Open Transition or Closed transition ATS.

A closed transition ATS means that for a short time period the generator will be connected to both the load and your primary source, and is only useful when both sources are available. The generator/ATS control must be capable of synchronizing with your primary source.

A loss of the selected source will still result in an interruption of power. If you already have a UPS downstream of the ATS protecting your critical loads, then a closed transition is not necessary.

Your UPS should have a separate maintenance bypass scheme, one that does not directly involve your transfer switch. I do not know what you are intending to achieve, but a closed transition switch will not prevent a loss of power to your critical load while your UPS is in bypass.

In the last sentence do you mean open transition?

I guess I should have been more specific. A closed transition during an unplanned power outage. During such an event, power is already lost before transfer takes place.

Hi Lendog,

You are right that there will be momentary interruption during a utility shutdown, however, the main intention of using a closed transition type ATS is to follow NFPA 110 during a planned power shutdown with two available power sources wherein the generator would seamlessly take over the loads from utility source and prevent momentary power interruption such as loss of data, or flickering of lights etc..ATS which has mechanical parts needs monthly tune up to check its functionality and likewise to test the generator operation capability to take over the critical load from the UPS battery in case of power utility failure. This would give test run reliability of the electrical system.

Thanks for your comment,

Acer