid-tied only |
| NEC Article 480 | Battery storage systems | Yes — for battery banks |
| NFPA 855 | Energy storage systems safety standard | Yes — for larger battery systems |
| IBC / IRC | Building codes — structural (roof loading, ground mounts) | Yes — for permanent structures |
| Local amendments | State and county modifications to base codes | Varies |
NEC Article 690 — key requirements
Article 690 is the foundation of solar electrical safety in the US. Even if your jurisdiction doesn't require permits, following 690 protects you and your property. Key requirements:
690.12 — Rapid shutdown
Grid-tied systems in most jurisdictions require rapid shutdown capability — a means to de-energise roof conductors within 30 seconds for firefighter safety. Off-grid systems are generally exempt from rapid shutdown requirements since they don't connect to the utility and aren't energised from the grid side during a fire response. Check your local AHJ (Authority Having Jurisdiction) for their interpretation.
690.13 — Disconnecting means
A readily accessible DC disconnect must be provided for the solar array. This allows the system to be safely de-energised for maintenance or emergencies. For off-grid systems: a disconnect between the panel array and charge controller meets this requirement. Location must be accessible without entering a confined space.
690.31 — Wiring methods
- Outdoor conductors must be listed for outdoor use — PV wire (USE-2) or in weatherproof conduit
- Conductors must be protected from physical damage
- MC4 connectors must be listed and used with compatible connectors of the same brand
- Conductors in conduit must not exceed conduit fill limits
690.41 — System grounding
The metal frames of all solar panels, mounting rails and equipment enclosures must be bonded together and connected to a grounding electrode system. This protects against lightning and ensures fault currents trip overcurrent protection rather than flowing through people or causing fires.
690.35 — Ungrounded systems
Modern MPPT charge controllers typically operate as ungrounded (floating) systems — neither the positive nor negative conductor is connected to ground. This is permitted under NEC 690.35 with appropriate ground fault protection. Most quality controllers include internal GFPD.
690.64 — Overcurrent protection
All conductors must be protected by overcurrent devices (fuses or breakers) sized appropriately for the conductor ampacity. The 18-inch rule (fuse within 18 inches of battery positive terminal) comes from this section. See our fuse placement guide.
690.52 — Labelling requirements
NEC requires specific labels on solar installations:
- All combiner boxes, disconnects and charge controllers must be labelled with operating voltage and current
- "Caution: Solar Electric System" labels on conduit
- DC disconnect must be labelled as such
- Batteries must be labelled with voltage and capacity
NFPA 855 — battery storage safety
NFPA 855 (Standard for the Installation of Stationary Energy Storage Systems) has become increasingly relevant as off-grid battery banks grow larger. Key provisions:
| Battery size | NFPA 855 requirements |
|---|---|
| Under 20 kWh (residential) | Minimal — basic installation requirements |
| 20–80 kWh | Separation distances, ventilation, fire detection |
| Over 80 kWh | Sprinkler systems, fire-rated enclosures, utility notification |
Most residential off-grid systems are well under 20 kWh — the typical cabin has 5–15 kWh and the typical home system 15–30 kWh. Systems in this range face minimal NFPA 855 requirements.
What inspectors actually check
If your installation is inspected, inspectors typically focus on:
- Overcurrent protection: Is every conductor protected? Are fuses within 18 inches of the battery?
- Disconnect accessibility: Can the system be safely de-energised from an accessible location?
- Grounding: Are all metal components bonded? Is there a grounding electrode?
- Wire sizing: Are conductors appropriately sized for the current they carry?
- Conduit and weatherproofing: Are outdoor conductors protected from UV and physical damage?
- Labelling: Are required warning labels present?
Frequently asked questions
Does NEC 690 apply if I don't pull a permit?
NEC is adopted by reference into law in most US jurisdictions — which means it technically applies whether or not you pull a permit. More practically: following NEC regardless of permit status protects you legally, reduces fire risk and makes any future inspection straightforward.
Do I need a licensed electrician to meet NEC 690?
NEC doesn't specify who must do the work — that's determined by local licensing requirements. Many jurisdictions allow homeowners to do their own electrical work on their primary residence under an owner-builder exemption. The quality and safety of the work is what NEC governs, not who performs it.
My county doesn't adopt NEC — do these requirements still apply?
All 50 states have adopted some version of the NEC. A small number of rural counties may not enforce it actively, but the code still represents the legal minimum standard. In practice, following NEC even in low-enforcement areas is simply the right approach for a safe installation.