Protection & wiring for 110V site transformer

Question

Is RCBO required as a protection device for 110V 3.3kVA site transformer with 2x16A sockets or MCB would be fine? 
 I am also questioning the wiring from that snapshot. As far as I am aware there is 1.5mm2 (max 2.5mm2) wires used inside the device. 
 Also, why 4mm2 chosen for the wiring between the fuse and the isolator? 
 Is 16A would be definitely enough in this scenario?

AJJewsbury · Accepted Answer

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)

Protection & wiring for 110V site transformer

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