A testing week of multiple fault finding

[sparkytim]

Hi Guys

Had an interesting week of fault finding thought might be of interest to some,

1 Farm house Lighting circuit 20 year payback.

Called out by customer to this Farmhouse, MCB on lighting circuit tripping out intermittantly.

Fault History;

About a week earlier owner realised Lights not working in some parts of the house, found 6A MCB tripped (non RCD protected)

Reset looked around for lamps gone, all working OK.

Next day same thing, this time on resetting MCB it tripped out 10 Mins later, reset this time its ok for a day or two then same again.

Investigation;

Take cover off C Unit (Split load to 16th Edition), see two conductors from the MCB concerned, remove both and associated Nuetrals and Test first continuity, L-N, L-E, N-E. One circuit all OK as normal (Low reading L-N, L-E, N-E , High (+99.9 ohms)

Other circuit N-E and L-E 50 ohm fault

Diagnosis N-E + L-E FAULT ?.

Insulation test on same indicates also Low insulation L-E + N-E ( 0 M ohm) as it would.

Locating fault;

Reconnected GOOD circuit and switch back on MCB, go around house and turn on all lights, this identified which areas could be ignored and which were potential fault location, found that faulty circuit affected ALL downstairs and Landing light.

Leaving all lights ON, have a cup of Coffee.

As I was drinking it and chatting with customer, "CLICK" MCB goes out, "Errr". First doubting myself, think Idiot will have to start again.

But just to make sure have a look around and notice in the bathroom one of the 50 Watt GU 10s that had been left on is out, check with customer "It was all ok earlier", so how about that Mr coincidence strikes again!. Could have easily thought that was the original fault and been totally thrown.

So gets back to the hunt, find junction box in loft where circuit splits in to 4 and split off, retest at CU Fault gone, Test at JB leave faulty spur dis and reconnect others connect up at CU and turn on, left with Landing and Hallway lights NOT working so now have target area.

Now this is where things get interesting, still getting 50 Ohm fault, by this time I had recruited customer to Meter watch and shout when anything changed,

Remove landing light lamp and hey presto 50 ohm fault disappears, just to be sure switch Meter to Insulation test and 50 K Ohm fault L-E but N-E fault Gone.

Hummmm 50 ohm was the lamp, but why to earth? Landing light common set up ? BORROWED NUETRAL. trace it out and yes N comes from another JB on the other circuit, so the 50 ohms had been thru the lamp and back to E via the other circuit N. Swopped it over to the correct JB.

Now heres a lesson, faults are not always just a single problem and one fault can hide or affect another.

So what now, well retesting the hall and landing cable showed a L-E fault on ONE LEG of the two way strapper from the downstairs switch to the upstairs, floor board up on the landing, find cable cut it, test down to switch all ok, test UP to landing switch, L-E low insulation on one leg.

Cable under capping up the wall, try and pull it up, no good, so open up hole in wall just above skirting, hook cable and yank up from below floor and up it comes complete with capping NAIL right thru it.

Its a great feeling to actually SEE the fault right there before your eyes, and yes we worked out it had been there 20+ YEARS!, (Before my time on this property) Fault had gradually broken down enough to trip MCB after all that time, but ONLY when two way switch downstairs was in ONE of the two possible positions, hence its intermittant fault history.

Rewired damaged cable, re connected and re tested circuit, had a cup of tea and headed for home.

Have another couple to share a bit later.

 

[roys]

Good bit of fault finding there.

 

[m4tty]

Yeah nice one mate thanks for sharing

 

[Guy]

thanks for putting in the time to share that

 

[SLIPSHOD & SLAPDASH]

Another well done from me.

I dropped a clanger yesterday whilst testing a new job. The job has been running nearly two years now, huge house with 3 phase supply and 2, 24 way boards Cables were meggered and i did R2 wander lead testing ages ago but now most circuits were on i thought i would go round with the young lad and do a complete set of tests. I linked L to E at a board I was getting 201 ohm R1+R2 ( did more tests and found same results on quite a few circuits). I spent ages looking for a bad Cpc, thought about feed through neutral and general head scratching for over an hour and a half. Then it hit me, 3 phase board and i had only linked one phase to earth :Blushing :Blushing:Blushing

 

[sparkytim]

Thanks all. If interested then here goes on the next episode.

