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ITGlossary · UPS technology
Bypass
A path that feeds the load directly from the mains, without protection, when the UPS is overloaded, faulty or under maintenance.
Technical level:Intermediate
There are two kinds of bypass in a UPS. The static bypass works automatically: if the UPS is overloaded or has an internal fault, the load is transferred instantly straight to the mains so that it does not go down. The maintenance bypass is manual and lets a technician isolate the UPS for repair while the loads stay powered.
While the UPS is on bypass, the loads take power directly from the mains, without filtering and without battery backup. An outage at that moment will shut them down.
Practical tip: for critical installations, choose an external bypass panel, which allows the UPS to be removed completely. And do not leave the UPS on bypass longer than necessary; check the alarms and the reason it switched over.
Questions that mention it
All frequently asked questionsCan a UPS run without batteries?
Some models can run temporarily without batteries, in bypass mode only, but they offer no protection against power outages.
Related articles
Related terms
- Static BypassAn electronic path inside the UPS that instantly and automatically transfers the load to the mains on overload or internal fault.
- UndervoltageA sustained drop of mains voltage below normal that can cause malfunctions or overheat motors.
- OverloadA condition where the connected load exceeds the UPS’s rated output in VA or W.
- Cold Start FunctionA feature that allows a UPS to be started directly from the battery without utility power.
- 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.
- Capacity SystemParallel UPS units that share the load with no spare unit (N configuration), so the failure of one unit overloads the rest.