After speaking with electricians in my place and finding this info below I am going to use MCB type D as a protection of this isolation transformer not RCBO previously considerated.

"Will and RCD work with an isolation transformer"...

But note that they're talking about RCDs on the secondary side of the transformer - not the primary (feed) - and if yours ends up CTE (as above) the bit about No Earth isn't quite the case either. RCD/RCBO on the primary side would have to be decided by the usual rules (e.g. soft cables concealed in walls, run in some special locations, fed via a plug & socket, or high Zs (e.g. TT systems)) for the primary circuit.

  - Andy.

True. So should I treat this circuit same as regular 230V socket circuit and fit RCBO for this purpose? I am confused now. There 2 x 16A sockets on the output of this TX with no MCBs dedicated.

Below is the unit I am thinking to use.

I don't suppose they bother with MCBs on the output, because there's one on the supply.  For a 230V to 110V step down, the input current will be pretty close to half the output current.  So if the correct MCB is specified for the input, it will protect the output too.

should I treat this circuit same as regular 230V socket circuit and fit RCBO for this purpose?

RLV sockets don't need 30mA RCD protection in the same way that 230V ones do (the RLV system with only 55V to earth makes it comparatively safe even without RCDs - see the last bit of NOTE 1 to 411.3.3) - but depending on the situation an RCD still might be needed for the primary circuit for other reasons - it depends on the circumstances.

An RCBO on the primary wouldn't provide additional protection to the sockets on the secondary side anyway (since L-PE faults on the secondary would be seen as L-N fault current on the primary). Depending on Zs etc (on which the transformer will have an influence) you might want and RCD on the secondary to achieve 5s disconnection time for ADS on the sockets. But again it's all mights and maybes.

   - Andy.

(edited to add 2nd bit)

should I treat this circuit same as regular 230V socket circuit and fit RCBO for this purpose?

RLV sockets don't need 30mA RCD protection in the same way that 230V ones do (the RLV system with only 55V to earth makes it comparatively safe even without RCDs - see the last bit of NOTE 1 to 411.3.3) - but depending on the situation an RCD still might be needed for the primary circuit for other reasons - it depends on the circumstances.

An RCBO on the primary wouldn't provide additional protection to the sockets on the secondary side anyway (since L-PE faults on the secondary would be seen as L-N fault current on the primary). Depending on Zs etc (on which the transformer will have an influence) you might want and RCD on the secondary to achieve 5s disconnection time for ADS on the sockets. But again it's all mights and maybes.

   - Andy.

(edited to add 2nd bit)