Hi Everyone,
I've been reading up on earthing/grounding practices, and this bit keeps confusing me. I will quickly run through my understanding of the return path for current in a domestic situation:
In normal conditions, current flows in the live and neutral conductors, and the return path is generally provided back to the substation through these conductors as a low impedance connection (alternating flow and return of course in an AC circuit). In this situation, though, the neutral line is also connected to the separate earthing conductor at the main panel (if we consider this to be a TN-S system), which is then connected to the earthing rod at the house. According to wire regulations (at least where I am in the UK) the impedance of the ground path back to the substation through the ground rod to the substation's earth stake is required to be below a certain value (for 32A circuits, this may be <5 Ohm for example) in order for overcurrent devices to trip in the appropriate time frame. To me, that is quite low resistance indeed.
Given this low impedance path back to the substation from the house's grounding rod, is this path not constantly used for flow and return of normal operating current? If the path is indeed low impedance, then why do we need a separate neutral conductor as a flow/return into our houses? I know that this does occur in certain situations and is labelled Single Wire Earth Return (SWER), but I am struggling to understand why we don't always do this if wiring regulations require us to maintain a low impedance path back to the sub-station through the Earth.
In addition, if we consider an earth fault on a conducting surface of equipment, because the ground and neutral conductors are connected, fault current must be flowing through both the Earth loop path as well as the normal neutral return. Is this correct?
I've been reading up on earthing/grounding practices, and this bit keeps confusing me. I will quickly run through my understanding of the return path for current in a domestic situation:
In normal conditions, current flows in the live and neutral conductors, and the return path is generally provided back to the substation through these conductors as a low impedance connection (alternating flow and return of course in an AC circuit). In this situation, though, the neutral line is also connected to the separate earthing conductor at the main panel (if we consider this to be a TN-S system), which is then connected to the earthing rod at the house. According to wire regulations (at least where I am in the UK) the impedance of the ground path back to the substation through the ground rod to the substation's earth stake is required to be below a certain value (for 32A circuits, this may be <5 Ohm for example) in order for overcurrent devices to trip in the appropriate time frame. To me, that is quite low resistance indeed.
Given this low impedance path back to the substation from the house's grounding rod, is this path not constantly used for flow and return of normal operating current? If the path is indeed low impedance, then why do we need a separate neutral conductor as a flow/return into our houses? I know that this does occur in certain situations and is labelled Single Wire Earth Return (SWER), but I am struggling to understand why we don't always do this if wiring regulations require us to maintain a low impedance path back to the sub-station through the Earth.
In addition, if we consider an earth fault on a conducting surface of equipment, because the ground and neutral conductors are connected, fault current must be flowing through both the Earth loop path as well as the normal neutral return. Is this correct?