Can someone let me know the science behind this please. I’ve been told that if there is a fault on a circuit the ZS values in the regs are there to give ADS in a time that is not going to cause considerable harm. My question is if disconnecting times don’t comply what is the dangers that arise I know it’s physics but have seen marshalling bars carrying current through earthing conductors all day and we don’t get a shock of them. Thank you for you help in advance guys just want to clear up some unanswered questions.
Remember you only get a shock if you touch two things at different voltages simultaneously so that current flows through you - the live line working chaps have this off to a tee! (as do birds sitting on the overhead lines)
It is also the reason older engineers put one hand behind the back or in a pocket when poking something that may just be live - in the days of maintenance on valved TVs with a few hundred volts of HT, this simple habit was literally a life saver. (the 20 odd kV EHT was less dangerous, as it was incapable of supplying high current for a long time, and therefore while really painful for the short time the strored charge was dumped, was not so risky as the mains derived HT that could supply a good fraction of an amp all day)
In the case of your earthy bus-bars, assuming you are also earthed more or less, then when you touch them there is no voltage difference across your body to drive a shock current.
Touch the earthy bus bar and a live one with the other hand however, and its all over....
Remember you only get a shock if you touch two things at different voltages simultaneously so that current flows through you - the live line working chaps have this off to a tee! (as do birds sitting on the overhead lines)
It is also the reason older engineers put one hand behind the back or in a pocket when poking something that may just be live - in the days of maintenance on valved TVs with a few hundred volts of HT, this simple habit was literally a life saver. (the 20 odd kV EHT was less dangerous, as it was incapable of supplying high current for a long time, and therefore while really painful for the short time the strored charge was dumped, was not so risky as the mains derived HT that could supply a good fraction of an amp all day)
In the case of your earthy bus-bars, assuming you are also earthed more or less, then when you touch them there is no voltage difference across your body to drive a shock current.
Touch the earthy bus bar and a live one with the other hand however, and its all over....
