In short. A wide-input-range stabiliser keeps output steady across a larger supply swing, for example 280 to 480 V on a 415 V system. At low input the current rises for the same power, so the rated output may reduce. Always specify from measured minimum and maximum voltages.
Why range matters
Standard stabilisers handle moderate swings. Weak supplies, remote feeders and generator-fed sites can go beyond. If input leaves the range, the unit cuts off or passes the voltage through, and the load sees the problem.
Low-voltage effect
I = P ÷ (√3 × V × power factor)
For the same power, lower voltage means higher current. Windings and contacts heat more. Makers therefore rate wide-range units with reduced output at the lowest input. Check the output-versus-input curve.
| Input voltage (illustrative, 415 V system) | What to check |
|---|---|
| Near nominal | Full rating |
| Low end | Reduced rating; current rise |
| Beyond range | Cut-off or bypass; load unprotected |
Specifying
- Record voltage for at least a week; note minimum at heavy load.
- Add a margin beyond observed extremes.
- Read the maker’s curve for output at the low end.
- Size kVA so the derated output still covers demand.
Accuracy trade-off
A wider range can mean slightly wider output tolerance or slower correction. Check against load sensitivity. See servo stabilisers.
Generator supply
Generator voltage varies with load steps and regulation. Frequency changes affect motors inside the stabiliser. Confirm the frequency window. See DG and stabiliser.
Illustrative example
A remote pumping station sees 300 V during irrigation peaks. A normal-range unit trips. A wide-range unit holds 415 V but is derated at 300 V, so the engineer selects a higher kVA model that still carries the pumps at the low end.
A worked specification example
A site records the following over two weeks on a 415 V three-phase supply: minimum 290 V at evening peak, maximum 455 V late at night, with a connected load of 90 kVA of motors and lighting.
- Define the required input window with a margin below 290 V and above 455 V, for example 270 to 475 V, subject to what the maker offers.
- Read the maker’s rating curve. A wide-range unit may be rated at full output only from a higher voltage, with reduced output below it.
- At 290 V, current for the same power is about 1.43 times what it is at 415 V (415 ÷ 290). Windings and contacts must carry that.
- Select the kVA rating so that the derated output at 270 V still covers the demand.
Cost and accuracy trade-off
| Choice | Benefit | Cost |
|---|---|---|
| Narrow range, tight accuracy | Precise output, lower price | Trips or bypasses outside range |
| Wide range, moderate accuracy | Rides through extremes | Higher price, derated at low input |
| Wide range plus upstream correction | Best of both | More equipment |
Behaviour outside range
Know what the unit does at the edges: trip, pass through, or hold at the last tap. For critical loads, the safe behaviour is usually to alarm and either trip with notice or bypass in a controlled way, rather than silently pass a damaging voltage.
Verify on site
- Use a variable supply or the real supply at extremes to see how the unit behaves.
- Check the alarm and cut-off set points.
- Record output voltage at the lowest input available.
Longer-term fix
A stabiliser protects the load, but the weak supply remains. Where the problem is a fixed feeder, a conversation with the utility about the supply, or a dedicated transformer tap change, may reduce the range needed.
The master engineering question
At the lowest supply voltage and highest load, does the stabiliser still deliver the required output without overheating?
What to send us
Send voltage records and load. Send your application details.
Questions engineers ask
Is wider always better?
No. It costs more and may derate; choose from data.
What happens outside range?
The unit trips or bypasses, depending on design.
Will it fix a weak grid?
It protects the load, but the supply fault remains.
Can I use one on a generator?
Yes, if range and frequency suit.
Values are illustrative. Use manufacturer curves.