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Rupert

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Having replaced a single socket with a double and added a second double in the same room by extending the ring, by chance I found that there was no continuity in what I assumed was a ring final circuit. Checked my connections and all were good.

Just in case I was looking at a spur on spur connection rather than a ring I did some checks from the consumer unit.

The consumer unit has an RCBO on each circuit and all “sockets” are on one RCBO rated at 32A with two 2.5mm T+E cables connected. I disconnected both the live connectors and the neutral connectors then did a continuity test L to L and N to N and there was no continuity. So do I have an open ring circuit or two radials (which shouldn’t be on a 32A RCBO).

All sockets are live when the cables are connected but if I remove one cable all kitchen sockets are live plus 2 in a bedroom. Swapping the cables over brings on the other sockets.

The other surprising thing was that when testing between L and N on one of the cables there was around a 9 ohm path. This is on the circuit feeding the kitchen so unplugged what I could with no effect. I have to assume that this is a piece of circuitry in something that presents a low resistance to a low voltage DC test voltage but not to AC mains (otherwise I would be looking at a standing circuit current of 26+ amps assuming 240V).

Does anyone have any idea what sort of device might exhibit this performance when tested with DC.

Once I can isolate the cause of this I plan to link L+N of each cable independently at the consumer unit then test the loop resistance at each outlet hoping that the socket with the highest reading is the nearest to the end/break. Having done that on one cable I will do the same on the other cable and see where that gets me.

I checked in a number of sockets to see if I could find any loose wires but no joy so far. A number only had a single cable connected though so it looks as if there are a number of spurs !!

This is in a 1980 house that my daughter purchased a few months ago and I wasn’t too happy with some of the wiring I saw and in fact found a socket without an earth and another with a L-N reversal. She did have an electrician come and check things out as I wasn’t happy that everything was on this one “ring” including the oven. However the guy said it wasn’t unusual and as she had raised the issue she was aware of not turning too many things on at once !

Sorry its such a long post but i wanted to cover as much as possible up front, any advise on how to tackle this issue would be much appreciated.

Thanks
Graham
 
Having replaced a single socket with a double and added a second double in the same room by extending the ring, by chance I found that there was no continuity in what I assumed was a ring final circuit. Checked my connections and all were good.

Just in case I was looking at a spur on spur connection rather than a ring I did some checks from the consumer unit.

The consumer unit has an RCBO on each circuit and all “sockets” are on one RCBO rated at 32A with two 2.5mm T+E cables connected. I disconnected both the live connectors and the neutral connectors then did a continuity test L to L and N to N and there was no continuity. So do I have an open ring circuit or two radials (which shouldn’t be on a 32A RCBO).

All sockets are live when the cables are connected but if I remove one cable all kitchen sockets are live plus 2 in a bedroom. Swapping the cables over brings on the other sockets.

The other surprising thing was that when testing between L and N on one of the cables there was around a 9 ohm path. This is on the circuit feeding the kitchen so unplugged what I could with no effect. I have to assume that this is a piece of circuitry in something that presents a low resistance to a low voltage DC test voltage but not to AC mains (otherwise I would be looking at a standing circuit current of 26+ amps assuming 240V).

Does anyone have any idea what sort of device might exhibit this performance when tested with DC.

Once I can isolate the cause of this I plan to link L+N of each cable independently at the consumer unit then test the loop resistance at each outlet hoping that the socket with the highest reading is the nearest to the end/break. Having done that on one cable I will do the same on the other cable and see where that gets me.

I checked in a number of sockets to see if I could find any loose wires but no joy so far. A number only had a single cable connected though so it looks as if there are a number of spurs !!

This is in a 1980 house that my daughter purchased a few months ago and I wasn’t too happy with some of the wiring I saw and in fact found a socket without an earth and another with a L-N reversal. She did have an electrician come and check things out as I wasn’t happy that everything was on this one “ring” including the oven. However the guy said it wasn’t unusual and as she had raised the issue she was aware of not turning too many things on at once !

Sorry its such a long post but i wanted to cover as much as possible up front, any advise on how to tackle this issue would be much appreciated.

Thanks
Graham
Best to call in an Electrician Mate.
 
Did you check to see if it was a ring before your alterations?
 
There is probley a load of junction boxes under the floors aswell sound like there has been various alterations carried out , the sockets may never of been on ring or due to the alterations the ring as been brocken. As for the resistance between live and neutal is ther an emersion heater on the circuit ?
 
There is probley a load of junction boxes under the floors aswell sound like there has been various alterations carried out , the sockets may never of been on ring or due to the alterations the ring as been brocken. As for the resistance between live and neutal is ther an emersion heater on the circuit ?
No Immersion heater. The only things I have not been able to isolate so far are an inbuilt oven and a microwave oven.
 
