Why ATS (Auto Transfer Switch) Required Overlapping Neutral (Make Before Break)

Please find the sketch, propose to solid connection for the neutral of transformer source.

You would use "make-before-break" only if you are transferring the load between two powered busses that are synchronized if your load cannot suffer a momentary loss of power.

"A closed transition transfer switch (CTTS) is also called a make-before-break transfer switch.

A typical emergency system uses open transition, so there is an inherent momentary interruption of power to the load when it is transferred from one available source to another (keeping in mind that the transfer may be occurring for reasons other than a total loss of power). In most cases this outage is inconsequential, particularly if it is less than 1/6 of a second.

There are some loads, however, that are affected by even the slightest loss of power. There are also operational conditions where it may be desirable to transfer loads with zero interruption of power when conditions permit. For these applications, closed transition transfer switches can be provided. The switch will operate in a make-before-break mode provided both sources are acceptable and synchronized. Typical parameters determining synchronization are: voltage difference less than 5%, frequency difference less than 0.2 Hz, and maximum phase angle between the sources of 5 degrees. This means the engine driving the generator supplying one of the sources generally must be controlled by an isochronous governor."

https://en.wikipedia.org/wiki/Transfer_switch

Fire alarm systems are particularly sensitive to any variation in voltage,and a brief interruption may result in a zone setting an alarm condition.This usually requires a manual reset.

"The sweet taste of a low price is forgotten when the bitter taste of regret is in your mouth."..unknown

"There is always someone in the world who can make something a little worse, and sell it a little cheaper, and those who consider price only are this person's lawful prey." _{- John Ruskin.}

sure, but now the world is changed, the winner is those who put something not required in the specification to sell his product. which is enough to scare the client who trust the specification as bible.

Fire alarm system usually provided with battery back to avoid any mal operation during momentary power outage or fluctuation.

thank you,

Most of the local electricity boards not allow the parallel operation, how ever they insist the momentary parallel operation of neutral only. This is my question why need make before break only for neutral. floating neutral for a 60millisecond can damage an equipment?

If the neutral is broken on one of the derived single phase circuits, the voltages can surge or dip,depending on the devices using the neutral as a return for unbalanced loads.

The single phase circuits now become in series with each other instead of parallel,resulting in constant current and variable voltage through each device.

I have seen devices destroyed by a broken neutral,such as computers,monitors,and automated machinery power supplies.

of course its true sir, definitely it will happen if the system loss neutral during normal operating condition. But my question is regarding the load transfer from generator to normal source. ie, if the normal power is restored, the generator acb will be tripped (load will loose power supply for a moment) immediately will be connected to normal supply. So the neutral may loose earth connection for a maximum 100milli seconds. means there will be resdual voltage or back feed from the load for this duration? if so i think if we give a time delay of 2seconds for re-transfer the load side may become dead. So that there will be no surge.

If the circuit is disconnected from a supply for however long and for whatever reason, then no voltage is present in it, by definition.

A neutral is only a power-carrying conductor that is held close to earth potential.

Any inductive load will generate a Counter- EMF when the power is interrupted,even briefly.The faster the interrupt,the greater the Counter-EMF;If the neutral is open,the EMF can be up to double the normal voltage level,when the neutral is used to carry the unbalanced load on single phase circuit.This is enough to destroy some solid state devices.

Thank you for the right answer.

So this was a test, eh?

sorry, thanks for the right guidance.