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The maximum permissible disconnection time is 0.4 s in TN system. Why and from where this value (0.4 s) is obtained?
Former Community Member
The maximum permissible disconnection time in in the event of a short circuit between a phase conductor and a body or protective conductor or a protective-neutral conductor is 0.4 s in TN system. Does anybody know this value (0.4 s) obtains from where? How this value is obtained?
Protective bonding is accounted for in the calculation for touch voltage. I agree that there are variables and perhaps some arbitrary assumptions. The touch voltage used in the calculation is taken from;
Ut = mxcxU /m+1
Where Ut is the prospective touch voltage, m is the ratio of protective conductor resistance to phase conductor resistance m=R2/R1, c is similarly the relationship between the internal impedance and overall impedance c= R1+R2/Zs (taken as an arbitrary 0.8), U is 1.1 x Uo
I should say, by the way, all this is taken from the Commentary on the 16th Edition by the excellent Mr Paul Cook.
Protective bonding is accounted for in the calculation for touch voltage. I agree that there are variables and perhaps some arbitrary assumptions. The touch voltage used in the calculation is taken from;
Ut = mxcxU /m+1
Where Ut is the prospective touch voltage, m is the ratio of protective conductor resistance to phase conductor resistance m=R2/R1, c is similarly the relationship between the internal impedance and overall impedance c= R1+R2/Zs (taken as an arbitrary 0.8), U is 1.1 x Uo
I should say, by the way, all this is taken from the Commentary on the 16th Edition by the excellent Mr Paul Cook.
