Weird MCB trip

[JohnD]

...the wires behind the socket are chaffed, in fact I can see the wire in the Live cable as plastic covering is cut through.

it might be possible to fix this with heat-shrink sleeving, but I am not clear where the damage is. A photo would be extremely helpful //www.diynot.com/forums/viewtopic.php?t=129539

It has got to be fixed anyway.

If the insulation has been damaged scraping against the galvanised back-box, it will either trip the RCB or be quite dangerous.

 

[gbasl0]

Hi - yes I did suspect that and in previous post above someone already mentioned to check the extension, which i did and it does have an earth. In fact I plugged the fridge into the extension then the extension into the 'dodgy' socket and it tripped but the fridge via same extension works in another scoket on same circuit, also tried 3 different sockets. I'm puzzelled?!!

 

[gbasl0]

John D - I think you are right I am going to have to replace the wiring to the dodgy socket (still don't understand why the kettle and other appliances work in this socket without tripping?!) but the problem is socket is in a built in cupboard and wires then go under the floorboward the cupboard is built on.
When I get time I will unlink the socket from the other one I think it is wired into and then try and put a new cable in just to check.
Too busy watching Murray play now - cannot believe he is winning !

 

[JohnW2]

In fact I plugged the fridge into the extension then the extension into the 'dodgy' socket and it tripped but the fridge via same extension works in another scoket on same circuit...

Ah - I should have suggested that - a good way of ruling out the extension lead.

A thought has just occurred to me, which could explain what's going on. Maybe there is a fault in the fridge (causing a 'leak to earth', which should cause RCD tripping no matter which socket it's plugged in) but the so-called 'dodgy' socket is actually the only non-dodgy one on the circuit (maybe the 'first' one on the circuit) - in the sense of being the only one which has an effective earth (CPC) connection. If the other sockets didn't have effective earth connections, then the RCD wouldn't trip.

Do you by any chance have, or have access to, one of those much-frowned-upon plug-in socket testers? If you did, you should be able to find out if the other sockets had 'missing earths'.

Kind Regards, John.

 

[gbasl0]

John,
Thanks for the suggestion - that was a fear at the back of my mind. I was hoping it could not possibly be true as we have had an electrician test the whole house a few months back and it all passed! However I shall be investing in one of those plug in testers you mentioned just to be sure, if the other sockets are not properly earthed the electrician will get a piece of my mind and a demand for a refund!

 

[wingcoax]

If you can find him

 

[JohnW2]

John, Thanks for the suggestion - that was a fear at the back of my mind. I was hoping it could not possibly be true as we have had an electrician test the whole house a few months back and it all passed! However I shall be investing in one of those plug in testers you mentioned just to be sure, if the other sockets are not properly earthed the electrician will get a piece of my mind and a demand for a refund!

Even if that proved to be the case, before you point fingers too accusatively, don't forget that things may have changed (e.g. a connection working loose) since that testing.

If it were a 'radial' circuit (sockets simply connected in a row, with just one cable connecting the first one to CU), then what I suggested could easily happen - just one loose/broken earth connection would leave all 'downstream' sockets without an earth. However if, as is probably more likely, it is a 'ring' circuit (like a radial one, but with the last, as well as first, socket also connected back to the CU), there would have to be at least two faults to deprive any socket of its earth (since it should get earth connections via 'both directions') - so probably much less likely an occurrence.

I'll be interested to hear what you discover.

Kind Regards, John.

 

[gbasl0]

Interesting development.
I bought a circuit tester. Decided to go for a good one rather than cheap version. Bought a KewTech Loopcheck 107.

So the 'dodgy socket' gets an amber light on the earth, ie a faulty earth, so yes there is something worng with the socket.
The other sockets on the same circuit get a red light on the Loop test. Which apprently indicates an open circuit or swapped connections.

So I appear to have two faults, the open circuit (assume this means it is not a proper loop), and a faulty earth on the 'dodgy' socket.
I'm going to disconnect everything and start from basics connecting one socket at a time and trying to understand what is going on. Hoping it can be wired properly if I make the right connections as would be very difficult to rewire (partly concrete floor).

 

[JohnW2]

So the 'dodgy socket' gets an amber light on the earth, ie a faulty earth, so yes there is something worng with the socket. The other sockets on the same circuit get a red light on the Loop test. Which apprently indicates an open circuit or swapped connections.

As you say, very interesting - and obviously suggestive of at least one thing wrong with the circuit, perhaps more. Given that it is clearly far from a straightforward situation, I would be tempted to suggest that the time has probably come for you to get an electrician (and all the test gear which comes with him/her) on the case.

Kind Regards, John.

 

[martinxxxxxx]

You may still only have one fault. I find with the "plug in testers" some problem can have different indications on each socket - as yours does.

Personally I would isolate the circuit and do dead tests.

