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When I use Alphatek, the RCD trip times can be very different with stuff plugged in.
Dead Testing
- Thread starter Iggifer
- Start date
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There was very little stuff plugged in, as I didn't go round after testing earlier and plug everything back in, just what I'm using - computer & it's friends, phone + router, and that's about it.
Will double check my results when everything's unplugged tomorrow
Will double check my results when everything's unplugged tomorrow
Then your instructor needs to go back to college.
One of the basic lessons you first learn is not to touch the probe tips. If testing resistance you will get spurious results due to your body resistance interfering with the result.
If testing for voltage you will get a belt! Bare tips should only project 1-2mm from the insulated probes to prevent you touching them and getting a lethal shock and also prevent 'arcing' between terminals if they slip.
Sorry I didn't describe the technique very well. Holding the probe with your 4 fingers beyond the finger guard and then pressing the cable from the insulation onto the probe tip. This also works with the shrouded GS38 tips and the switched probe
There's no touching of probe tips / copper and obviously you would never use this technique for live or IR testing. Dead only.
I'm not disputing that it may be bad technique - but if that's what you've been shown...
There's no touching of probe tips / copper and obviously you would never use this technique for live or IR testing. Dead only.
I'm not disputing that it may be bad technique - but if that's what you've been shown...
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I'm confused by this statement too - if anything it ought to lower the resistance. Some more things to check are there's no induced voltages messing up the testers readings, the connections and interlinks are sound and the batteries in the tester are good.
RCDs are meant to be tested in isolation I.e. nothing connected.
I'm beaten by this. I spoke to an electrician friend at length today and he couldn't offer much else.
I disconnected the ring entirely, to establish which leg went where, and there appear to be no bridges, it seems its a genuine RFC.
I think the plan is now, unless somebody can point me in a different direction, is to split it into 2 x 20a radials, one for leg 1 (red) and one for leg 2 (blue). I would be happier with this arrangement anyway.
Second Round Of Test Results
End To End
CPC - 0.84
L - 0.52
N - 0.53
Interconnect
L-N
1 - 0.35
2 - 0.32
3 - 0.33
4 - 0.34
5 - 0.36
6 - 0.32
7 - 0.34
8 - 0.39
9 - 0.34
10 - 0.59 (spur)
11 - 0.35
L-E
1 - 33.8
2 - 35.1
3 - 35.5
4 - 36.4
5 - 35.2
6 - 35.8
7 - 35.6
8 - 36.0
9 - 36.0
10 - 36.9
11 - 55.9 (Outside SKT, not spur)
This is leading me to believe there is a problem at the outside socket, as to what that problem is, not a clue.
I disconnected the ring entirely, to establish which leg went where, and there appear to be no bridges, it seems its a genuine RFC.
I think the plan is now, unless somebody can point me in a different direction, is to split it into 2 x 20a radials, one for leg 1 (red) and one for leg 2 (blue). I would be happier with this arrangement anyway.
Second Round Of Test Results
End To End
CPC - 0.84
L - 0.52
N - 0.53
Interconnect
L-N
1 - 0.35
2 - 0.32
3 - 0.33
4 - 0.34
5 - 0.36
6 - 0.32
7 - 0.34
8 - 0.39
9 - 0.34
10 - 0.59 (spur)
11 - 0.35
L-E
1 - 33.8
2 - 35.1
3 - 35.5
4 - 36.4
5 - 35.2
6 - 35.8
7 - 35.6
8 - 36.0
9 - 36.0
10 - 36.9
11 - 55.9 (Outside SKT, not spur)
This is leading me to believe there is a problem at the outside socket, as to what that problem is, not a clue.
If you have (intend to) split the ring into two radials WHY are you bothering to show the second batch of ring final test results - aren't they the same as the first round.
As I suggested earlier treat each leg as a radial and test accordingly.
What should you expect as you move away from the consumer unit
from your R1+R2 results?
They're the ones that should give you clues to what the problem is - take them and put them up here.
As I suggested earlier treat each leg as a radial and test accordingly.
What should you expect as you move away from the consumer unit
from your R1+R2 results?
They're the ones that should give you clues to what the problem is - take them and put them up here.
Splitting it into 2 radials is an option, not something I am settled on just yet, I would like to resolve the existing fault rather than just ignoring it by splitting.
Second round of test results were to confirm I hadn't done something silly yesterday. Today was more systematic too, same technique at every socket outlet etc
I only just finished establishing which leg supplied which side of the ring when I posted earlier. I obviously could have just broken the ring 'half way' but now I know exactly which socket joins the two legs, so can break it there tomorrow and get accurate results.
R1+R2 will increase as you move away from the CU on a radial, meaning outlets 2 & 6 will have the highest reading if I break at outlet 2.
Will do R1+R2 tomorrow am
Second round of test results were to confirm I hadn't done something silly yesterday. Today was more systematic too, same technique at every socket outlet etc
I only just finished establishing which leg supplied which side of the ring when I posted earlier. I obviously could have just broken the ring 'half way' but now I know exactly which socket joins the two legs, so can break it there tomorrow and get accurate results.
