A voltage protector disconnects the supply when it goes out of range; a stabiliser corrects the voltage so equipment keeps running. Protectors are cheaper and cover the whole property from the distribution board. Stabilisers cost more, are usually sized per appliance, and are the right choice only where an interruption is unacceptable.
The core difference in one line
Protector: stop before damage occurs. Stabiliser: keep running through the problem.
That distinction decides which you need. If a fridge switching off for ten minutes is an inconvenience, a protector is sufficient. If a till, a server or a medical device stopping means real loss, correction is worth paying for.
Side by side
Voltage protector
- Fits on DIN rail at the board; one unit covers everything downstream.
- Adjustable upper and lower thresholds, with a reconnection delay.
- Low cost relative to what it protects.
- Does not correct voltage — the supply is simply cut until it recovers.
Stabiliser (AVR)
- Actively raises or lowers output toward nominal.
- Equipment continues operating through a sag.
- More expensive, physically larger, and usually rated per appliance rather than whole-property.
- Has limits — beyond its correction range it cannot help.
What most Egyptian properties actually need
For a home, a protector at the board is the highest-value purchase. It covers every circuit, costs a fraction of one replaced air-conditioner compressor, and addresses the dominant failure mode — sustained under-voltage.
For a shop or small business, the usual answer is both: a protector at the board for whole-property safety, and a stabiliser on the specific equipment that must not stop.
For workshops with three-phase motors, add phase monitoring. A motor running on two phases will destroy itself quickly, and neither a standard protector nor a stabiliser will necessarily catch that.
What neither device does
Neither provides backup power. When the supply fails entirely, a protector disconnects and a stabiliser has nothing to correct. If you need continuity through an outage, that is a UPS or generator — a separate purchase and a separate decision.
See Over & Under Voltage Protectors and Circuit Protection.
Sizing each device correctly
A protector is sized by the current of the circuit it sits on. A 63A unit protects a board drawing up to 63A; fitting one rated below the actual load will overheat the device itself. Check the main incomer rating and match or exceed it.
A stabiliser is sized by the load it feeds, in VA or kVA, and needs headroom for motor starting. A stabiliser rated exactly at an air conditioner's running load will be driven into overload every time the compressor starts. As a rule, allow at least double the running rating for anything with a motor.
Common mistakes worth avoiding
- Fitting a stabiliser and assuming you are protected. Many stabilisers pass through voltages outside their correction range rather than disconnecting. Read the specification.
- Setting the protector's window too wide. A range of 140V to 300V will almost never trip, which defeats the purpose.
- No reconnection delay. Without one, an unstable supply cycles the load on and off repeatedly, which is harder on a compressor than the sag itself.
- Protecting the appliance but not the board. One DIN-rail protector covers every circuit downstream, usually for less than a single per-appliance unit.
Frequently asked questions
Can I use both together?
Yes, and it is a common arrangement. The protector covers the property; the stabiliser covers the equipment that must keep running.
Which is better for an air conditioner?
A protector is usually sufficient and much cheaper. A compressor that shuts off during a sag is not harmed; one that keeps running on low voltage is.
Do stabilisers waste electricity?
They consume a small amount in operation. On a whole-property scale that adds up, which is another reason protectors are preferred at the board.