Arc fault detection for PV strings — what the ratings mean
The Siemens 5SM6094-1 is a SENTRON arc fault detection unit (AFDD) designed specifically for photovoltaic DC circuits. It is rated 40 A at 1000 V DC, single-pole, and detects series arcs down to 2 A minimum — meaning it can identify a failing connection in a PV string before the fault current climbs high enough to cause a fire. That 2 A threshold is the key: below that, a series arc may not be reliably detected, so the unit is sized for strings where the normal operating current stays above 2 A. The 1-pole design and 1000 V DC rating match the voltage of a typical residential or small commercial PV string (up to about 20 panels in series). The 40 A continuous current covers most single-string combiner boxes.
IP20 / NEMA 1 protection means it is for indoor or enclosed use only; the enclosure must protect against dust and moisture. Halogen-free and silicon-free construction reduces toxic smoke in a fire and avoids silicone outgassing that can contaminate PV connectors. Mounts in any position, with a fastening method of DIN rail (REG) or wall mounting. The 48 mm installation depth fits standard 60 mm deep enclosures. The unit is not short-time delayed (instantaneous trip) — it responds to the arc fault signature without intentional delay.