Why power quality matters
The UK mains supply is not as clean as it looks. Even without a full blackout, your equipment is exposed dozens of times a day to voltage disturbances that can crash systems, corrupt data and shorten hardware life. The IEC recognises nine distinct categories of power disturbance, and a well-specified UPS addresses most of them.
The common disturbances
- Blackout / outage — complete loss of mains. A UPS provides battery backup until the mains returns or a generator starts.
- Sag (dip) — a short drop in voltage, often caused by large motor starts or grid switching. Can reset servers and stall equipment.
- Swell (surge) — a brief voltage rise, typically from load shedding. Stresses insulation and components.
- Spike / transient — a very fast, high-energy overvoltage from lightning or grid events. Can destroy power supplies instantly.
- Undervoltage / overvoltage — sustained out-of-range voltage, common in remote or heavily loaded networks.
- Frequency variation — changes in mains frequency, significant for generator-backed sites.
- Harmonic distortion — waveform pollution from non-linear loads (SMPS, drives), causing overheating and neutral currents.
- Noise — high-frequency interference injected onto the line by nearby equipment.
- Notching — periodic voltage dips from SCR or rectifier switching.
How a UPS and conditioning fix them
An online double-conversion UPS regenerates the waveform, so sags, swells, spikes, frequency variation, harmonics and noise are all removed before they reach the load. For sites with chronic voltage issues, a voltage stabiliser or voltage optimiser can be added upstream to correct sustained under/over-voltage and reduce energy consumption.
Frequently asked questions
What is the most common power problem?
Voltage sags (dips) are the most frequent disturbance, often caused by large loads starting on the same circuit or grid switching events.
Can a UPS protect against lightning?
A UPS clamps most transients and spikes, but a direct or nearby lightning strike carries enormous energy. Always combine a UPS with proper building surge protection at the distribution board.
What is harmonic distortion?
Distortion of the mains waveform caused by non-linear loads like switch-mode power supplies. It causes overheating in transformers and neutrals. Online UPS isolate the load from it.
Do I need a voltage stabiliser as well as a UPS?
Only if your site suffers sustained under- or over-voltage. A UPS corrects brief events; a stabiliser handles continuous out-of-range voltage and can cut energy bills.