What Is UL 3700?

UL 3700 is the safety standard published by Underwriters Laboratories (UL) for plug-in grid-interactive power conversion equipment. In plain language, it is the safety certification for devices that plug into a wall outlet and feed power back into your home's electrical circuits.

This standard is referenced in every major piece of plug-in solar legislation in the US. Utah's HB 340 requires it. Colorado's HB 26-1007 requires it. California's SB 868 would require it. Understanding UL 3700 is essential for anyone involved in plug-in solar — consumers, electricians, property managers, and policymakers.

What UL 3700 Covers

Anti-Islanding Protection

The most critical safety feature. Anti-islanding ensures that when the grid goes down (a power outage), the plug-in solar system automatically disconnects within 2 seconds. This prevents the system from backfeeding power into de-energized utility lines, which could endanger utility workers performing repairs.

This is the same protection required in traditional grid-tied rooftop solar inverters (IEEE 1547). UL 3700 extends this requirement to plug-in devices.

Ground Fault Protection

UL 3700 requires systems to detect ground faults — unintended current paths through the grounding system — and disconnect automatically. This protects against electrical shock hazards.

Overcurrent Protection

The standard limits the amount of current a plug-in system can feed back into a circuit. Typically, this is capped at 15A on a standard 20A household circuit, ensuring the circuit is not overloaded. This is consistent with NEC 2023 Article 625 requirements.

Power Quality

UL 3700 sets limits on Total Harmonic Distortion (THD), voltage regulation, and frequency stability. The power output must be clean enough to not interfere with other devices on the same circuit or cause issues for the utility grid.

Why It Matters for Legislation

UL 3700 gives legislators and regulators a clear, objective safety benchmark. Instead of writing complex technical requirements into law, they can simply require UL 3700 certification. This simplifies legislation, reduces ambiguity, and ensures a consistent safety standard across all states.

Which Systems Have UL 3700?

As of 2026, several plug-in solar systems have obtained UL 3700 certification. When evaluating a system, verify the UL 3700 certification directly on the product documentation or the UL Product iQ database. Systems without UL 3700 may not comply with state legislation.

For more on how plug-in solar systems work and how they compare to other solar technologies, visit our How It Works page.