IEC 60364 Table 48A

ProMbrooke:

Higher rated circuits has a much lower R1+R2, producing voltage drop on the transformer and in turn a lower touch voltage whereby disconnection can be longer without worry of physiological harm. 

That is a huge assumption - particularly for public TN-S supplies - that most of the supply resistance is in the transformer and line conductor.


The "standard" figures for 100 A supplies doesn't support this view:


TN-C-S, Ze = 0.35 Ohm


TN-S Ze = 0.8 Ohm


Both supplies have the same line conductor and same transformer, so the difference, > 50 %, must be the distributor's protective conductor.


So, you really aren't going to be able to reduce the potential touch voltage in TN-S systems of 100 A or less below 115 V nominal.


Touch voltages can be better in PME systems.


Alternatively, if you actually do have exposed-conductive-parts, inside buildings with TT, these present the lowest touch voltages in an earth fault. Sadly, outdoors they produce the highest touch voltages. But then again, you're far more likely to have at least two RCDs in series (RCD main switch and an RCBO for the final circuit) to help you in a TT system ...


Perhaps we'd just better all go TT?

ProMbrooke:

Higher rated circuits has a much lower R1+R2, producing voltage drop on the transformer and in turn a lower touch voltage whereby disconnection can be longer without worry of physiological harm. 

That is a huge assumption - particularly for public TN-S supplies - that most of the supply resistance is in the transformer and line conductor.


The "standard" figures for 100 A supplies doesn't support this view:


TN-C-S, Ze = 0.35 Ohm


TN-S Ze = 0.8 Ohm


Both supplies have the same line conductor and same transformer, so the difference, > 50 %, must be the distributor's protective conductor.


So, you really aren't going to be able to reduce the potential touch voltage in TN-S systems of 100 A or less below 115 V nominal.


Touch voltages can be better in PME systems.


Alternatively, if you actually do have exposed-conductive-parts, inside buildings with TT, these present the lowest touch voltages in an earth fault. Sadly, outdoors they produce the highest touch voltages. But then again, you're far more likely to have at least two RCDs in series (RCD main switch and an RCBO for the final circuit) to help you in a TT system ...


Perhaps we'd just better all go TT?