UL 3700 Explained: The Safety Standard for Plug-In Solar

For years, the main safety objection to plug-in solar in the US was simple: there was no standard for it. Inverters could be listed under UL 1741, which covers grid-connected inverters, but nothing addressed a consumer plugging a generator into a household outlet. UL 3700 fills that gap, and it is one reason legislators became comfortable passing plug-in laws in 2026.

What UL 3700 tests

UL 3700 looks at the plug-in solar product as a system. The main concerns are:

• The live-pin problem. If you unplug a solar device while it is producing, the prongs of the plug must not carry voltage. A certified device detects the loss of grid connection and shuts off almost instantly.
• Anti-islanding. The inverter must stop producing when the grid goes down, so it cannot energize lines that workers believe are dead.
• Circuit overload. Output limits and labeling help prevent a situation where solar input plus a heavy appliance push more current through the wiring than the breaker sees.
• Construction and marking. Cord quality, weather resistance and clear instructions for the user.

UL 3700 vs UL 1741

A kit using a UL 1741-listed microinverter is not automatically UL 3700 certified. In states that simply require a listing by a nationally recognized lab, a UL 1741 inverter may be acceptable. In states that name UL 3700, it is not enough.

Which products are certified?

Certification takes time and money, so the list is short. Reports in 2026 identified the Hoymiles HiFlow microinverter used in Bright Saver’s kits as the first microinverter to achieve UL 3700, and APsystems’ EZ1-LV microinverter as certified in July 2026. Several other kits, including Craftstrom’s and EcoFlow’s STREAM products, were reported as in progress. Our list of UL 3700 certified kits is updated as that changes.

How to verify a claim

1. Look for the certifying lab’s mark on the product label, not just on the website.
2. Note the file number and look it up in the lab’s public database (UL Product iQ for UL listings).
3. Check whether the certificate covers the system or only a component.
4. Be wary of phrases like “designed to meet” or “compliant with” without a certificate. They are not the same as certified.

Is a non-certified kit dangerous?

Not necessarily. Millions of European balcony systems run on microinverters certified to European standards such as VDE-AR-N 4105, and fires attributable to them are rare. But in US states that require certification, an uncertified device does not qualify for the legal protections, and your insurer may take a dim view after an incident. Read is plug-in solar safe? for the risks that actually matter.

What about the UK and Europe?

The UK uses its own Interim Product Specification for plug-in solar (see UK rules). Germany relies on its grid code and a product standard for plug-in solar devices that has been in development alongside the country’s 800 W rules. A UL 3700 certificate does not automatically qualify a product in those markets, and vice versa.

Why certification took so long

Standards bodies had to answer questions that do not arise with professionally installed solar: what if a consumer unplugs the device mid-production, plugs two devices into the same circuit, or uses an old outlet? UL 3700 addresses these at the product level, while state laws limit total output. Laboratories then needed time to test products, and manufacturers had to redesign some to pass. The first certifications arriving in mid-2026 is a normal pace for a new standard.

Frequently asked questions