Please see what "Safe Isolation" means before doing this, for your own safety. it is in the WIKI section of this forum

Then removing all the wires from each socket "ring out" and IR test each leg of the circuit. This will give you an opportunity to map the circuit out too.

Sounds like a lot of work? Well in my experience, it is often quicker than poking around here and there. Plus every step you record you can know is only needing to be done once. As opposed to going round in circles.

Martin

 

[securespark]

As opposed to going round in circles.

Or not, if it's not a ring final circuit...!

 

[gbasl0]

Thanks Martin - that is exactly what I plan to do. I don't think it is too complicated and am more confident in my ability than I am in a number of 'qualified' electricians I have had for various jobs over the last few years. Will keep you posted on what I find - but will be a little while as I don't get much free time from job/wife/kids !

 

[JohnW2]

Thanks Martin - that is exactly what I plan to do. I don't think it is too complicated and am more confident in my ability than I am in a number of 'qualified' electricians I have had for various jobs over the last few years. Will keep you posted on what I find - but will be a little while as I don't get much free time from job/wife/kids !

Hi again ...how are you planning on doing the IR tests as suggested? - until a couiple of days ago, you didn't even have a plug-in tester and, has been said, they can often give confusing, sometimes even misleading, results. Things like your Kewtech obvioulsy can't do dead tests (like IR tests) at all.

Kind Regards, John.

 

[gbasl0]

Hi John,
I'm guessing you are probably a qualified electrician, I didn't mean to offend you I'm sure there are grea ones out there like you. Unfortuantely there are also a lot of not so good ones - and I've met a few.
One was all down for chasing holes in a wall to rewire the upsatirs circuit beauase he could not locate an earth fault - I found the socket with missing earth and wired it up, problem solved - with no need for chasing new wires into walls !
I may also sound daft initially saying this was MCB trip when it was RCD trip, but I'm not completely naive - I have rewired the whole of my previous house.
In the end it is not rocket science a cable comes from the fuse box goes to a socket, on to another socket etc then goes back to the fuse box in a ring.
What I'm planning on doing is taking all the cables out of the scockets and wiring into connector blocks. Find the live wire form the fuse box then slowly reconnect one by one a) to map out the current wiring b) I can eliminate sockets to see where the fault lies. The wiring is quite old, I suspect initially there was one socket then at various times the other two have been added and they tried to put them on a loop but expect it was wired wrong somewhere. Anyway I'll find out one way or another!
I have spare cable so I can put temporary cable from the socket back to fuse board o complete the loop when I connect the first socket, then second etc so should then be able to identify where the problem lies.
I think detecting the problem is the easy (although time consuming) bit, fixing it may be harder if it requires any rewiring under floors etc.
According to the test I have 2 issues 1) earth issue on wires to one socket, 2) incomplete loop on the other two sockets. I think I can find these - but you never know I could prove to be wrong !

 

[JohnW2]

Hi John, I'm guessing you are probably a qualified electrician, I didn't mean to offend you ....

Nope - I am not, never have been and never will be an electrician - and I certainly wasn't offended, nor was I intending to be critical. I was merely seeking clarification. Martin suggested that you you did a systematic series of 'dead' IR tests and you responded...

Thanks Martin - that is exactly what I plan to do.

Knowing that, until recently, you didn't even have a plug-in tester, I was wondering how you planned to do the IR tests. In honesty, I suppose that it was a sort-of rhetorical question, in the sense that I knew you didn't have the means to do such tests, but I assumed that your response would indicate what sort of systematic tests you were going to do.

What I'm planning on doing is taking all the cables out of the scockets and wiring into connector blocks. Find the live wire form the fuse box then slowly reconnect one by one a) to map out the current wiring b) I can eliminate sockets to see where the fault lies.

That brings me back to my question. With the equipment you have, how are you hoping to 'see where the fault lies'. You presumably cannot undertake any 'dead' tests, such as Martin suggested, so I presume that you will be relying on 'live' tests with your plug in tester. As has been pointed out, they can give some very confusing, sometimes misleading, results. However, you could be lucky - so good luck!

According to the test I have 2 issues 1) earth issue on wires to one socket, 2) incomplete loop on the other two sockets. I think I can find these - but you never know I could prove to be wrong !

Without having seen this device, I suspect that the 'red light on the loop test' refers to the Earth Loop Fault Impedance being too high, not to an 'incomplete loop' in the sense that I think (maybe incorrectly!) you are assuming (i.e. a 'broken ring circuit').

As you imply, if the circuit is a ring circuit which has been 'messed with' over the years, it may not still be a simple ring - in which case even tracing the 'arrangement' of the ring, let alone isolating the fault(s) might prove rather (or very) difficult.

Anyway, as I said, good luck - and we'll be interested to hear what you find. Although I'm not an electrician, I certainly would investigate such a fault in my home myself - but at least I do have the equipment to do it.

Kind Regards, John.