Continuity / Ohms testing help / Short ?

[king185]

Hi,

I would love some help understanding an issue I’m having on a 16mm SWA cable running from the CU in my house to the CU in the shed.
I believe there is a problem with the cable (possibly between E and N), and I have used a multi-meter to do some checks on the CU (shed side) and below you will see my finding.
Please note that the tests are done whilst the MCB in the house is OFF so there is no voltage at the shed whilst performing these tests, however the cables are still connected at the CU in the house (shed ones are disconnected).


https://1drv.ms/i/s!AicNdL7JWhGahawkCq1gV5yjwZM3uA?e=UoM1WT
https://1drv.ms/i/s!AicNdL7JWhGahawj2CAfR9zxn-Pi5g?e=Obqlme
I think my electric supply coming into my house is TN-S. I will attach a 2 photos above so someone might be able to confirm this.
Also to note i did a continuity test between the earth bar and the neutral bar in my CU in the house and we have a LOUD BEEP.


https://1drv.ms/i/s!AicNdL7JWhGahawcNYe4hV-GacO3cA?e=2mzlCy
Above is common (black cable from multi-meter) connected to N and red cable connected to E.
Multi-meter is in AUTO MODE set to OHMS and we get 2.1 ohms.


https://1drv.ms/i/s!AicNdL7JWhGahawWWt91uVD49sVKiA?e=w6s24B
Above is common (black cable from multi-meter) connected to N and red cable connected to E.
Multi-meter is in IN MANUAL MODE set to OHMS and we get 3.9 ohms.


https://1drv.ms/i/s!AicNdL7JWhGahawbWsXbg4qcmA6VaA?e=ZHEvAA
Above is common (black cable from multi-meter) connected to N and red cable connected to E.
Multi-meter is in CONTINUITY MODE and we get a LOUD BEEP with a reading of 7.9 (is this ohms?) – I do not know what this means.
But I do understand that there is a pathway between N and E which seems like that maybe the fault.


https://1drv.ms/i/s!AicNdL7JWhGahawU1iw4AK0u4_8v0w?e=Tt1fWV
Above is common (black cable from multi-meter) connected to E and red cable connected to N (notice I switched the cables around to see if it makes a difference).
Multi-meter is in IN MANUAL MODE set to OHMS and we get 0.0 ohms
This occurs again even in AUTO MODE (no photo for this) for ohms it gives a straight 0.00 instead of OPEN LINE.
I find this strange, but I don’t know why. Haha.


https://1drv.ms/i/s!AicNdL7JWhGahawS2aPPBwa4Fi_ynA?e=PRyDnv
Above is common (black cable from multi-meter) connected to E and red cable connected to N (notice I switched the cables around to see if it makes a difference).
Multi-meter is in CONTINUITY MODE and we get a LOUD BEEP AGAIN with a reading of 4.5 (is this ohms?) – AGAIN I do not know what this means. But I think something is wrong.


https://1drv.ms/i/s!AicNdL7JWhGahawZYfAcD4saxhHRFg?e=I0nULJ
Above is common (black cable from multi-meter) connected to N and red cable connected to L.
Multi-meter is in AUTO MODE set to OHMS and we get 5.063 M ohms.
I think this is MEGA ohms and I don’t understand if this is normal, I think this is normal.


https://1drv.ms/i/s!AicNdL7JWhGahawY10VSgWlnTrBv2A?e=YIOnj9
Above is common (black cable from multi-meter) connected to N and red cable connected to L.
Multi-meter is in IN MANUAL MODE set to OHMS and we get OPEN LINE.
I don’t understand why there is a difference between AUTO MODE showing over 5 MEGA ohms and this manual mode showing OPEN LINE, but I think this is GOOD and normal.


https://1drv.ms/i/s!AicNdL7JWhGahawaIPdmInzCpcFK1g?e=SGCVQc
Above is common (black cable from multi-meter) connected to N and red cable connected to L.
Multi-meter is in CONTINUITY MODE and we get a NO BEEP with a reading of OPEN LINE.
This looks OK to me.


