gkenyon:

ProMbrooke:

Regarding touch voltage it is difficult to control as is. Reduced size CPCs, contact with earth, ect all present a voltage that is higher than assumed in Table 41.1. 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. 

 

1. It's always difficult to control touch voltage to Earth with a CPC. In fact, in TN-S systems, without main protective bonding it's difficult to control anyway. Unless you're advocating the distributor and/or consumer put additional electrodes in to help.
   
    

• I'm not really in agreement with you 100 % on the "wet location" argument. What kind of wet location, and what are the circumstances of the users? There's more to this than a simple table. As per previous posts, it depends on what you're wearing and whether saltwater wet is the issue or not. Under worst-case wet condition, sadly 0.2 s is not adequate. Worth having a look at IEC/TR 60479-5 This is the reason BS 7671 has other measures in places like bathrooms and swimming pools - including removing the hazard of AC mains completely by prohibiting it in some Zones. If you are erring on the side of caution to 100 % guarantee safety, it's goodbye to AC mains full stop I'm afraid.

There will always be voltage to remote earth, TT being the worse at full mains. Assuming full size CPC, touch voltage will be half of Uo. 110% of 230 = 253 volts, divided by two equals 126.5 volts. Going by IEC 61200-413 Table A gives us a disconnection time of 0.33 seconds, at for Table C.1 0.17 seconds.


The thing is, we know what the conditions typically are. In addition to the body having an internal resistance of about 300 ohms, we can also gauge worse case skin conductance down to 5% of the population. A reasonable worse case value can be obtained somewhere around 500 ohms. 1,500 for dry locations. When compared to the IEC's body graph disconnection times can be derived for both areas.


Pools are the most demanding conditions, in addition to the fact an open PEN can bring the pool to full mains relative to remote earth, so bonding does have its place here for anyone in the water or climbing out of it.   


I understand my argument is somewhat moot in that MCBs will typically open in a few cycles due the short circuit solenoid, however in cases where fuses are employed longer disconnection times may be present for the fuse's max loop impedance.         

gkenyon:

ProMbrooke:

Regarding touch voltage it is difficult to control as is. Reduced size CPCs, contact with earth, ect all present a voltage that is higher than assumed in Table 41.1. 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. 

 

1. It's always difficult to control touch voltage to Earth with a CPC. In fact, in TN-S systems, without main protective bonding it's difficult to control anyway. Unless you're advocating the distributor and/or consumer put additional electrodes in to help.
   
    

• I'm not really in agreement with you 100 % on the "wet location" argument. What kind of wet location, and what are the circumstances of the users? There's more to this than a simple table. As per previous posts, it depends on what you're wearing and whether saltwater wet is the issue or not. Under worst-case wet condition, sadly 0.2 s is not adequate. Worth having a look at IEC/TR 60479-5 This is the reason BS 7671 has other measures in places like bathrooms and swimming pools - including removing the hazard of AC mains completely by prohibiting it in some Zones. If you are erring on the side of caution to 100 % guarantee safety, it's goodbye to AC mains full stop I'm afraid.

There will always be voltage to remote earth, TT being the worse at full mains. Assuming full size CPC, touch voltage will be half of Uo. 110% of 230 = 253 volts, divided by two equals 126.5 volts. Going by IEC 61200-413 Table A gives us a disconnection time of 0.33 seconds, at for Table C.1 0.17 seconds.


The thing is, we know what the conditions typically are. In addition to the body having an internal resistance of about 300 ohms, we can also gauge worse case skin conductance down to 5% of the population. A reasonable worse case value can be obtained somewhere around 500 ohms. 1,500 for dry locations. When compared to the IEC's body graph disconnection times can be derived for both areas.


Pools are the most demanding conditions, in addition to the fact an open PEN can bring the pool to full mains relative to remote earth, so bonding does have its place here for anyone in the water or climbing out of it.   


I understand my argument is somewhat moot in that MCBs will typically open in a few cycles due the short circuit solenoid, however in cases where fuses are employed longer disconnection times may be present for the fuse's max loop impedance.