ELI pass point.

[ericmark]

Yes the calculations are not really valid other than say a single farm house in the wilds, multi-houses and solar panels mean it is only approximant, however the question is still the same, if due to changing the cables used by simply selecting which fuses are inserted the DNO can change the ELI at the DNO head, is there an official allowance to be made for the change in Ze? If the DNO state the Ze will not go below xΩ and the measurement on the day is x-yΩ should the Zs have y added to it to see if it passes?

OK with nearly every circuit now RCD protected it is not now so important, but it is the circuits like a cooker supply which can still be without RCD protection which are using high current so are the more likely to have a problem with any Ze changes.

 

[SimonH2]

As another thought, what happens to prospective fault currents when you start adding embedded generation ? I assume it has "complex" effects, but generally increases the current available - you've now more power sources than just the substation and it's load side fuses to the street cabling. Wasn't this one area of concern when the craze for mass distributed generation got going ?

As an aside, I've seen the effects of a change of feed. Some years ago at work, we saw several ENWL vehicles pull up at the substation that's just across the road from the office. We saw someone walk round the corner out of sight, and after a while we noticed the lights dim - I recall me and my manager looking at each other and the lights with that "will it, won't it" (power go off) look that we didn't need to speak.
Then we saw someone open up the fuse cabinet and after a short time the lights brightened up again (the voltage was still a little down on normal). So it seems they'd put links in round the corner and taken the fuses out from our normal supply - my guess is that while we had a "dual supply" there may have been some imbalances causing the lowered voltage.
As I had logging from the UPS, we could see clearly on the graph what the voltage did - I can't find it now, sorry.

The whole process we could see was a van came round and sucked the oil of out the 11kV switchgear, some blokes did something inside, then the oil van came round and refilled it, then they put us back on the normal supply - voltage dropped when they put the fuses in, and went back to normal when the took the temporary links out. I gather there had been some problems with a particular bolted connection so they had a program to go round and check them all (or some specific subset - perhaps anything installed during a time window).

 

[JohnW2]

As another thought, what happens to prospective fault currents when you start adding embedded generation ? I assume it has "complex" effects, but generally increases the current available ....

The maximum current which could flow from the solar panels' inverter would surely be insignificant compared with the hundreds of amps of fault current that would/could flow through the DNO's network, wouldn't it?

Kind Regards, John