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.

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)

I don't bother the output of the TX. I struggle what to use for the primary site of it. The max output current is pretty much 2x16A (2 sockets) so 32A total. This unit is 3.3kVA so we can calculate as 3300kVA / 230V = 14A so 16A MCB type D should be fine to protect this device then. Am I right?

Yes, though of course the D type (needed for inrush) will need a lower loop impedance, so it may be that your Zs does not permit, and you need RCD or RCBO primary to get prompt disconnection from earth faults. That will depend on the earthing arrangements and length of circuit it is supplied by.

And you should consider the secondary earthing arrangements, as if you intend to plug in things like 110V power tools, it is, as others have noted, not the standard arrangement.

And just because there are two unfused 16A sockets on a supply capable of delivering 32A or so does not make it sensible, unless  you have good control of what is being plugged in. If by dint of trailing leads and in-line splitters 25A of load ended up on one side only, and the other side was unloaded,  one socket would be overloaded and nothing would trip off..

Mike.

PS Mind you I suppose its no worse than using an unfused 32A to 16A splitter cable -  So perhaps I'm too old and fuddy-duddy about this sort of thing. The folk selling these marvels give no warning about fusing down or load management after all...
  
All 32A in and twice 16A out for 110/230 and 400V as seen for sale by outfits that seem to be proper shops.