2 Dr DIYer and the TT turned to TNCS.

Whilst at the home of my former GP,an avid DIYer ( Have you noticed a lot of "proffessionals", Drs, Dentists and even Vets, fancy themselves as Electricians?, sorry Patch none intended)

wiring out his massive new conservatory, (well on 100 grand a year they must have to spend some of it), I just did a quick Zs on an existing socket and got 1.2 ohms. Thats good I thought especially as this is a TT installation and I new last time I tested the Ra it was 169 ohms!. As a matter of interest I also did an RCD test and NO tripp @ 30 mA none @ 5x and none even on a full 25 Amp Loop test.

So what have we got here? A TT install looking more like a TNCS and No RCD protection.

Check RCD test button and Click Off it goes.

Now having been around the block a few times I recall something like this happening in the past, and remember N-E faults can disable RCD s on a TT.

So remove cover off CU (Double decker Duel RCD job) test Other Rcd and all tests ok.

Stick Meter across between N and E on continuity and see 1 ohm, remove Nuetrals one at a time and discover fault on downstairs lighting circuit.

Leave disconnected and now do a Zdb test, get 64.1 ohms, thats more like TT and even better Test the RCD again and yup all OK. (26.7mS @1x and 16.5mS @5x)

So just to analise things this N-E fault had disabled the RCD and turned the install into a TNCS, only trouble being instead of a nice fat 16mm Earth lead, any fault current would be taking a scenic route around the house on a 1mm (i.e. a L-E fault on the cooker for instance would have travelled back from the cooker on its cpc to the earth bar in the CU, down the faulty lighting circuit 1mm cpc to the N-E fault and back up the 1mm N to the C Unit and off in search of home via the N supply conductor to centre point on the supply transformer)

A previous example of just this scenario that I have seen had resulted in a Burnt out 1mm Twin and earth from Cu right thru the house!

Well the Dr was in the house and very interested in all this, passing by now and again with nail gun in hand, (Dont ask, but think he had a floor panel to fix down in the loft)

So as he passed by on route to rig me a scaffol platform to refit the Landing light fitting "While your here", (4 bits of 3x2 and a 6"strip of chipboard) I ask "has he fitted any new lights downstairs lately? " not recently, was the reply, no clues there then, so set about seaching for the fault.

Split the lighting circuit at a convenient point in the middle and fault disappears, good its further on then, all wall lights from here wired in singles, N looped in and out of all fittings, L looped in and out of all switches with switch wires to fittings.

Split N at wall light in hall, fault further on, into lounge ( 3 wall lights, split at one, fault further on, go to next one in room, fault back between the two. Now what could be between the two wall lights? search high and low, nothing in the room, getting late in the day now, so leave 2 walllights dis and prepare Dr for return visit and possible floors up above, NOPE laminated (dont you just love the stuff), well holes in ceiling then!

In between all this I dice with death on the landing scaffolding and re fit the landing light,(Dr had put his foot thru the ceiling previously and builders had been summoned by the wife to repair the damage which ment them taking the light down)

So back a few days later to finish the job.

Dust sheets at the ready Mrs Dr is all prepared, but having slept on it, I wonder what route the N took between the 2 wall lights, and take a look at a wall light in the Dining room which may have been on route for convenience, and yup there it is N short to metal back plate. Great Mrs Dr is very pleased, we celebrate with a coffee.

And yes Hubby had fitted same Wall light a few years ago. They had been very fortunate not to had any serious faults to earth in the meantime.

All in a days work, role on legislation to prevent such like events in the future, oh forgot we have it already Part something or other......

PS

For all you budding sparky's out there (NO LLs PLEASE), would you like to have ago at explaining what would be the normal result of N-CPC short on a TN install with an RCD and why the RCD was disabled with it on this TT Installation.

 

[sparkytim]

Have a couple more (what a week), Mopping up after the ELECSA man and saving a customer 5 grand, be back later.

 

[a1]

2 Scoobs issued, mate.

 

[sparkytim]

[]Thank you very much.

And theres more;

3. Mopping up after the ELECSA man.

Now just to make it clear this is not a pop at ELECSA, this guy could well be a DI registered with any one of the scams, but just goes to back up what many of us on here have come to realise as to the devaluation of trade body membership in recent times.

Guy phones me " are you a proper lectrician?",

"Well I like to think so, how can I help ?"

