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ITGlossary · Protection and installation
Short Circuit
An unintended low-resistance connection between conductors that causes a sudden, dangerous surge of current.
Technical level:Intermediate
When the phase conductor comes into contact with neutral or earth through a very low resistance, for example due to damaged insulation, moisture or a wiring error, the current rises abruptly to many times its normal value. Such a short circuit can melt cables, start a fire and destroy equipment within a fraction of a second.
Fuses and circuit breakers are designed to interrupt it almost instantly. A UPS has electronic short-circuit protection on its output; when running on battery, the inverter can supply only a limited fault current, so it usually shuts down its output to protect itself.
A practical tip: if a UPS cuts its output with a short-circuit indication, disconnect all loads and reconnect them one by one to find the faulty device.
Related terms
- Circuit ProtectionDevices such as fuses and circuit breakers that open the circuit on overcurrent or short circuit to prevent damage.
- Ground FaultAn unintended flow of current from a live conductor to earth or to a device’s metal casing.
- Emergency Power Off (EPO)A safety feature that allows immediate shutdown of power to connected systems in an emergency.
- 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.
- Overcurrent ProtectionA system designed to interrupt excessive current to protect UPS and loads.
- OverloadA condition where the connected load exceeds the UPS’s rated output in VA or W.