Is there any way of getting the PEFC if you only have the Ze?

[Ashley2]

Absolutely no need to apologise in my opinion. Everyone has an opinion.

Thank you for your response. And with reference to my initial query, my conversation with D Skelton was spot on, he put me right & I could have kicked myself for having lost that aspect:

D Skelton: (8). “PEFC is calculated using voltage and Ze only, forget the info about the 100A protective device because it seems to be confusing you and throwing you off”.

My response was:
Ashley2: (11). Yes, its not the 100A protective device, its the Icn value, "& for the majority of applications the prospective fault current at the terminals should not exceed this value". It is ohms law, KISS should be the motto in 2391.

The above remark was in response to my input into the exam question, namely that I should have kept it simple, in terms of answering this part, & I should have kept to Ohms law, instead of gallivanting into other areas. As far as I was concerned the matter had been concluded, thanks to D Skelton & IQelectrical.

 

[D Skelton]

As always there will be differences of opinion.

I was always taught to use the Ze {measured} +(R1+R2) {again measured} and record the calculated results method.

The reason my mentor taught me this method, was if your calculated (two measured results added together) complied, then any parallel paths which lowered the Zs was a bonus, but not guaranteed.
You were actually measuring and calculating the worst case results, which were likely (but not guaranteed) to be better in reality, so if your results complied they could only get better, this he said was proper testing and proving compliance.
Likewise if you just measured your Zs, things could change later leaving you with a non compliant circuit.

On my own jobs I do the two measurements and calculate method and record this result, but still check the measured Zs just to double check that everything is ok.

I have worked on sites where they have wanted the actual measured Zs, but on the other hand I have been boll*cked on yet another site (same firm, different gaffer) where my Zs has been lower than the Ze (due to parallel paths), so it seems you cannot win, as always he who pays the piper calls the tune.

I agree 100%. When determining Zs, I believe calculation is always best because like you said, you are working out what the Zs would be in the worst case scenario with no parallel paths.

When working out PEFC however, I was always taught that measurement is best because you want to include all the parallel paths to find out what the worst case scenario is.

 

[spark 68]

When working out PEFC however, I was always taught that measurement is best because you want to include all the parallell paths to find out what the worst case scenario is.

Agreed,
:yes:

 

[D Skelton]

my conversation with D Skelton was spot on, he put me right

thanks to D Skelton & IQelectrical.

In future, there is a little 'Thanks' button at the bottom left hand corner of every post. Just tap that if you wanna say thanks to someone for writing a helpful and informative post

In all seriousness though I'm glad you finally grasped the concept, when I first started studying I found things hard to grasp, hell I'd even go as far to say that most of us on here find one or more things hard to understand still. We all have our weaknesses and we're all still learning however one thing I've noticed that seperates the men from the boys in this game is that the men still have a keen interest in learning about our work no matter how experienced they are. The boys however know it all already (or at least think they do)! So my advice is never give up your quest for more knowledge! The hungrier you are for it, the more seriously you will be taken IMHO.

I'd also agree with the KISS acronym, one sure way of getting yourself in a right old mess in this line of work is overthinking things! We've all done it!