Couple of testing questions ?

[pc1966]

So how is the r2 measured on a board with parralel paths on the final circuits ?

It is unusual to see a RFC with much in the way of parallel paths, unless metal-clad sockets on a metal building, etc, or perhaps conduit system that has mounting also on metal structures. In such cases R2 is likely to be far lower than R1 and you circuit zs domainated by the cable R1 and (maybe) supply Ze.

It is unusual to need R2 on its own, so if you do the "figure of 8" test with the links at the board (and not linked to the MET there) then your range of R1+R2 measured at the sockets gives you a worst-case value to get max Zs (from Ze + R1 + R2) to compare to the OCPD limiting Zs for disconnection time.

But you can always estimate R2 as (r2)/4 for the same reasons. However if you are unsure of the pysical layout or can't unlink CPCs at the board (e.g. conduit system, etc) then you can measure your worst (R1+R2) at the various sockets and estimate R2 by subtracting the R1 = (r1)/4

 

[Mikegh]

View attachment 93697
( Electrical Safety and Testing Standards - RECI Presentation - https://analytical-testing.ie/blog/electrical-safety-testing-standards/ )

I've had a read through your tests, and they are basically the same idea as what we have to do.
All I can say is that if it were a UK sheet, the sub main CU get's it's own sheet, and you would record the earth loop impedance at the incomer of the sub main DB at the top of the sheet.
Then for each circuit you would record either just the resistance of the circuit CPC (R2) on the circuit itself, or the combined resistance of the Live and CPC (R1+R2).
Then we also note the Zs which is the total, either measured like your test 8 "Line/Earth fault loop impedance" or calculated by adding the incomer impedance to the R1+R2.
I've never seen one of your test sheets though so hopefully someone local can comment!



If the CPC is not a wire, then the R2 can be measured with a long wander lead, or a temporary link made at the circuit end and R1+R2 measured at the consumer unit. Just the same as if it were a wire really.
Disconnecting bonding and incoming earth at the sub-main (obviously with it isolated) can remove the parallel paths from the measurements.

Makes sense giving each board its own sheet, that's the way the test sheets are done here

Incoming fault loop + final loop and you can record your protective conducter resistance or R1+R2

That probably answers my query about max protective conducter resistance reading

 

[timhoward]

I'm still not quite clear on the ring finals

If I want the max resistance of the CPC on a ring final cct.

What's the exact method/formula for that ?

Fig8 test will measure the exact answer, including any damaged sockets with poor contacts on the pins.

End-to-end tests measuring r1,rn and r2 (small letters) and calculating (r1+r2)/4 will tell you what the answer is assuming all sockets are in perfect condition.

 

[LastManOnline]

2) Can someone explain simply the L-E loop test for ring circuits

Now that your question has been expertly answered your next challenge will be to locate a ring circuit within a hundred mile radius of your home. You might just find a few in Dublin, but they are rare.
In case you are planning to install any be aware they are forbidden in kitchens (the very area they are most valued in the UK). I suspect (but Don, t support) that they are nearing the electrical exit. You may also find you will be the only spark(Irish based) in 2022 to do so.
To test they are a royal pain in connection with their simpler cousin the radial.

 

[timhoward]

To test they are a royal pain in connection with their simpler cousin the radial.

I'm glad you found this thread!
I did a board change recently that had no ring circuits as the owner simply disliked them. There were in fact far too many radial circuits, he had one just for the kettle socket, and I used 9 RCBOs for a simple 3 bed house.
But anyway, it was very nice (and odd) not having any RFCs to test and I couldn't quite believe how quickly I got it all tested.

 

[LastManOnline]

radial circuits...... , and I used 9 RCBOs

Radial circuits and rcbo, s (dual pole?) my dream CU

But anyway, it was very nice (and odd) not having any RFCs to test and I couldn't quite believe how quickly I got it all tested.

"Oi lad, s I believe we have a potential convert"

 

[nicebutdim]

To test they are a royal pain in connection with their simpler cousin the radial.

In general terms this is true, but I can't help wondering if Irish regulations stipulate how radial circuits must be installed or amended.

If it is mandated that such circuits follow a strictly linear form , then all is simple. If not; what's to stop future additions being taken from random points, with obvious testing issues arising as more than one end point can exist?

 

[timhoward]

Oi lad, s I believe we have a potential convert"

In many ways I already am.
We need to remember that the ring final circuit was designed in the 40's anticipating a shortage of copper when houses had far fewer sockets arranged generally in large squares. It was true then that you could serve a large area with a smaller gauge cable therefore using less total copper. I honestly don't think this logic stacks up today.

While I obviously maintain these circuits every day I don't often install new ones.

 

[SparkySy]

I quite like the ring final circuit myself.
During testing some from late 70s to around early 80s and untouched ones (no alterations or additions) around my area, generally they are in very good condition apart from the odd loose terminal or knackered outlet!
The main problem with them is people who don't quite have the skills to work on them but think they do (imho)
I think we should still try to reserve resources be that copper or the ever mounting pile of pvc that we keep adding to, none of these things are infinite!
Although I do like and use radial circuits as well, I think there is still a purpose for ring circuits and a time and place to use them.
Sy

 

[Mikegh]

Now that your question has been expertly answered your next challenge will be to locate a ring circuit within a hundred mile radius of your home. You might just find a few in Dublin, but they are rare.
In case you are planning to install any be aware they are forbidden in kitchens (the very area they are most valued in the UK). I suspect (but Don, t support) that they are nearing the electrical exit. You may also find you will be the only spark(Irish based) in 2022 to do so.
To test they are a royal pain in connection with their simpler cousin the radial.

Yes of course the ring circuit and ring final still have a place in industry /commercial and power distribution

Not so much in domestic imo although with the price of copper ?

As you say we're(ire) using multiple radials now in kitchens and utility, years ago it was a couple of rings

As you say the testing is a little complex for a basic circuit