https://1drv.ms/i/s!AicNdL7JWhGahawXMPHXIuM7a3eoDg?e=H2dJy1
Above is common (black cable from multi-meter) connected to E and red cable connected to L.
Multi-meter is in AUTO MODE set to OHMS and we get 5.99 M ohms.
Again I am not sure if this is normal.


https://1drv.ms/i/s!AicNdL7JWhGahawTQTuFMqUuID58Hg?e=D68YO2
Above is common (black cable from multi-meter) connected to E and red cable connected to L.
Multi-meter is in IN MANUAL MODE set to OHMS and we get OPEN LINE.
I think this is GOOD.


https://1drv.ms/i/s!AicNdL7JWhGahawVl-ZTh4bCmK7H8A?e=XHN1Mq
Above is common (black cable from multi-meter) connected to E and red cable connected to L.
Multi-meter is in CONTINUITY MODE and we get a NO BEEP with a reading of OPEN LINE.
This looks OK to me.



Does anyone have any thoughts as to what is going on?
Do you think I should do further tests or is it simple to say there is a NEUTRAL to EARTH fault on my 16mm2 SWA cable?

Help will be much appreciated.

Kind regards.

 

[Andy™]

well since TNS is linked N-E you are going to get a N-E 'fault' if you don't disconnect it and test properly... id say you've spent a lot of time wasted doing nothing productive since you haven't isolated the cable...

to test a cable properly you are need an insulation resistance tester. a multimeter is not suitable

and more importantly, why are you doing all this anyway?

 

[Murdoch]

The quickest way to isolate the N from the E is to turn off the main switch OR the RCD protecting the MCB

Who installed the cable and why is it 16mm ?

 

[poni]

if you only switched off the MCB then you left the earth and Neutral connected in the house Consumer Unit that is why you are getting a low resistance between black and green and yellow this is an AC circuit so you don't need to swap the leads around

 

[SPECIAL LOCATION]

Does anyone have any thoughts as to what is going on?
Do you think I should do further tests or is it simple to say there is a NEUTRAL to EARTH fault on my 16mm2 SWA cable?

Help will be much appreciated.

Kind regards.

Impossible to conclude anything from the information given..
And you have made no mention of the reason(s) why you think the 16mm SWA is faulty?

I think you need to prove continuity of all conductors.. R1, R2, Rn and the armour.
Then confirm insulation resistance between all conductors, and armour, before you could even hazard a guess if there are any issues with the SWA.?

I think you also need a calibrated test meter that can zero the leads, before attempting any continuity measurements.

Random guess work testing, without any idea of what results you should expect is just a waste of time in my opinion.

 

[king185]

I would like to add some more information here.

I missed some important points. I apologise.

I understand its probably not an E - N fault as i think my supply in my house is TN-S.

The SWA cable is 2 core only L and N with the steel cable around acting as an E.
All the tests ive conducted to earth is to the outer steel cabling.

This 16mm cable was there when the house was bought and runs from the house to the shed and powers another CU in the shed.

The reason for this investigation is that the MCB (running the SWA cable) in the house keeps tripping usually slowly anywhere between 5 mins to 2 hours but sometimes immediately.
Nothing in the shed is faulty this has been tested throughly and each induvidual MCB in the shed has been disconnected.
It all boils down to this cable as the tripping of the MCB in the house still occurs even when the cable (shed end) has nothing attached.

The CU in the house does not have ANY RCD protection. It is an old CU which will be updated in the near future.

I will perform all the tests after the cable has been disconnected from the CU in the house and in the shed. So i will simply be testing a cable that has no connections on either ends.

The multi-meter has a feature where i can zero the leads, before attempting any continuity measurements. This can be done.

If the resistance cannot be tested correctly with this multimeter an insulation resistance tester can be used to check at a later date. But please double confirm this is the case.

