UL 943
The standard for ground-fault circuit interrupters — the protection that shuts a circuit off to stop you being electrocuted.
What UL 943 covers
Ground-fault circuit interrupter performance: how quickly and reliably a device trips on a ground fault. It's the protection standard for the GFCI outlets and breakers already in your home.
Why it matters for balcony solar
One of the specific hazards plug-in solar creates: current back-fed into a circuit can blind or interfere with the ground-fault protection already there — the part that protects you. UL 3700 pulls UL 943 into its reference chain for exactly this reason.
The common mix-up
GFCI feels unrelated to solar, but back-feeding a circuit is precisely what can defeat it. That interaction is one of the four hazards UL 3700 was written to handle.
UL 943 is one of several UL standards behind a plug-in system. See how they fit together →
What to look for when buying
You don't buy this — it's already in your home. It's why plug-in solar needs testing that ordinary gear doesn't.