A little assistance required regarding earth sizing.

[EFLImpudence]

The over protective device for the 10mm T+E sub-main is a 50A 1361 fuse. When i phoned the helpful bloke at the NICEIC he said to use BS88-2 fuse to work out the prospective fault current as per table in the bible. Therefore using 220A as that figure, and working out the adiabatic equation you get the figure of 4.91mm. Hence why it has been TT'd (i presume).

220A is the figure for 5 seconds but you can't get 220A - you only have 64 (230/3.57).

The second D.B has been tapped off of the top of the first D.B's RCD and into its own RCD upfront.

So the supply to the second doesn't flow through the first.

The earth has been segregated in the first D.B (as it's now a TT). The cpc for the ongoing feed to the second D.B has been terminated into the earth bar in the first D.B.

Do you mean the second DB's earth is connected to the electrode?

I have talked to the client and i am going to TT the second D.B and Obviously segregate the incoming earth in that board.

Is it not already? Dependent on the answer to the previous question.

I can assure you that it really is a true EFLI!!
Will be interesting to see what figure o get when i bang the first rod in for the second D.B!

What will you do if it is more than 3.57?

Job done.

Yes, indeed.

What is the Ze at the origin?

I'm going for a beer!

That's always good.

 

[Davisss]

Hi EFLI.

Last post of the day for me.

I take your first point.

The supply to the second doesn't flow 'through' the first. It simply goes into the supply side of the rcd and then off into the supply side of the second rcd.

The second D.Bs earth is indeed connected to the first D.Bs electrode.

If it's more than 3.57 then I shall bang another one in. It should be very similar as its not too far away and the owner assures me that only one electroe was used!

Haven't tested the Ze at origin as of yet but will do when I go back.

Now, time for more beer and downtime.

Cheers!

 

[JohnW2]

If I understand correctly what you mean by "Zn", I think it should be half that figure - a PSCC of 434 A implies (at 230V) an L-N loop impedance of 0.53Ω, So the N, or the L, part of that will be 0.265Ω, won't it? However, I'm not sure what point you were making about "Zn".

I use Zn as the symbol for the Neutral loop; is that not normal?

From my position of inexperience, I can't speak for 'normal', but I've never seen it before - I was guessing that (by analogy with, say, Rn) you were probably talking about the impedance of the neutral conductor back to the tranny. In any event, what you were talking about was the L-N loop impedance - why are you calling that "the Neutral loop" (rather than, say, "the Line loop")??

I was pointing out that the distance of the buildings cannot be that far.

Ah, I see.

Kind Regards, John

 

[EFLImpudence]

I was guessing that (by analogy with, say, Rn) you were probably talking about the impedance of the neutral conductor back to the tranny.

No, analogous of Ze.

In any event, what you were talking about was the L-N loop impedance - why are you calling that "the Neutral loop" (rather than, say, "the Line loop")??

For the same reason as we call it Earth loop.

 

[JohnW2]

I was guessing that (by analogy with, say, Rn) you were probably talking about the impedance of the neutral conductor back to the tranny.

No, analogous of Ze.

Ah. I've always been led to believe that the "e" of "Ze" referred to "external", not "earth"?

In any event, what you were talking about was the L-N loop impedance - why are you calling that "the Neutral loop" (rather than, say, "the Line loop")??

For the same reason as we call it Earth loop.

Only colloquially, surely - as someone with your username should know, it should be Earth Fault Loop Impedance, shouldn't it? However, I suppose that "NFLI" would be analogous to that - but, again, I have to say that I've never previously seen it used!

Kind Refards, John

 

[EFLImpudence]

Ah. I've always been led to believe that the "e" of "Ze" referred to "external", not "earth"?

Well, yes but the Line Impedance is external as well.
I don't think 'Line Impedance' and 'Loop Impedance' (as used by Fluke) is particularly logical or self-explanatory.
Perhaps I have made up my own terms.
What symbol or abbreviation do you use for the Line Impedance?

In any event, what you were talking about was the L-N loop impedance - why are you calling that "the Neutral loop" (rather than, say, "the Line loop")?

Well. it is the 'Earth Loop' and 'Neutral Loop'.
The Line is involved in both; the Neutral isn't 'Line'

Only colloquially, surely

Is colloquially not allowed?

as someone with your username should know, it should be Earth Fault Loop Impedance, shouldn't it?

It should but not always is written in full.

However, I suppose that "NFLI" would be analogous to that - but, again, I have to say that I've never previously seen it used!

It would be more logical and if Ze is EFLI what would be NFLI?

However, my brother does not post on here.

 

[JohnW2]

I don't think 'Line Impedance' and 'Loop Impedance' (as used by Fluke) is particularly logical or self-explanatory. ... Perhaps I have made up my own terms. ... What symbol or abbreviation do you use for the Line Impedance?

Good question, but I think the answer is that I would not use a 'symbol or abbreviation' - I would talk about "L-N loop impedance" and then qualify that (as with Ze) if I were just talking about the 'external' part thereof (i.e. L-N loop impedance as measured at origin of installation)

In any event, what you were talking about was the L-N loop impedance - why are you calling that "the Neutral loop" (rather than, say, "the Line loop")?

Well. it is the 'Earth Loop' and 'Neutral Loop'. The Line is involved in both; the Neutral isn't 'Line'

Indeed, as I went on to concede ...

However, I suppose that "NFLI" would be analogous to that - but, again, I have to say that I've never previously seen it used!

It would be more logical and if Ze is EFLI what would be NFLI?

See above. Mind you, we obviously need to be careful about precision of terminology - whilst Ze is "an EFLI", so is Zs !

However, in the context of this thread, I now understand what you meant - which is what matters.

Kind Regards, John