"Just had a socket fall off, can you fix it and quote us for some more work?"

"Certainly can, will call in later this afternoon"

So duly calls round on my way home to take a, look, expecting to find a surface socket hanging of the wall perhaps.

Met by the prospective client opening the door just cleaning himself up from decorating, and he duly leads me into his sons bedroom, all nicely painted out and shows me a double socket hanging of the wall, it had "Fallen" off its live conductors just hanging on CPCs! . He had loosened it off its FLUSH back box to decorate and been flabagasted to see it drop off all 6 live wires, (3 L + 3 N, being a point on the ring with a spur off it to an external socket)

Now Mr decorator was not amused, as he had paid VERY good money to this Guy from ELECSA to wire this point and others, along with a new Consumer Unit, Garage supply and bathroom lights.

Well recoiling from the shock and trying not to over dramatise things a politely ask where the Consumer Unit is and am ushered back to the entrance hall to be further surprised to see a shiny new Consumer Unit with 30 m A RCD incomer (Main Switch). "Ummm, thats not what we normally fit now adays", I isolate and make safe the socket before looking at the additional work required.

As we do a tour and I jot down his requirements, I am given further tails of woo about the ELECSA man, and realise here is another example of what is giving us a bad name.

It turns out he came in with the bathroom fitters and was asked to do additional work, but they came to see it had not been such a good idea, they had called him back 3 times and Granny was getting fed up. She lives over the road and acts as key keeper as both Mr and Mrs work full time.

Well I email my estimate and get a ring to say go ahead, on the agreed day me and mate turn up and, granny lets us in, "I'll be back to make you a drink- do you boys stop for one? that other p........r never had the time, I warned them he was rubbish after his first day, should have seen the carnage, couldn't even get them sockets straight".

Now I have the greatest respect for Granny's, they have been around along while and have a good sense of whats ok and whats rubbish, pity they didn't listen to her at the start.

We crack on and just on schedule Granny comes back and makes us coffee, we get the full story of the nightmare so far and wonder what else we will find.

All goes well and looking like an early finish, just the testing to do. Should have known better, as I take the cover off the C Unit (Isolating first of course), I brush a 6mm with the cover and out it pops from the MCB! Have a look and the screw is done up tight but the conductor had never been in the tunnel, just tucked down the back of it.

Lesson here ALWAYS give um a tug after you tighten up a terminal, anyone can miss the tunnel, but no excuse not to check its home and dry. Seen to many burn outs from loose connections over the years, good job this was just the new Garage feed with no great load involved, if had been a cooker or shower 6mm that could have been a different story.

Looking at this install in a bit more detail also notice an unothodox main earthing conductor arrangement, nice new bit of 16mm 6491x leaving the earh bar but then going into a single pole henley block next to the CU with two 6mms coming out, check in external Meter box and find the other ends going into the series 7 cutout PME earthing terminal. So probably this 12mm main earth would meet an adiabatic equation calc. but think it highly un-likely our friend did the maths to prove it.

So we have a non compliant Install on several fronts ( Reg 314 (i)

for instance?), some sloppy workmanship, what else is lurking? Its not long before we find out, on checking the one and only Ring circuit for continuity, L-L good , N-N ok, same reading, CPC-CPC >99.9 ohms. Just check incase its not the right pair, been caught with that before, but no continuity with any other cpc on either legs. Great - dis on ring cpc somewhere. Now I don't know about you but when replacing a Consumer Unit a very basic test would be to prove an existing ring is a ring.

Get seaching, mate watching meter as I nip round all the sockets with a L-E shorted break out plug and prove all ok around the ring untill the last but one socket before the return to the CU, swop meter over to other leg at CU and prove ok at first socket but not at 2nd, so break between 1st and 2nd socket, drop of both hoping to find cpc popped out or broken but all looks good, pop up into loft to check if JB between the two, and yes there is but checking it out no joy. Put a L- CPC short on at this JB and prove fault is down from it to a single socket in kitchen below.

