16th Ed Theory: Supplementary Equipotential Bonding back to MET not allowed?

[JohnW2]

I seemed to stupidly overlook and forget that a fault will take the path of least resistance ...

As I'm sure you know, that's not strictly true - or, at least, not the whole of the story. If there are two or more parallel paths, then more of any current (due to a fault or otherwise) will go though 'the path of least resistance' than through any of the other paths, but the total current will be shared by all of the parallel paths, in inverse proportion to their respective resistances (essentially just a basic application of Ohm's Law).

Kind Regards, John

 

[eveares]

Yes quite, as I said;

current will go through the supplementary bonding conductor going back to the MET under a fault condition due to it being a parallel path in addition to the joined up CPC's of the bathrooms circuits

Current will of course go back through all parallel paths, including the CPC's of all circuits linked to the SEB, but due to the human resistance being much higher than 0.01Ω, very little will go through a person touching two or more simultaneously accessible parts in the bathroom due to the two or more parts being at very near the same impedance (i.e. 0.01Ω difference etc... between the parts.)

100A x 0.01Ω = 1V = Nowhere near enough potential difference do cause a dangerous amount of current to flow through someone. At an impedance of 0.01Ω, the current would have to exceed 5000A for touch voltage greater than 50V to exist between two or more simultaneously accessible parts in the bathroom.

 

[EFLImpudence]

Current will of course go back through all parallel paths, including the CPC's of all circuits linked to the SEB, but due to the human resistance being much higher than 0.01Ω, very little will go through a person touching two or more simultaneously accessible parts in the bathroom due to the two or more parts being at very near the same potential (i.e. 0.01Ω difference etc... between the parts.)

Just a slight correction.

100A x 0.01Ω = 1V = Nowhere near enough potential difference do cause a dangerous amount of current to flow through someone. At an impedance of 0.01Ω, the current would have to exceed 5000A for touch voltage greater than 50V to exist between two or more simultaneously accessible parts in the bathroom.

That's it.

Even if you touch a conductor carrying 5000A, it is still the voltage with the resistance of your body and your earth connection which determines the amount of current flow through your body.
No earth connection at all - no current.

 

[eveares]

Just a slight correction.

I do not remember typing "impedance". Quite right that a potential difference (aka voltage) of 1V between the simultaneously accessible parts is no concern at all in terms of being a danger to ones self.

 

[JohnW2]

Current will of course go back through all parallel paths, including the CPC's of all circuits linked to the SEB, but due to the human resistance being much higher than 0.01Ω, very little will go through a person touching two or more simultaneously accessible parts in the bathroom due to the two or more parts being at very near the same impedance [potential] (i.e. 0.01Ω difference etc... between the parts.).

Quite so - and that, of course, is/was the whole point of SEB. Without such bonding, the potential between two exposed-c-ps which were connected to the MET via different CPCs could, under appropriate fault conditions, theoretically approach the supply voltage (for a very short period of time, before a protective device hopefully operated).

Kind Regards, John