DIY Trainees Question Only????

[Paul.M]

This is from the DIY section of the forum and I think it is a good fault find for you guys to have a go at in here. Mentors please dont tell them, promt but dont tell


Hi all,

I've just removed all the upstairs sockets ( mk plastic type ) and replaced them with brushed stainless sockets. I have earthed them and also earthed them to the back box, I've also checked all wires are tight and good but the mcb keeps tripping out? It has only started doing this since I put these new sockets on. Any help much appreciated!

 

[Loki]

I would most likely suspect they have pinched the neutral to the earthed metal back box or by the faceplate screw when fitting the faceplate creating a neutral to earth fault?

Or that they have incorrectly wired a socket (or two).


Michael

 

[telectrix]

loki. hint..... it's the MCB that's tripping.

 

[Loki]

loki. hint..... it's the MCB that's tripping.

Hmm Ok then, like as I said before but a live to earth fault?
Also is their anything plugged in the sockets? could be a faulty appliance? but then that would have also happened on the old MK sockets


Michael

 

[Pete999]

Hmm Ok then, like as I said before but a live to earth fault?
Also is their anything plugged in the sockets? could be a faulty appliance?


Michael

To much of a coincidence I would think, but explore all the options. A series of tests would confirm what the problem is wouldn't it?

 

[Loki]

To much of a coincidence I would think, but explore all the options. A series of tests would confirm what the problem is wouldn't it?

I start my apprenticeship on the 9th March so don't know the correct testing procedures yet but if the MCB does not trip straightaway then I would first try a Kewtech 103 socket tester on each socket that was fitted. I know this does not check a reversed Neutral Earth but would pick up incorrect wiring. This would save powering down the consumer board & running continuity tests on the live - live, neutral - neutral & earth - earth. If you did safely power down the consumer unit I would test continuity between live, neutral & earth on that ring.

Michael

 

[Bobster]

Nice try, but a socket tester wouldn't proove anything in this situation.

I realise you're just starting out, have a read up on insulation testing.

Any questions on these type of tests just shout up.

 

[Loki]

Nice try, but a socket tester wouldn't proove anything in this situation.

I realise you're just starting out, have a read up on insulation testing.

Any questions on these type of tests just shout up.

Hi Rob,

Thanks for your offer of help, I will defiantly take you up on that .

From what I've researched already & this video ( & the one that follows on afterwards) https://www.youtube.com/watch?v=YjFmfRzb8SM
Doesn't an insulation test just make sure that their is no shorts/leakage on that circuit between live & earth, live & neutral, earth & neutral, Neutral & earth ie 500v >299 mΩ

Michael

 

[cotty]

Reverse Polarity? Just a thought!

 

[Loki]

Reverse Polarity? Just a thought!

So let me see if I understand this right. A Kewtech 103 does check reverse polarity as long as the MCB doesn't trip but in this case it did in the original question so cant be used this time.
Safe isolation of the consumer unit & testing continuity between live, neutral & earth also wouldnt work as their is no shorting. Insulation resistance testing would also come back as ok ie >299 mΩ
So a visual inspection of each socket wiring would pick this up.
Also Kewtech R2 tester in the socket & a wander lead to the MFT at the CU & a resistance/continuity test would also work ie test live in plug & brown wire at CU if ok then test neutral & earth the same way. When you come to a socket where the brown wire at CU went to neutral in the socket this would be the issue.


Michael

 

[kevio123]

It wouldn't be reverse polarity as it would still work if wired the wrong way round.. Just extremely dangerous.. Is the problem the double earth? Surely the earth to the consumer unit is all that's needed? I'd switch power off and give the sockets a visual inspection to make sure the conductors are secure.. Then do a continuity of ring circuit test.

 

[Pete999]

Nice try, but a socket tester wouldn't proove anything in this situation.

I realise you're just starting out, have a read up on insulation testing.

Any questions on these type of tests just shout up.

What Rob said

 

[Simonslimline]

It wouldn't be reverse polarity as it would still work if wired the wrong way round.. Just extremely dangerous.. Is the problem the double earth? Surely the earth to the consumer unit is all that's needed? I'd switch power off and give the sockets a visual inspection to make sure the conductors are secure.. Then do a continuity of ring circuit test.

Have a read of Guidance Note 8 if possible, (9.7 Terminations & accessories).

 

[Pete999]

I would still recommend that you do an IR test, r1,r2,rn and an R1+R2 test on the circuit concerned with the circuit completely disconnected from the CU, these tests will prove the following the IR is OK, the circuit conductors have continuity and the RFC is actually a RFC, do these tests and come back with the results. https://www.youtube.com/results?search_query=ring+main+testing

 

[Simonslimline]

The MCB will operate under Short circuit, overload & Line/earth fault.

The fault Must be either a SC or Line/earth fault if the PD is operating instantaneously. Assuming the circuit is not protected by an RCD then it could be either of these faults.

If the DIY'er is mistaking An RCD for an MCB as written then it could be down to a Line/earth or Neutral earth Fault and not a Short circuit.


I would do a visual check at each socket first, if failing to spot any problems then a continuity test followed by an insulation resistance test.

This should flag up the issue.

 

[pennychew]

They must have put the wiires back in the wrong terminals on at least one of the sockets, maybe the upstairs ring has new and old colour wiring to confuse them a bit more! I'd do a visual of the sockets connections first as well

 

[Jamie]

Unplug anything in that socket circuit (if anything), buzz or insulation test between L-E/L-N

If it is not clear (probably won't be), disconnect one leg of the circuit at C/U and break the ring at a mid-way point in the socket ring, so the ends are disconnected and in theory makes two radial circuits.

Energize one leg (obviously the open ends at the socket would be terminated separately so they aren't just hanging), if it pops off then you know it's on that energized leg, then try the other leg and see which sockets are on with plug in tester . Start unscrewing ones that are not energized and visual inspection for incorrect termination/squashed cables/nicked cables etc etc

That is how i did a fault the other week with socket rcbo keep tripping, find offending socket and turned out to be L-E as live was poorly terminated (a lot of copper showing outside of terminal) and touching the metal back box causing it to trip off.

 

[Paul.M]

Please dont try to find a fault by energizing the circuit. This fault can be found by dead testing and you pretty much explained it Jamie.


What do you all think about this DIY question, would you like to see more of this type of thread?

 

[pennychew]

Please dont try to find a fault by energizing the circuit. This fault can be found by dead testing and you pretty much explained it Jamie.


What do you all think about this DIY question, would you like to see more of this type of thread?

Definitely would, gets you thinking and a good way to learn some fault finding techniques

 

[Paul.M]

I'm looking through the DIY section to find an appropriate thread. If any other Mentor sees one, give me a shout.