Now Kiitchen fitters are great with worktops and tiles but a nightmare with wires, I know the plan shows were wall cupboards must go, but a 6mm drill bit has no respect for pvc oval and twin and earth in side it. So not wanting to desimate the kitchen we decide to turn this single socket into a spur utilsing the remaining good cable and abandon the faulty section, quick visit up into the loft manage to cut in another 30 amp JB and isolate the kitchen fitters colateral damage. Re check continuity - all now ok, Cross over and get R1+R2, at CU and check at all sockets, identify several spurs but no more then the number of points on the ring so all ok. Hold our breath as we do the insulation test but feww all >299 M so thats good then. Rcd tests all ok as well.

Now you would think that was enough ammunition for a public execution, but no, our sojourn in the loft had thrown up a further dabarcle, see pictures attached, no comments needed.

ATTACH=CONFIG]3513[/ATTACH]View attachment 3511

 

[professional]

Another well done from me.I dropped a clanger yesterday whilst testing a new job. The job has been running nearly two years now, huge house with 3 phase supply and 2, 24 way boards Cables were meggered and i did R2 wander lead testing ages ago but now most circuits were on i thought i would go round with the young lad and do a complete set of tests. I linked L to E at a board I was getting 201 ohm R1+R2 ( did more tests and found same results on quite a few circuits). I spent ages looking for a bad Cpc, thought about feed through neutral and general head scratching for over an hour and a half. Then it hit me, 3 phase board and i had only linked one phase to earth :Blushing :Blushing:Blushing

Now how many times have I installed a dual rcd "high integrity" board, switched on and everything is as dead as a dodo - then realised I`ve not put the ******* busbars in? ..... :coat

 

[Sidewinder]

Fitted a triple split one last week, main switch 2xrcbo, 2xrcd with the rest of the circuits.

All working bar the RCBO fed circuits.

Looked, all seemed OK.

Pressed the test buttons on the rcbo's nothing!

Oops, no bar!

Doh!!!

 

[ProDave]

Well I can beat that.

CU swap a couple of weeks ago.

As soon as the new CU was in place and tails were connected, I thought I would re energise and measure Ze.

What, no power to CU? WTF is going on?

Then neighbour comes round "is your electricity off as well?"

Power cut in the whole street. No I didn't blow anything up.

 

[NozSpark]

LOL

I hate it when that happens

 

[peterkenney]

sorry om very new wots a zbd test please

 

[Zeespark]

An EFLI test at a sub main.

AndyGuinness

 

[sparkytim]

It never ceases to amaze how often those sorts of things happen.

Well here goes Episode 4

SAVING A CLIENT A FEW GRAND.

Now I am not the cheapest sparky in town, as often I realise on failing to get the job, but this next example takes the biscuit in "up selling" as i believe they call it. ( Testing is a major issue in the story so bare with me if you please)

Called up by the charming Jane, local Manager for a Housing rental company with several elderly persons Housing complexes in Town.

"We are having some bother with our sewerage" she says, "can you come and have look?"

Not being overly keen, but wishing to please I call by. This complex is a converted Maltings building on the edge of the southern most Norfolk Broad (which actually happens to be in Suffolk just to confuse things) 60 apartments 45 for the elderly and 15 posh ones for the better off.

Thing is its at a low level on the waters edge with the main foul water system at a higher level. Phisics dictates that gravity needs some assistence to achieve this, hence there is a chamber and pumping system to push the stuff up hill.

I am a great believer in all to their own and this is not my chosen field of expertise, but the local specialist company having been called in to rectify some problems had duly condemend the installation cabeling and quoted several thousand pounds to "rewire" it.

Being very on the ball Jane and her boss thought it may be prudent to obtain a secound opinion, hence my summons to site.

The caretaker met me and explaned the issue, having delt with a pump blockage problem the firm had been called back to to a permanent High Level Alarm from the control panel for the system and come up with their diagnoses. Having had the unpleasent experience of a real high level within the chamber and its back up, the ground floor occupants of the posh part were in a state of nervous exhaustion awaiting imminent arrival of unpleasent things forwarned of by this alarm so urgent action was needed.

Lifting the chamber manhole cover we were met by a charming site, in the depths a steamy sea of you now what and at the top of the chamber everything a wash with the resultant condensation. Amidst the abundant moisture were 4 SWA cables terminated into an IP66 adaptable box from which 5 flexable cables fed two 3 phase pumps and 3 float switches, connected via IP68 connectors, all drippng wet.

Now my powers of observation being acutly honed picked up on a faint possibility that water ingress may be an issue here.

Added to that the fact that ONE of the IP68 connectors was wrapped in DENZO tape aroused my suspicians.

