I'm not intending to continue these epic length posts, save to say that your understanding of main earthing and main bonding along with LP systems leaves a lot to be desired.
Yes, coming from the same person who makes claims with certainty regarding NEC and American installs which every American electrican knows is absolutely untrue. That speaks a lot just by itself.
I dont know all that much about BS7671 or British installs, so I never make any solid claims. Imagine how I would look on this forum if I did. Rather I just keep an open mind.
You are also blindly accepting that the supply from a network operator be it TN-S or TNC-S is always going to have an adequate Ze value, and even if it hasn't, bonding it to a properties extraneous metal service pipes will solve the problem, ...it won't!!
In theory I am, but then again I know it will in 99.99% of American services. I know My neutral is intact. I know the short circuit values. I know its size. I know the distance to the transformer in most cases. If I call POCO for equipment AIC (short circuit) ratings saying a phase to neutral short will produce 18,000 amperes in a 200amp 120/208Y commercial service do I really need to factor in Z? 18,000 amperers will trip the main instantaneously, and will be more than enough current for branch breakers.
At the branch level, we use full size earth wires. Even if I extend a 3.31mm2 (12 gauge) circuit 350 feet to the point voltage drop is over 5%, I can calculate the short circuit current knowing the impedance of the conductors. A phase to ground short all the way at the end of a 350 foot run will produce several hundred amps. An American 20amp breaker trips in 1/60 of a second at 200amps, 10/60 of a second at 100amps. The fault is removed very quickly.
Because of our over engineered earth wires and bonding, even when the fault is happening the voltage rise is well below 80 volts to remote earth.
And again, even if POCOs neutral broke during the fault (it wont), even though every metal surface will be 120 volts to remote earth, all metal within the structure will be zero volts because its bonded together. Floor to plumbing, zero volts. Oven to fridge, zero volts.
I suggest two things to you, firstly purchase a Earth Loop Impedance tester and test those incoming supplies to properties, i think you could well be surprised at the values it shows you, for both Ze and Zs.
This I will do, anyways its nice to know if the EGC is intact at the branch level.
Study the functions and reasons for main bonding and Equipotential Zones, as well as the importance of N-E connections to TNC-S service supplies. Have you ever heard of PME (Protective Multiple Earth) earthing system?? It's basically a TNC-S earthing supply, but has multiple N-E points along it's length from the TX. On an overhead supply system that would generally be a N-E link with an earth electrode ever 3rd or 4th pole.... A typical PME earth in the UK has an accepted max Ze of 0.35 ohms, while a TN-S earth has a typical max of 0.80 ohms. (note, these figures are given as typical by the DNO'S, and not set in stone)
I'm going to try and attach a copy of the UK's Regulations, it's not the current copy, but more than good enough for you to understand some of the points we have been discussing.
Will, do, always willing to learn
(Can't upload the pdf maybe if you give me your email address via the PM system here i can send it to you direct...)
I will send over an Email address.
