High Zs for circuit with metal conduit earth

[EFLImpudence]

Just measure the resistance from socket to MET with long lead - and deduct lead.



Anyway, R2 of 0.6 + R1 of 0.12 + Ze of 0.2 = Zs 0.92

 

[endecotp]

"just measure the resistance" requires a meter that has a usefully-low resistance range.

Where does your R1 = 0.12 come from?

 

[EFLImpudence]

OK if you do not have suitable meter.

R1 = r1/4

 

[endecotp]

If I have a conduit circuit where R1 = 0.12 and R2 = 0.60, is this anything to worry about?

Is the higher reading from the Zs meter, 1.31, within the typical variability?

 

[EFLImpudence]

If I have a conduit circuit where R1 = 0.12 and R2 = 0.60, is this anything to worry about?

I would think the conduit reading should be lower than 0.6 but it's probably creeping up with age.
0.92 is alright.

Is the higher reading from the Zs meter, 1.31, within the typical variability?

Mmm. Not really. If anything it might be lower than 0.92 because of parallel paths - although there may not be any.

I think you can ignore the 1.31.
One of the methods of determining Zs is merely to measure R2 (as you have) and R1 and add them to Ze.

The original figures of r1 and r2 would seem to be correct - more or less the same.
You have confirmed R2.
If Ze is 0.2 - typical around here.

So, that just leaves the 1.31 as the odd one out.




Out of interest - is the other circuit you mentioned NOT in conduit?

 

[endecotp]

The other circuit is also in conduit.

 

[EFLImpudence]

Oh. Ok.

More mystery. Has a CPC been fitted?

You have these values.

r1 = 0.54
rn = 0.54
r2 = 0.72
(R1+R2) = 0.28
Zs = 0.40

He has treated r2 as a ring on this one - almost (72+54)/4 = 31.5

Other than that the figures are plausible.



I guess the only way to find out is to have someone do the tests again.