OBJECTIVE:

Test the cable correctly.

Dig it out of the ground.

Inspect it all the way along. (this has been mostly done where i can access the cable). There are signs of damage which have been fixed however not all the cable is accessible as some of it goes underground into concrete.

Get a hack saw and cut it where it makes sense. Saving as much cable as possible as its very expensiver per meter.

Perform the same tests to make sure cable going to the house is good.

Cut it again and perform the same tests to make sure cable going to the shed is good.

Get 2 resin underground SWA cable joint kits.

Bury the cable.

My apologies if some tests were not conducted properly. Im learning alot already.

Thank you

 

[Andy™]

id expect it would be cheaper and far easier to pay for a sparky to test the cable using the correct equipment than it will be to dig it up and 'inspect' it

and since you've only turned off MCB's in the shed, you haven't elminated any fault in the shed so you've wasted your time there again

if its a contant issue of RCD tripping then id expect many electricians would be able to find some indication of the fault and which circuit in less than an hour. if its intermittant then it does complicate things as a fault may not always show up even with a proper test kit. your multimeter has no chance

 

[Murdoch]

Or a possible plan B

1. Test sub main under taken by competent spark.

2. If the sub main is faulty, replace from end to end as introducing additional connections will only by weak points.

 

[apprentice87]

Hi,

I would love some help understanding an issue I’m having on a 16mm SWA cable running from the CU in my house to the CU in the shed.
I believe there is a problem with the cable (possibly between E and N), and I have used a multi-meter to do some checks on the CU (shed side) and below you will see my finding.
Please note that the tests are done whilst the MCB in the house is OFF so there is no voltage at the shed whilst performing these tests, however the cables are still connected at the CU in the house (shed ones are disconnected).


https://1drv.ms/i/s!AicNdL7JWhGahawkCq1gV5yjwZM3uA?e=UoM1WT
https://1drv.ms/i/s!AicNdL7JWhGahawj2CAfR9zxn-Pi5g?e=Obqlme
I think my electric supply coming into my house is TN-S. I will attach a 2 photos above so someone might be able to confirm this.
Also to note i did a continuity test between the earth bar and the neutral bar in my CU in the house and we have a LOUD BEEP.


https://1drv.ms/i/s!AicNdL7JWhGahawcNYe4hV-GacO3cA?e=2mzlCy
Above is common (black cable from multi-meter) connected to N and red cable connected to E.
Multi-meter is in AUTO MODE set to OHMS and we get 2.1 ohms.


https://1drv.ms/i/s!AicNdL7JWhGahawWWt91uVD49sVKiA?e=w6s24B
Above is common (black cable from multi-meter) connected to N and red cable connected to E.
Multi-meter is in IN MANUAL MODE set to OHMS and we get 3.9 ohms.


https://1drv.ms/i/s!AicNdL7JWhGahawbWsXbg4qcmA6VaA?e=ZHEvAA
Above is common (black cable from multi-meter) connected to N and red cable connected to E.
Multi-meter is in CONTINUITY MODE and we get a LOUD BEEP with a reading of 7.9 (is this ohms?) – I do not know what this means.
But I do understand that there is a pathway between N and E which seems like that maybe the fault.


https://1drv.ms/i/s!AicNdL7JWhGahawU1iw4AK0u4_8v0w?e=Tt1fWV
Above is common (black cable from multi-meter) connected to E and red cable connected to N (notice I switched the cables around to see if it makes a difference).
Multi-meter is in IN MANUAL MODE set to OHMS and we get 0.0 ohms
This occurs again even in AUTO MODE (no photo for this) for ohms it gives a straight 0.00 instead of OPEN LINE.
I find this strange, but I don’t know why. Haha.


https://1drv.ms/i/s!AicNdL7JWhGahawS2aPPBwa4Fi_ynA?e=PRyDnv
Above is common (black cable from multi-meter) connected to E and red cable connected to N (notice I switched the cables around to see if it makes a difference).
Multi-meter is in CONTINUITY MODE and we get a LOUD BEEP AGAIN with a reading of 4.5 (is this ohms?) – AGAIN I do not know what this means. But I think something is wrong.


