EL
BG
DE
ES
FR
ITGlossary · Power quality
Transfer Switch
A manual or automatic switch that connects the load to one of two sources, such as the grid and a generator, never both at once.
Technical level:Intermediate
A transfer switch connects the load to one of two or more sources, for example the mains or a generator. In the manual version the user operates it, while an automatic transfer switch (ATS) detects the outage, sends a start signal to the generator and transfers the load once its voltage has stabilised.
A generator usually needs from a few to a few tens of seconds to take over. That is why in critical installations the UPS bridges this gap and the ATS feeds the UPS input from the generator.
The switch must have a mechanical or electrical interlock so that the two sources are never connected at the same time. Installing it is a job for a licensed electrician.
Related terms
- GeneratorAn engine-driven alternator that produces electricity when the grid fails, often started automatically through an ATS.
- ATS (Automatic Transfer Switch)A device that automatically moves the load from the grid to a generator during an outage and back again when grid power returns.
- Offline (Standby) UPSA UPS that leaves the load on the mains and switches to battery only when the mains fails, with a short transfer time; the simplest and cheapest topology.
- Static SwitchA thyristor-based switch with no moving parts that transfers the load between inverter and mains within a fraction of a cycle.
- Input Voltage WindowThe range of mains voltage within which a UPS keeps powering the load from the grid without switching to battery.
- Power ConditioningTechniques such as EMI/RFI filtering, surge protection and AVR that correct voltage problems before they reach the load.