R1+R2 will increase as you move away from the CU on a radial, meaning outlets 2 & 6 will have the highest reading if I break at outlet 2.
Will do R1+R2 tomorrow am
By the way you are not spliting the ring final circuit into two 20Amp radials for testing you are just splitting the ring final circuit.
In other words pick a socket on the ring take out one set of conductors from the socket - leaving the others in place.
Back at the CU put the L and E together into a terminal block and test each socket.
If you immediately start to get the high readings at the first socket on the new radial then you should disconnect the outgoing cable from the socket and only have the CU side cable in place - conduct the test again.
If you still have a high reading, then just for sanity sake connect the outgoing L/E together in a terminal block and continue to test along the circuit - with any luck you should get a low ohm reading.
If you get low readings all the way along then you know the problem is on the other radial so start the same process again.
It is always possible that the socket itself is the problem.
or you have a faulty tester.
Or you are not using the tester properly. (Though you said you got good results on the other circuit.)
For fault finding you have to follow a systematic but logical approach and don't let the blighter beat you.
In other words pick a socket on the ring take out one set of conductors from the socket - leaving the others in place.
Back at the CU put the L and E together into a terminal block and test each socket.
If you immediately start to get the high readings at the first socket on the new radial then you should disconnect the outgoing cable from the socket and only have the CU side cable in place - conduct the test again.
If you still have a high reading, then just for sanity sake connect the outgoing L/E together in a terminal block and continue to test along the circuit - with any luck you should get a low ohm reading.
If you get low readings all the way along then you know the problem is on the other radial so start the same process again.
It is always possible that the socket itself is the problem.
or you have a faulty tester.
Or you are not using the tester properly. (Though you said you got good results on the other circuit.)
For fault finding you have to follow a systematic but logical approach and don't let the blighter beat you.
I don't have an answer, but -
Why has the r1+rn gone up from spot on 0.26 yesterday to 0.32-0.39 (excl. spur)?
There is nothing you can add to two conductors of 0.52 & 0.84 (jointly measured in parallel) to give a result of 33.8-36.9 (excl. o/s socket).
I'm a bit suspicious that the r1+r2 results are (exactly) one hundred times higher than they should be.
Does that help ???
Why has the r1+rn gone up from spot on 0.26 yesterday to 0.32-0.39 (excl. spur)?
There is nothing you can add to two conductors of 0.52 & 0.84 (jointly measured in parallel) to give a result of 33.8-36.9 (excl. o/s socket).
I'm a bit suspicious that the r1+r2 results are (exactly) one hundred times higher than they should be.
Does that help ???
There is no point splitting the RFC in to two radial circuits as there is still a high resistance somewhere and this will more than likely end up at one of the circuits.
You need to divide and conquer and follow the steps that riveralt has pointed out above.
Out of interest, have you taken a r1+r2 reading at the in/out-coming legs points at the CU, also have you taken any test with socket fronts off, testing across terminal points?
You need to divide and conquer and follow the steps that riveralt has pointed out above.
Out of interest, have you taken a r1+r2 reading at the in/out-coming legs points at the CU, also have you taken any test with socket fronts off, testing across terminal points?
I mean with my new consumer unit, split this ring into 2 x 20a radials. For functional use not for testing. Obviously I will try the splitting into two radials for testing purposes too.
Surely this would give me one socket as higher than the others / unless they're all faulty. I suspect the outside socket needs replacing.
The thought had crossed my mind, but this is the only test it's having problems with, All the other rings went fine. And have gone back to one and it's still fine.
quote="riveralt";p="2365140"]Or you are not using the tester properly[/quote]
Obviously a pretty high possibility. But mergers are pretty straightforward. Connecting L1 to CPC2 and L2 to CPC1 with connector blocks in the CU. Measuring resistance between live and cpc at the socket outlets. Test leads nulled, using socket tester and verified a couple of readings at the back of the socket outlets.
Possibly user error yesterday. I was much more thorough today than yesterday, and double / triple checked some results.
Very interesting thought. Not sure what it means though.
Not sure what the first part of that means, but yes I have confirmed across terminal points.
-----
It's the almost perfect end to end results that are confusing me. I can't see how L-E can be so high when the end to end's are basically perfect.
L - 0.52
N - 0.53
CPC - 0.84
0.53x1.67=0.89 ohms. Meaning the cpc is only 0.05 away from calculated for end to end, which is within tolerance. Just can't get my head around the massive difference & don't understand how it can happen. It's all about experience I guess
I mean't, where you have cross connected the two legs of r1 and r2.
Have you taken a reading at that point, across the two legs at the CU, as if it were a socket outlet?
Not end to end but cross connected!
Is there a design reason to do this because unless you or your electrician resolve the problem - the problem will still remain.
You will only gain experience by following the correct testing procedure in the correct order - rather than trying to guess what the problem might be.
No, but I will add that to the to-do list.
No, no real design reason to do this. Other than it's a fairly nice, easy way of splitting the ring that covers two rooms into two radials for a room each - a bit tidier.
Understood. At least once I solve it, I will have a better idea next time I come across it
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