AJJewsbury:

Thus, I am advocating for a touch voltage limit of 25 volts be established for wet locations with a disconnection time of at most 0.2 seconds for 230 volt supplies.

Curiously, we seemed to have exactly that for some special locastions back in the 16th Ed (1991) - specificslly construction sites (section 604) and Agricultural and Horticultural Premises (section 605) - so somewhere along the line it seems that someone decided that 0.4s plus additional protection (e.g. 30mA RCDs) was an improvement.


Perhaps oddly the same requirements didn't appear for bathrooms or pools at the time, even though there was no requirement for RCDs (although 230V was banned from the wettest part of those locations and supplementary bonding was required).


It's perhaps a mute point anyway, since most final circuits are protected by B-type or C-type MCBs (or similar in RCBOs) - so disconnection will be within 0.1s anyway (and 0.04 if a 30mA RCD is functioning) - so a change to 0.,2s in the regulations perhaps wouldn't result in any significant safety improvement in practice.


   - Andy.

I agree in full in that MCBs will always trip in a few cycles when sized to a 0.4s Zs. However, if fuses are employed a gap could be present, hence why I think the regs should cover all possible scenarios.  


 

AJJewsbury:

Thus, I am advocating for a touch voltage limit of 25 volts be established for wet locations with a disconnection time of at most 0.2 seconds for 230 volt supplies.

Curiously, we seemed to have exactly that for some special locastions back in the 16th Ed (1991) - specificslly construction sites (section 604) and Agricultural and Horticultural Premises (section 605) - so somewhere along the line it seems that someone decided that 0.4s plus additional protection (e.g. 30mA RCDs) was an improvement.


Perhaps oddly the same requirements didn't appear for bathrooms or pools at the time, even though there was no requirement for RCDs (although 230V was banned from the wettest part of those locations and supplementary bonding was required).


It's perhaps a mute point anyway, since most final circuits are protected by B-type or C-type MCBs (or similar in RCBOs) - so disconnection will be within 0.1s anyway (and 0.04 if a 30mA RCD is functioning) - so a change to 0.,2s in the regulations perhaps wouldn't result in any significant safety improvement in practice.


   - Andy.

I agree in full in that MCBs will always trip in a few cycles when sized to a 0.4s Zs. However, if fuses are employed a gap could be present, hence why I think the regs should cover all possible scenarios.