The problem: bad grid voltage
A lost neutral in the street or in an old apartment riser can push up to 380 V into a 230 V home for seconds or minutes. Compressors, boilers and electronics burn out — a classic and expensive failure in older grids.
What a voltage relay does
A voltage relay measures the mains voltage and disconnects the whole panel when it leaves a safe window (for example 170–250 V), then reconnects automatically after a delay once the grid is healthy again.
Recommendation
- CIS profile: strongly recommended — the rule engine insists on it.
- EU profile: optional but cheap insurance, especially in buildings with aging infrastructure.
One or three relays are used depending on the number of phases.