Talk:TT system - Principle

For fault current it's stated as "IΔn ≤ 50/20 = 2.5 A so that a standard 300 mA RCD will operate in about 30 ms without intentional time delay and will clear the fault where a fault voltage exceeding appears on an exposed-conductive-part." In this calculation (2.5 A fault current) substation earth electrode resistance was not taken into account. Shouldn't have it been 50/(10+30)?