Reason for having multiple earths

[FreshmanNewbie]

I have been going through the TNCS electrical system of grounding and noticed that this system has Multiple earths in the PEN conductor.

Refering to this link

However, I am not able to understand the purpose of the multiple earths. What is the purpose of it and how does multiple earth help in an adverse situation?

 

[dick_freebird]

It may be that the showing of multiple earths is meant to
represent the mechanical. An assembly made of metal
components would want to explicitly "earth" each piece, not
depend on mechanical fasteners for electrical qualities
(especially if left to corrode over time).

 

[D.A.(Tony)Stewart]

This has not a thing to do with multiplanetary seaches in the universe.

More “earths” distributed, provide more escapes for lightning to avoid your house power being affected by resistance, inductance and high current discharges protected by grid circuit breakers. If there is an arc, the follow-on SCR-effect of the grid energy can be far worse. Thus distributed “earth grounds” are essential to a more reliable grid.

The link cited a certain topography of AC networks and this …
The advantage of using the combined conductor in this way is that it provides a low impedance return path which ensures rapid disconnection of the supply under fault conditions. For a TN-C-S system, supply distributors’ specify a maximum external fault loop impedance Ze of 0.35 Ω.

In electronics, we say “ground” for any local reference** of 0 V, whether it is floating like our planet or an isolated supply. it is just a reference to some unknown but expected, relatively low impedance “voltage source”. In this case, Grid neutral is bonded to “protected earth (PE) ground” at source. These have different specifications for different nodes on the network for maximum resistance.

When a fault must trip a breaker quickly, a lower resistance will increase the grid fault current bypass to earth ground and the breaker will trip faster. This is safer than distributing the very high voltage from lightning.

** We say earth or ground is 0V , but in reality, any current on a path away from this point must have some voltage. We just assume it is below tolerance, by design, until it isn’t.