One of the features of double conversion Uninterruptible Power Supplies is that they contain a “Bypass” circuit. This means that in the event of a UPS failure they will circumvent power around the UPS and continue to provide power to the load. One point to note here is that the UPS will continue to provide power even when it may be switched off!
This is different to the operation of line interactive and standby types. You press the OFF button, and then the load is switched off. Press it on again, and there it is, back again.
Now with online systems, generally they will start up in bypass. So you connect power and lo and behold, you have power to the load. Don’t leave it at that!! You must remember to switch on the inverter or you will not be protected.
The UPS will indicate Bypass operation, and will indicate inverter operation when switched on. It’s a feature of online systems that will extend reliability of power to the load, but only if the correct operation of the unit is observed. After all, what’s the point of protecting your system only to leave it switched off?