Checking thru the steam we confirmed that indeed the said connector was for the HIGH LEVEL ALARM.

Replacing the cover and taking a welcome breath of bracing fresh air, we made haste to report our findings to Jane.

My guess was that this connector was letting in water and causing a false alarm, mosy likely the 25 year old undisturbed SWA cables were still fit for purpose.

"So how can we prove that" comes Janes enquiry. TESTING is the only way was my reply.

Can you do that for us then and submit a report.

Having been put off by bad weather a couple of times a fine Monday morning found us back on scene.

JC, my loyal mate, was duly reminded of risks involved messing around with this 3 phase stuff and set up at the panel end, having achieved a safe isolation of the system, key to switch room in my pocket, I perch over the abyss and attempt to remove the IP66 junction box lid, 2 screws co-operate but the 2 the other side refuse to budge, I have to lever open the cover to gain access, surprisingly only a small amount of condensation is observed inside.

With walky talkys crackling we DISCONNECT and test each SWA in turn, continuity using the armour as a return all conductors prove good low resistence, then on to Insulation testing, 3 Phases to earth, then between each phase conductor and each other, all >299 M ohm. Next the control float switch circuits, good low continuity and high insulation readings. Part way thru one of the Radios packs up, I do my Basil Fawlty impression, you use them once in a blue moon and when you really need them, they pack up on you, typical, typical.

Noting the sudden loss of comunication JC comes wandering round to check if I have disappeared into the mire, not sure what his plan of action was but he seemed pleased to see me still around. We decide to use our mobiles to complete the task, only trouble comes when I knock it over the edge and plop its gone forever, JC did not seem to keen to recover it so later in the day I have to buy a new one.

Fortunately we had completed the part of the task requiring remote communication, but JC notes the level in the chamber is getting a bit high. With images of screaming Tenants fleeing the building we hurredly put things back together and re start the pumps, just in time the level once more drops to safety.

We break for coffee and fresh air. On return we isolate once more and quickly test insulaton resistence to earth of the Pumps and float switches and guess what, Pumps and 2 float switches OK but the High Level alarm float switch thru the denzo'd connector is LOW insulation, surprise, surprise.

We remove the Connector from circuit and check the float switch for continuity, pulling it up to surface, we check its operation by tipping it from vertical to horizontal and find it does not switch, so here was the real fault a permanent made contact that would expalin the permanent High Level Alarm at the panel.

A report is compiled confirming that the SWA cables are in GOOD condition and DO NOT need rewiring, a new float switch and connector will solve the problem, net result several Thousand pound SAVED. We return to replace the offending items and all is back to normal.

Jane is well pleased and has great delight in emailing the Pump specialists with our findings. However the boss of same digs his heels in and insists his Engineer is well qualified and trusts his findings. A duel is suggested, Meggers at dawn, two appointments are made and broken by Pump boys, but at third attempt they turn up.

Trying to be as polite as possible I make comment on this being the wettest drought ever, no response, the lid is lifted and 3 phase connectors un plugged, NO SAFE ISOLATION, I keep quite, I have to keep telling my self I am only here as an observer, THEY are here to prove THEIR assertions.

We wander around to the Plant room in silence and our friend switches OFF the supply, well better late then never, gains access into the panel and disconnects the Pump circuits INCLUDING THE CPC tail. I make no comment but await a result," all good there "is the finding. I agree, how about the 24 volt control float switch circuits?

Now my suspicians are confirmed, he Disipates 500 Volts from his shiney new Megger 1752 between the earth terminal and conductors with them still connected! "Oh there well low" he says. Now here I just can not help my self and suggest it may be better to DISCONNECT them. He reluctantly goes back outside and disconnects the far ends, comes back and tests AGAIN with panel ends still in. I now point out that he has just meggered INTO the equipment. He mutters something under his breath, disconnects and trys again. ALL GOOD, we agree the SWA are in tip top condition.

Having acheived a result I now let on what we had found and replaced, he returns to base with the old float switch and a copy of my report for his boss.

30 Mins later Jane receives an email of apology, with an interesting explanation for the error on their part.

Another Pump company is now tendering for the contract.

I wonder how many others are out there with nice shiney Installation testers giving false information.

As I was taught in assessor training, no one is useless, we just identify Training needs.