I agree that it won't always be dominated by the transformer, but as you place current on the output terminals voltage will begin to drop. 230 vs 200 vs 150 volts between the X1 and X0 terminals is enough to make a significant time difference in the body graph when dealing with a hand to foot resistance of resistance of 1000 ohms. Especially when the IEC assumes that body resistance itself will change based on contact voltage.


Supply transformers are becoming larger through out the world and I think this is why IEC-60364-4-41 now requires the 0.4 second disconnection time be extended socket circuits up to 63 amps.


Regarding the UK that would be correct, however it still works out by leaps and bounds vs the minimum requirments of BS7671 or table 41.1.  Disconnection times (0.4 and 5s) can not be met or achieved via the thermal element in UK/EU MCBs and hence rely on the magnetic (solenoid) trip function. This means that even the max listed EFLI values for type B-D 125 amp MCBs will result in disconnection faster than 0.1 seconds. This leaves us with fuses/devices 125 amps and over which typically have a Zs of <0.25 ohms. Going by ohms law 0.2 gives us 265kw or 1,150 amps with an infinite source. A 250kw rated heater being placed across any phase and earth will result in a measurable drop in output voltage on a 5% Z 166kva transformer (assume the 500kva unit is a bank of 3 166kva units). Transformer voltage regulation is excellent at unity power factor, however sharply declines with lagging power factor. Reactance begins to dominate as you go up in wire size, so where as a 1mm2 lighting circuit will be seen as almost a purely resisitive load (during a fault), a circuit over 63 amps will dedicate at least half or more of its fault current to maintaining the magnetic field around each conductor. Consider current division and open over head conductors in the fault loop and XL dominates substantially.


Try this, play around with the slides in relation to lagging loads vs unity loads to give you an idea:


  https://voltage-disturbance.com/power-engineering/transformer-voltage-regulation/



Lastly consider that a final circuit is Zs=Ze+(R1+R2)... part of a whole when wiring a building...  meaning sub circuits from board to board are rarely run to their maximum EFLI having to of a low enough Z to allow for the final circuits to be long enough to hit all the devices through out. 


In summary faults will either disconnect in less than 0.1 seconds, or result in significant voltage drop through the transformer making fault point voltage to remote earth minor.

I agree that it won't always be dominated by the transformer, but as you place current on the output terminals voltage will begin to drop. 230 vs 200 vs 150 volts between the X1 and X0 terminals is enough to make a significant time difference in the body graph when dealing with a hand to foot resistance of resistance of 1000 ohms. Especially when the IEC assumes that body resistance itself will change based on contact voltage.


Supply transformers are becoming larger through out the world and I think this is why IEC-60364-4-41 now requires the 0.4 second disconnection time be extended socket circuits up to 63 amps.


Regarding the UK that would be correct, however it still works out by leaps and bounds vs the minimum requirments of BS7671 or table 41.1.  Disconnection times (0.4 and 5s) can not be met or achieved via the thermal element in UK/EU MCBs and hence rely on the magnetic (solenoid) trip function. This means that even the max listed EFLI values for type B-D 125 amp MCBs will result in disconnection faster than 0.1 seconds. This leaves us with fuses/devices 125 amps and over which typically have a Zs of <0.25 ohms. Going by ohms law 0.2 gives us 265kw or 1,150 amps with an infinite source. A 250kw rated heater being placed across any phase and earth will result in a measurable drop in output voltage on a 5% Z 166kva transformer (assume the 500kva unit is a bank of 3 166kva units). Transformer voltage regulation is excellent at unity power factor, however sharply declines with lagging power factor. Reactance begins to dominate as you go up in wire size, so where as a 1mm2 lighting circuit will be seen as almost a purely resisitive load (during a fault), a circuit over 63 amps will dedicate at least half or more of its fault current to maintaining the magnetic field around each conductor. Consider current division and open over head conductors in the fault loop and XL dominates substantially.


Try this, play around with the slides in relation to lagging loads vs unity loads to give you an idea:


  https://voltage-disturbance.com/power-engineering/transformer-voltage-regulation/



Lastly consider that a final circuit is Zs=Ze+(R1+R2)... part of a whole when wiring a building...  meaning sub circuits from board to board are rarely run to their maximum EFLI having to of a low enough Z to allow for the final circuits to be long enough to hit all the devices through out. 


In summary faults will either disconnect in less than 0.1 seconds, or result in significant voltage drop through the transformer making fault point voltage to remote earth minor.