Over/Under Voltage Protection Relay
Egypt's power grid is prone to voltage fluctuations — especially in summer when power cuts and sudden returns send surges through the lines. These fluctuations damage refrigerators, air conditioners, and washing machines in seconds. An over/under voltage protection relay disconnects your home the moment voltage leaves the safe range, then automatically reconnects once the grid stabilises.
By the Ases Kahraba team — Last updated: March 2026
Quick Answer
Complete guide to over/under voltage protection relay — how it works, correct settings for Egypt, difference between relay and stabilizer, and prices in the Egyptian market.
How the Protection Relay Works & What to Choose
- Principle: the device continuously monitors incoming voltage. If it rises above 250V or drops below 170V (common Egyptian setting), it signals a contactor to disconnect the circuit entirely. After a programmed delay (3–5 minutes) it automatically reconnects.
- Types: single-phase for apartments and shops — three-phase for villas and industrial premises. Digital display models show live voltage; analog models are cheaper.
- Brands available in Egypt: Finder (Italian, most reliable) — Gewiss — Doepke — Elko EP. Chinese-branded units sell for EGP 80–150 but have less stable calibration. Always read the datasheet before buying.
- Correct settings for Egypt: Under-voltage cutoff: 170–180V — Over-voltage cutoff: 240–250V — Reconnect delay: at least 3 minutes to allow the grid to stabilise after power returns.
- vs. Voltage Stabilizer: a stabilizer corrects voltage and outputs a steady 220V as long as fluctuation is within its correction range. The relay only cuts power — it doesn't correct. Relays are cheaper and faster to trip; stabilizers maintain operational continuity.
- Installation: fits inside the main distribution panel alongside a contactor (50A or larger depending on load). Wiring: relay input on A1/A2 coil control, output drives the contactor coil. A qualified electrician needs about one hour.
- Prices in Egypt (2026): digital single-phase relay (Finder/Gewiss): EGP 400–700 — 32A contactor: EGP 200–400 — installation: EGP 300–600. Total: EGP 900–1,700 — far less than a damaged fridge or AC unit.
Frequently Asked Questions
Does an over/under voltage relay protect against lightning?
No. Lightning produces an extremely fast, high-energy spike (microseconds) that a standard relay cannot disconnect in time. For lightning protection you need a dedicated SPD (Surge Protective Device). The relay protects against normal grid fluctuations only.
Do I need one relay for the whole apartment or one per appliance?
One central relay in the main panel protects the entire apartment — the most economical solution. Individual plug-in protection units suit adding protection to a single appliance (e.g. a fridge or AC) where a sub-panel isn't practical.
What is normal voltage in Egypt and how do I know if it's low?
Egypt's nominal single-phase voltage is 220V; three-phase is 380V. In summer peak hours it can drop to 170–190V. Measure with a cheap digital voltmeter (EGP 50–100). Low voltage also shows as dim lighting and abnormal motor sounds.
What happens to a fridge or AC during overvoltage?
Overvoltage increases motor current, burning windings or damaging the compressor. Damage occurs in seconds during a sudden surge (power returning after an outage). AC compressor repair costs EGP 1,500–4,000 — more than a EGP 1,000 protection relay.
Can I adjust the relay myself or do I need an electrician?
Adjusting the relay thresholds and delay time is relatively straightforward and explained in the manual. However, panel installation requires a qualified electrician — wiring errors can destroy the device or cause a fire. Ask the electrician to test it by simulating undervoltage after installation.
What does voltage protection relay installation cost in Egypt?
Total cost EGP 900–1,700 (relay + contactor + labour). Contact Ases Kahraba for an inspection and guaranteed installation.