https://1drv.ms/i/s!AicNdL7JWhGahawZYfAcD4saxhHRFg?e=I0nULJ
Above is common (black cable from multi-meter) connected to N and red cable connected to L.
Multi-meter is in AUTO MODE set to OHMS and we get 5.063 M ohms.
I think this is MEGA ohms and I don’t understand if this is normal, I think this is normal.


https://1drv.ms/i/s!AicNdL7JWhGahawY10VSgWlnTrBv2A?e=YIOnj9
Above is common (black cable from multi-meter) connected to N and red cable connected to L.
Multi-meter is in IN MANUAL MODE set to OHMS and we get OPEN LINE.
I don’t understand why there is a difference between AUTO MODE showing over 5 MEGA ohms and this manual mode showing OPEN LINE, but I think this is GOOD and normal.


https://1drv.ms/i/s!AicNdL7JWhGahawaIPdmInzCpcFK1g?e=SGCVQc
Above is common (black cable from multi-meter) connected to N and red cable connected to L.
Multi-meter is in CONTINUITY MODE and we get a NO BEEP with a reading of OPEN LINE.
This looks OK to me.


https://1drv.ms/i/s!AicNdL7JWhGahawXMPHXIuM7a3eoDg?e=H2dJy1
Above is common (black cable from multi-meter) connected to E and red cable connected to L.
Multi-meter is in AUTO MODE set to OHMS and we get 5.99 M ohms.
Again I am not sure if this is normal.


https://1drv.ms/i/s!AicNdL7JWhGahawTQTuFMqUuID58Hg?e=D68YO2
Above is common (black cable from multi-meter) connected to E and red cable connected to L.
Multi-meter is in IN MANUAL MODE set to OHMS and we get OPEN LINE.
I think this is GOOD.


https://1drv.ms/i/s!AicNdL7JWhGahawVl-ZTh4bCmK7H8A?e=XHN1Mq
Above is common (black cable from multi-meter) connected to E and red cable connected to L.
Multi-meter is in CONTINUITY MODE and we get a NO BEEP with a reading of OPEN LINE.
This looks OK to me.



Does anyone have any thoughts as to what is going on?
Do you think I should do further tests or is it simple to say there is a NEUTRAL to EARTH fault on my 16mm2 SWA cable?

Help will be much appreciated.

Kind regards.

You are completely wasting your time... As for digging the cable up, that would be barmy. Trying to joint it, would be even worse.

Just disconnect it both ends and test it with a proper insulation tester, anything else and you are not going to get anywhere. Might i suggest getting an electrician to test the cable is going to be a lot cheaper than buying an insulation tester.

Might i suggest that if you DO want to buy one, post it on here first so we can tell you if it is suitable..

john..

 

[kerching]

Sorry but you have completely wasted your time

Why did you think there was a fault in the first place?

 

[Murdoch]

Why did you think there was a fault in the first place?

OP says it trips randomly

My money is on an old damaged cable - damage by spade or tree trunk

 

[binky]

OP says it trips randomly

My money is on an old damaged cable - damage by spade or tree trunk

Spiders in fittings or other small annoying wildlife.

 

[kerching]

@Murdoch hanks for that. I'd lost the will after a while
My money is on ants or slugs .
Needs meggering or a "thumper"

 

[Murdoch]

A photo of the house CU would be helpful

 

[king185]

Ok thank you all for answering

I will repeat that the house CU has no RCD protection so there is no RCD tripping, as thats impossible.
As for the shed nothing trips there as in no circuits.
So not using the multi-meter to find faults that dont exsist

There is no fault in the circuits in the shed.

The fault clearly lies in the SWA cable. I say this because the MCB in the house constantly trips even when the CU is disconnected and removed in the shed.

