Touch Voltage Calculation

Oh Boy - More education for me required I'm afraid - 


I have always understood that when we talk of touch voltages, we are dealing with a situation where ADS may be a problem or increased danger posed from the specific circumstances in play, and additional protection is installed in the form of Main and Supplementary protective equi-potential bonding. (Note 3 from 415-2: Supplementary protective bonding may involve the entire installation, a part of the installation, an item of equipment or a location.) A bathroom is a good example of a location where touch voltages may be important but this is a micro example of what could be a much larger system. 


I've always associated touch voltage and bonding, and touch voltage and supplementary equi-potential bonding as two synchronous items. BS7671 415.2 area. 


IT systems it also gets important (Not that I've ever seen or worked with an IT system)


But I assume if you're standing at a pump station out in the middle of nowhere then touch voltages between earthed metal equipment such as the body of the motor control centre and tera forma may pose an issue. A rod is almost guaranteed to be involved here so ground voltages should also rise in sypmathy with a fault current I guess?


I also assume that on a large manufacturing plant where metal pipe work travels 100s of meters across the ground and men (possible animals) and equipment are all able to come in contact with that pipe work and earth - what happens then? Would you put earth stakes effectively at regular intervals to lower the touch voltage between the pipework and earth? I guess so. 


Every day's a school day if you try; I learn something new every day here......


Kind Regards 

Tatty


To me when talking of touch voltages, the important calculation is: R needs to be less than or equal to 50V/Ia in AC systems where Ia is the operating current in amps of the protective device or for RCDs I delta n (The mA rating of the RCD) or  the over current devices 5 second operating current, (which, for a normal final circuit - this 5 second operating current figure can be taken from the tables on the time/current graphs in Appendix 3 BS7671)


Am I on the correct lines here?

Oh Boy - More education for me required I'm afraid - 


I have always understood that when we talk of touch voltages, we are dealing with a situation where ADS may be a problem or increased danger posed from the specific circumstances in play, and additional protection is installed in the form of Main and Supplementary protective equi-potential bonding. (Note 3 from 415-2: Supplementary protective bonding may involve the entire installation, a part of the installation, an item of equipment or a location.) A bathroom is a good example of a location where touch voltages may be important but this is a micro example of what could be a much larger system. 


I've always associated touch voltage and bonding, and touch voltage and supplementary equi-potential bonding as two synchronous items. BS7671 415.2 area. 


IT systems it also gets important (Not that I've ever seen or worked with an IT system)


But I assume if you're standing at a pump station out in the middle of nowhere then touch voltages between earthed metal equipment such as the body of the motor control centre and tera forma may pose an issue. A rod is almost guaranteed to be involved here so ground voltages should also rise in sypmathy with a fault current I guess?


I also assume that on a large manufacturing plant where metal pipe work travels 100s of meters across the ground and men (possible animals) and equipment are all able to come in contact with that pipe work and earth - what happens then? Would you put earth stakes effectively at regular intervals to lower the touch voltage between the pipework and earth? I guess so. 


Every day's a school day if you try; I learn something new every day here......


Kind Regards 

Tatty


To me when talking of touch voltages, the important calculation is: R needs to be less than or equal to 50V/Ia in AC systems where Ia is the operating current in amps of the protective device or for RCDs I delta n (The mA rating of the RCD) or  the over current devices 5 second operating current, (which, for a normal final circuit - this 5 second operating current figure can be taken from the tables on the time/current graphs in Appendix 3 BS7671)


Am I on the correct lines here?