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ITGlossary · Electrical units
Inrush Current
The initial surge of current required when electrical equipment is first powered on.
Technical level:Intermediate
When a power supply with capacitors, a transformer or a motor is switched on, it briefly draws a current many times its normal value. In electronic power supplies the peak lasts a few milliseconds, while motors, such as those in fridges, pumps and air conditioners, often draw several times their rated current for longer.
For a UPS this means its rating must cover not only normal consumption but also this peak. Otherwise the UPS goes into overload, transfers to bypass, or shuts down when running on battery.
Do not switch all loads on at once after an outage. In a rack with many servers, a staggered start through programmable outlets or a PDU avoids overload. For loads with motors, ask for technical advice before choosing a size.
Questions that mention it
All frequently asked questionsCan an AVR support air conditioners or refrigerators?
Yes, provided it has the right power rating. Be careful with loads that have a high inrush current.
Related terms
- Noise (Electrical)Unwanted high-frequency disturbances on the supply voltage, e.g. from motors or power supplies, which UPS systems and line conditioners filter out.
- Single-phase PowerAn electrical system with one alternating current (AC) voltage phase, commonly used in homes and offices.
- Hardwired (Terminal Block) ConnectionPermanent connection of the UPS input or output by an electrician, with cables screwed into a terminal block instead of plugs and sockets, usually on higher-power UPS units.
- Peak LoadThe highest amount of power drawn by connected equipment during operation.
- DC VoltageRefers to the direct current (DC) voltage level, typically that of a UPS battery.
- IEC C13/C14 ConnectorsStandardised pair of connectors rated up to 10 A under IEC 60320, found on UPS outputs and on the power supplies of computers, servers and monitors.