The ATS lacks the fault-interrupting capacity.

old field guy

There are many varieties of transfer switch available.
One version I have serviced used two molded case breakers with a rear mounted, approved, mechanical interlock and motor operators on the breakers.
Basically an ATS may be designed with any breaker or switch that is capable of non-manual operation.
There are very versatile cable based mechanical interlock devices available.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

There are ATS' approved for service entrance duty. That would include fault capability.
If you are seeing an ATS at a lower price it is likely that the ATS under consideration lacks some needed features such as fault interrupting capacity.
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

There are also ATS that have an integrated panel w/ CBs.

NickParker (Electrical)(OP)26 Aug 24 15:46
'..Can an Automatic Transfer Switch be used in place of a tie breaker in a Main-Tie-Main with ATS (Auto transfer scheme) for low voltage applications?'.
1. Automatic Transfer Switch by definition, it acts like a switch. It does NOT break automatically, on over current during closing or in closed position.
2. On the market, there are ATS* using normal/standard Breakers, with mechanical and electrical interlocked included etc.
Note: a) these normal/standard breakers can be MCBs, ACBs with LSIG.. settings etc.
b) as these are standard breakers, they can have all the features/characteristics of a Breaker; i.e. automatically breaking on over-current while closing or breaks in closed position.
3. The main difference is, ATS does NOT open on over-current while combination of MCB/ACB includes the automatic opening on over current.
4. There could be some cost and size difference. Selection would be based on the application.
Che Kuan Yau (Singapore)

I would go with the main-tie-main and add mechanical interlocks, (if not already present) motor operators and some control circuitry.
Call it an ATS or something else as long as it does the job.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

We installed several for station service applications in our generating stations over the last 5 years. All of them were basically switched molded case breaker type, and several were service entrance rated.