Prospective Fault Current

[pushrod]

Max Zs confirms your disconnection times, not minimum PFC.

.

Your max Zs will give you your min PFC though (I was thinking of similar things i have been asked at college and wondering if the OP had been asked the same). I know it is Zs figures that are quoted in appendix 2 of the OSG though not PFC's.

Thanks for the 3rd point though i hadn't thought of that

 

[WayneL]

To be honest, this discussion is a bit irrelevant as your PFC is most likely
to be your PSCC - (ie. L - N or L - L) and you're not gonna be calculating
that, so Ze/Zs/R1+R2 don't come into it.

 

[Jurasic Spark]

It's all very well quoting guidance note 3, care to explain how you'd do it?

You'll have noticed GN3 doesn't tell you how.

Ok then how would you answer this type of exam scenario or what about if it was real world scenario?

During a PIR on small comercial unit it is unpracticable to isolate the main switch, how can you ascertain a value of Ze? You have tried enquiry but no one will answer the phone?

 

[GaryM]

Either volunteer for out of hours or put it down as a limitation.

 

[Jurasic Spark]

Either volunteer for out of hours or put it down as a limitation.

There are no out of hours, the place runs 24/7.
Can't you elaborate on your limitation?

 

[andyb]

Ok then how would you answer this type of exam scenario or what about if it was real world scenario?

During a PIR on small comercial unit it is unpracticable to isolate the main switch, how can you ascertain a value of Ze? You have tried enquiry but no one will answer the phone?

Measure it.

The only limitation is that you can't remove the earth for a true reading, you put this down under limitations.

 

[Jurasic Spark]

Measure it.

The only limitation is that you can't remove the earth for a true reading, you put this down under limitations.

Or CALCULATE it using Uo and your measured Pefc and record this as a limitation.

 

[WayneL]

Ok then how would you answer this type of exam scenario or what about if it was real world scenario?

During a PIR on small comercial unit it is unpracticable to isolate the main switch, how can you ascertain a value of Ze? You have tried enquiry but no one will answer the phone?

Keep trying the phone - coz if they won't let you open the main isolator, you shouldn't have the cover off the board in
the first place

Failing that, measure it with the earthing conductor connected and mark as limitation.

Everyone is arguing the ---- but no-one has come up with an answer yet - How can you
possibly calculate it accurately?

Or CALCULATE it using Uo and your measured Pefc and record this as a limitation.

If you've measured Pefc, you might as well have measured Ze while your there and mark Lim

 

[Jurasic Spark]

Keep trying the phone (and what do you think they'd say if they answered it?)- coz if they won't let you open the main isolator, you shouldn't have the cover off the board in
the first place

Well if your engaged in this sort of work lets assume you have the level of competence to do it. So not a problem. Or else how you going to measure Pfc??

Failing that, measure it with the earthing conductor connected and mark as limitation.

Everyone is arguing the ---- but no-one has come up with an answer yet - How can you
possibly calculate it accurately?
How accurate does it need to be??


If you've measured Pefc, you might as well have measured Ze while your there and mark Lim

Well you can re-decorate while your there as well but why do things you don't need to ??

 

[SirKit Breaker]

My point was that you can't calculate Ze.

I thought the same, as it says on the Installation Cert "by measurement or enquiry".

 

[GaryM]

I thought the same, as it says on the Installation Cert "by measurement or enquiry".

And if it's enquiry they'll probably quote 0.35 or 0.8 ohms!

 

[Guest123]

And if it's enquiry they'll probably quote 0.35 or 0.8 ohms!

They do.