Although many of these breaks in power last for only a few milliseconds, it is always possible to experience an extended loss of power, often referred to as a blackout, or sometimes an outage.

Even very short breaks can cause sensitive electronic equipment such as personal computers, servers, printers, modems, hubs and routers, to crash, lock up or reboot. Though this is widely understood, there are many other power quality problems that can also result in equipment malfunction or failure.

Surges and spikes are very short bursts (a few milliseconds at most) of very high energy voltage. They can cause wear or acute damage to electronic equipment, and can be very damaging over extended periods.

Surges in excess of 6kVA are not unknown. They can be caused by electrical storms or can be created by inductive motors, such as those found in equipment like refrigeration units, lifts or escalators. Fluorescent lighting can also be responsible for short duration spikes. If a surge voltage rises above the tolerance level of the power supply unit (PSU), it will activate its cut-out to protect itself, potentially triggering an IT system crash. Surges can also lead to gradual degradation of electronic components, such as printed circuit boards, causing processor damage, memory loss and data corruption.

Sags are one of the more common forms of poor power quality. A sag is experienced when the mains power voltage drops below the normal supply level, typically for several cycles. This can cause data processing hardware to fail, lock up or reboot. Power supply units can also be stressed as they attempt to deliver the required power and can overheat leading to other problems at a later date. A common cause of sags is when electrical devices, which have a high demand, are on the same local circuit. These can include industrial machinery and air conditioning units.

Brownouts are caused by an extended reduction in mains power below the normal power supply voltage. This situation can sometimes persist for a period of days. The effect on delicate electronic equipment is very similar to sags, and power supply units can be severely damaged, due to the extended nature of the fault.

Electrical noise is a high frequency disturbance which can disrupt electrical circuits and potentially damage them. Some possible causes of electrical noise are radio transmitters, flickering lighting, faulty cabling and switchgear. Harmonics are voltage or current multiple waveforms, of the basic frequency. It can cause distortion of the mains supply voltage, overheating of switchgear, transformers and wiring circuits within the fabric of the building. It can also cause problems and failures to equipment being fed by the same supply.

By placing a double conversion UPS between the incoming mains and sensitive electrical equipment, the UPS will 'condition' the power and remove threats of malfunction. With poor power quality having the potential to cause substantial problems, the UPS performs two functions. Firstly, it cleans the power, but it is also there, should the power fail completely, to supply back-up power. This provides for an orderly shutdown of the electrical equipment it is protecting, or bridging the gap between power failure and a generator taking up the load.