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ITGlossary · Power quality
Undervoltage
A sustained drop of mains voltage below normal that can cause malfunctions or overheat motors.
Technical level:Basic
Unlike a momentary voltage dip (sag), undervoltage lasts from a few minutes to hours. It often appears at the end of long lines, in remote areas or at peak times. On the European 230 V grid, the EN 50160 standard treats a deviation of up to ±10% as normal, which puts the lower limit at about 207 V.
Motors draw more current to do the same work and heat up, while electronic devices may restart unexpectedly. A line-interactive UPS or a voltage stabilizer (AVR) boosts the voltage without using the battery, whereas an offline UPS switches to battery at every undervoltage.
If your UPS often goes to battery even though the power has not failed, measure the voltage at the socket; the cause is often persistent undervoltage, not a faulty UPS.
Related terms
- Voltage DropA decrease in voltage level in a circuit due to resistance or high load.
- BypassA path that feeds the load directly from the mains, without protection, when the UPS is overloaded, faulty or under maintenance.
- IK Rating (Impact Protection)Scale from IK00 to IK10 under IEC 62262 that shows how much impact energy the enclosure of an electrical device can withstand.
- 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.
- IEC C19/C20 ConnectorsPair of connectors rated up to 16 A under IEC 60320, used on higher-power UPS units, rack PDUs and servers or switches with high-consumption power supplies.
- IP Rating (Ingress Protection)Two-digit code under IEC 60529 in which the first digit shows protection against dust and solid objects and the second against water.