The MCB that trips in the house has the cable that runs to the shed attached to nothing.

This MCB was already replaced and it did not fix the issue. Not a faulty MCB.

Also just to mention the 16mm SWA cable that runs from the house to the shed is around 55 to 65 meters in length. Its long!

It is possible the cable was damaged somewhere due to foundation of a fence. Either way it cannot all be removed from the ground as some of it goes under the concrete foudations of my neighbours fence.

The middle or some section of the cable will but cut out and replaced, but of course i will get a sparky to look and test with an insulation resistance tester so we know where to cut in order to save as much cable as possible as its expensive!

Thank you all for the help.


https://1drv.ms/i/s!AicNdL7JWhGaha5vj9GjThJPJyp-ZQ?e=lTcdpH
https://1drv.ms/i/s!AicNdL7JWhGaha5wgCWO5_XMwD2-ZA?e=pSjhNw
Above are photos of my house CU

 

[Murdoch]

Thanks for the additional information. Useful to get more facts.

Bear in mind it may take several cuts to identify the damaged section!

 

[kerching]

It should be an easy fault to find if you can find someon with a TDR( time domain reflectometer)
Otherwise it's going to be 'halve,cut,test,halve again, test again, joint,repeat'.....and expensive

 

[apprentice87]

Ok thank you all for answering

I will repeat that the house CU has no RCD protection so there is no RCD tripping, as thats impossible.
As for the shed nothing trips there as in no circuits.
So not using the multi-meter to find faults that dont exsist

There is no fault in the circuits in the shed.

The fault clearly lies in the SWA cable. I say this because the MCB in the house constantly trips even when the CU is disconnected and removed in the shed.

The MCB that trips in the house has the cable that runs to the shed attached to nothing.

This MCB was already replaced and it did not fix the issue. Not a faulty MCB.

Also just to mention the 16mm SWA cable that runs from the house to the shed is around 55 to 65 meters in length. Its long!

It is possible the cable was damaged somewhere due to foundation of a fence. Either way it cannot all be removed from the ground as some of it goes under the concrete foudations of my neighbours fence.

The middle or some section of the cable will but cut out and replaced, but of course i will get a sparky to look and test with an insulation resistance tester so we know where to cut in order to save as much cable as possible as its expensive!

Thank you all for the help.


https://1drv.ms/i/s!AicNdL7JWhGaha5vj9GjThJPJyp-ZQ?e=lTcdpH
https://1drv.ms/i/s!AicNdL7JWhGaha5wgCWO5_XMwD2-ZA?e=pSjhNw
Above are photos of my house CU

Can i give you some advice?? You will never find the fault...

1, as said, you are wasting your time with a multimeter, what voltage does it use to test?? about 2 volts or something. An insulation tester, mine goes up to 1000v. entirely different. With one of these, you "might" find the fault is there all the time.

2, Next problem, you are planning on cutting sections to test. Where this will go wrong, is that the fault is intermittant, so you will be cutting out sections and probably finding nothing..

3, By the time you do all this, you will most likely find that it was cheaper just to have replaced the cable at a cost of about £360...

john..

 

[binky]

Ok thank you all for answering

I will repeat that the house CU has no RCD protection so there is no RCD tripping, as thats impossible.
As for the shed nothing trips there as in no circuits.
So not using the multi-meter to find faults that dont exsist

There is no fault in the circuits in the shed.

The fault clearly lies in the SWA cable. I say this because the MCB in the house constantly trips even when the CU is disconnected and removed in the shed.



The middle or some section of the cable will but cut out and replaced, but of course i will get a sparky to look and test with an insulation resistance tester so we know where to cut in order to save as much cable as possible as its expensive!

Thank you all for the help.

I take it it was all working fine before the fence went in?

 

[kerching]

Even when you find the fault there may be 'good' sections that have been fault stressed and fail further down the line. If I was doing this I would advise to swap it. Take out whatever cable,is accessible, strip it and weight it in for scrap!