Does anyone have any idea what sort of device might exhibit this performance when tested with DC.

Anything with a wirewound transformer or induction motor. Due to their inductance, these have AC impedances much higher than their DC resistance, so your resistance measurement won't tell you much about the AC load they present.

A perfect motor or transformer would have zero DC resistance, as the resistance only causes loss of energy as heat. Superconducting wire is not yet practical for domestic appliances though, so we have to make do with good old copper, and put up with its unavoidable resistivity.
 
So this electrician who came to check things out wasn't much help, then? Unless you get someone in who knows what to do you're going to be going round in circles.
Suggest a full EICR.....by a fully qualified electrician.
 
I thought that was what she was going to get but it turns out the guy that came said he wasn't qualified to give a report or do Part P stuff.
If I can't find out what's going on I will get an engineer in for her but I have an engineering background and like a challenge.
 
To start fair play for doing some testing in the first place if your not a spark as very few would. Sounds a bit strange but nearly impossible to tell without being there if it's a damaged ring or 2 radials. Has anywhere in the house had anything done recently? Also why did the original spark not pick up on this what did he do
 
My daughter needed the Hob switch moved and a couple of single sockets changed to doubles so she got an electrician in to do the work. As I had previously voiced my concern that all sockets, the oven, microwave, tumble dryer, washing machine and dishwasher were all on this one RCBO I suggested that she ask the electrician if that was OK. As I said in my previous post he said it wasn't unusual but as she was aware of the issue just to not use too many things at the same time. If she did he said the circuit would just trip.
I asked her if he had done a full test and she said not as he wasn't certified to do it !
I have subsequently checked what he had did but it is electrically sound.
I do all my own electrical work, under BCO where necessary and feel comfortable to continue with the troubleshooting. As all recent work doesn't seem to have caused the problem it may be historical. I can't believe that someone ran two radials on 2.5mm on a 32A RCBO.

I doubt this is the original Consumer Unit given that all circuits have RCBO's so there probably has been an upgrade at some time also a few years ago the kitchen was up dated. It was in the kitchen that I had originally found a L-N reversal and another socket with a disconnected earth.
I just wondered as professionals how you would approach the troubleshooting so if nothing else I can take some of the leg work out of the job before we call a registered electrician.
 
Rupert, as you 1st post.join L and E of 1 legin the CU.measurer R1+R2 at each socket. ( only those on that leg will five a reading ) . mark each socket with a wipeavle felt pn with its reading. repeat for other leg. then you can map out the circuit and see where the break, if any, is. options are then to either:
1. reinstate ring, if practicable.
2.convert to 2 x 20A radials.

2.5mm T/E will have a reading of approx 0.02 ohms/meter. (remember to null leads beforehand.).
 
Rupert, as you 1st post.join L and E of 1 legin the CU.measurer R1+R2 at each socket. ( only those on that leg will five a reading ) . mark each socket with a wipeavle felt pn with its reading. repeat for other leg. then you can map out the circuit and see where the break, if any, is. options are then to either:
1. reinstate ring, if practicable.
2.convert to 2 x 20A radials.

2.5mm T/E will have a reading of approx 0.02 ohms/meter. (remember to null leads beforehand.).

Thanks for that telectrix that's along the lines of what I was thinking.
The 0.02 ohms that you quote is that R1+R2 ?
Can you point me to a Low Resistance Reading Ohm meter as mine has only 0.1 accuracy and I had noted that when checking for a bridge I would be looking for readings within 0.05 Ohms
 
Rupert, as you 1st post.join L and E of 1 legin the CU.measurer R1+R2 at each socket. ( only those on that leg will five a reading ) . mark each socket with a wipeavle felt pn with its reading. repeat for other leg. then you can map out the circuit and see where the break, if any, is. options are then to either:
1. reinstate ring, if practicable.
2.convert to 2 x 20A radials.

2.5mm T/E will have a reading of approx 0.02 ohms/meter. (remember to null leads beforehand.).

Thanks for that telectrix that's along the lines of what I was thinking.
The 0.02 ohms that you quote is that R1+R2 ?
Can you point me to a Low Resistance Reading Ohm meter as mine has only 0.1 accuracy and I had noted that when checking for a bridge I would be looking for readings within 0.05 Ohms
 
most MFT swill read to 2 dec. places. (0.01).i have a low ohms meter that reads to 3. i.e. 0.001 ohms.

if you extrapolate that's 0.1 ohms / 5 metres.
 

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