Consumer unit change nightmare and some questions

[sambotc]

Carried out a consumer unit change yesterday, haven't done much of this before, mainly testing new circuits i've installed.

So the actual consumer unit change went ok, i'm going to show this job to my assessor for CPS so wanted to make sure everything was tip top. I upgraded the meter tails to 25mm, main earth to 16mm, main bonding to 10mm etc.

First mistake I made was to do the testing after installing the board!

How do most people carry out continuity testing on lighting circuits? Most of the light fitting weren't pendants so I seemed to take ages messing about with different light fittings taking them apart etc to get to the terminals, really frustrating when the wiring was shoddy, cables coming out of connector blocks etc the loop terminal was often stuffed into the ceiling void etc

Is it acceptable to test continuity R1 & R2 etc from the switch itself or will the reading of the switch wires cause inaccurate readings?

On to the ring final, which is 1 circuit for the whole house and no R1 or Rn continuity :thumbs_down: started to split the ring and found that the wiring in the kitchen had been bodged, ring had been extended connector blocks everywhere, knew it was going to be problems. Figured out what was the original wiring and reconnected in the same configuration and all was good. Thought i'd run all the tests as is so left the 3 new sockets disconnected.

Went on to IR L-N , fail. Split the ring in the same place as I had just reconfigured and tracked it down to one side of the kitchen. Took me ages to find the culprit which was a hidden socket under the kitchen sink which had burnt out. New socket front ideal.

So went back to look at the wiring I had disconnected, after some tests I found out the numpty who wired the kitchen up had got his wires crossed (literally) and a switched fused spur that was supposed to switch a built in freezer (that I had turned off to carry out testing) was switching the ring main in half!

So, rewired the offending sockets/switched fused spur and retested continuity, all was good. Re-test IR, L-E fail ..... FFS!

Cutting a very long story short, dismantled kitchen and built in freezer and fridge, to find that the freezer had been hard wired into fused spur with no means of isolation. Disconnected freezer and all was good. Re wired freezer into fridge fused spur so that both can be isolated fron the same switched fused spur above worktop level. Is this acceptable?

Retested IR L-E only to find the fault had disappeared even though there was no obvious reason for it to fail other than an internal fault?

Any ideas?

IR was coming back a 0.09M ohms, and I was surprised the RCD didn't trip on the new board????

By this time the customer was obviously well cheesed at the previous electrician, I had started yesterday morning and by the time I had figured out what was going on each time etc (bearing in mind I am still sort of fumbling my way through these tests a bit, trying to guess where the wiring goes some sockets with 4 cables in the back which disappear behind tiles)

Anyway it all finally tested good, one thing I noticed was how much the IR test changes when fixing the socket fronts back, approx 5-10M ohms less every time, is this normal I just put it down to the cables all being jammed together? Started around 300M ohms and I tested after screwing back each fascia and noticed this approx drop each time.

So, as you can tell, my first EICR really put the mind to test, but kind of glad it happened in someone's house I knew and also so close to home! Good experience, but are they often like this or was I just unlucky? I know I probably spent a lot more time on identifying the faults compared to someone with more experience in this kind of thing.

How often do you come across things like this and how would you handle the situation, would you just record it on the certificate or are you obliged to find a fault when IR is that low?? Not that I would want to walk away, but in another instance the customer may not want their kitchen dismantled or pay the extra time to find the fault?


Thanks in advance, sorry for the long post, been a long job!

 

[ezzzekiel]

If as in the beginning of the thread you say you mainly do testing then why the long thread about the testing side? Bit puzzled

Could you bullit point the main areas of your post for discussion thread was a bit long for my little brain

 

[telectrix]

shows the importance of doing a few tests before the CU change, but well done for your perseverance in tracing and rectifying the faults.

 

[telectrix]

If as in the beginning of the thread you say you mainly do testing then why the long thread about the testing side? Bit puzzled

quite a bit of difference between testing work you have just installed and an old installation that may have several faults, mostly man made, or should i say muppet made.

 

[sambotc]

I only really have testing experience on radial circuits (solar) and sub boards that I have installed myself. I'm starting to get some electrical work enquires for this kind of thing now though, and also my level 3 inspection and testing course starts on the 9th July which I am hoping will answer some questions.

 

[ezzzekiel]

Yeah but he knows how to test and obviously knows how to find and correct any problems so I'm missing the thread relevance

 

[ezzzekiel]

Ah now I get it, vast majority of properties will have anywhere between one and a dozen faults to find after years of bad electricians DIY works etc

You appear to be doing the right thing just got to get used to it I'm afraid

 

[sambotc]

I asked the questions because I like to do things right and by the book (well, except when it comes to the main fuse) and also I am coming across things that i've not experienced before, so although to the book these things are correct,its encouraging to here what other, more experienced members think of the results I have found.

I'm the first one to admit that I don't have much experience in these situations, and unfortunately I'm not in a position to work for free to gain experience off the back of another spark. I'm self employed and as we all know work is thin on the ground at the moment for a lot of people. that said I am not going to take on work that I am not comfortable with, hence asking the questions and hoping that someone can verify my findings and how i dealt with them (rightly or wrongly, happy to receive constructive criticism)

Is suppose the alternative could be just to presume what i'm doing is right and potentially leave a trail of errors for someone else to come and tidy up after me?

 

[telectrix]

yep. last week i was on a fault, low IR on lighting. the actual problem was a burnt FCU tracking L-E, but in tracing through 9 lights, i had to redo about 5 bodged connections in fittings. after doing each one, found the fault still there on the outgoing cable. as you might guess, the FCU was on the last light in the circuit, feeding a fan.

 

[sambotc]

Thanks ezzzekiel and i hope the above post didn't come across as funny which reading it back, it may have (un intentionally)

 

[sambotc]

Thanks Tele, where's the thanks button gone by the way?

So, do you charge a set price for a CU change, and allow a reasonable amount of time for rectifying faults, any thing above and beyond you charge at an hourly rate for example?

Also, what would a low IR reading code as, and also, would have expected the RCD to trip with such a low L-E IR reading 0.09Mohms?

 

[telectrix]

I asked the questions because I like to do things right and by the book (well, except when it comes to the main fuse) and also I am coming across things that i've not experienced before, so although to the book these things are correct,its encouraging to here what other, more experienced members think of the results I have found.

I'm the first one to admit that I don't have much experience in these situations, and unfortunately I'm not in a position to work for free to gain experience off the back of another spark. I'm self employed and as we all know work is thin on the ground at the moment for a lot of people. that said I am not going to take on work that I am not comfortable with, hence asking the questions and hoping that someone can verify my findings and how i dealt with them (rightly or wrongly, happy to receive constructive criticism)

Is suppose the alternative could be just to presume what i'm doing is right and potentially leave a trail of errors for someone else to come and tidy up after me?

no, i think you have approached the problem correctly. even the most experienced sparks can get bogged down sometimes. IMO experience may make you faster, but not necessarily better.

 

[sambotc]

Thanks again, encouraging to know

So just to recap on a question if you don't mind replying:

How do most people carry out continuity testing on lighting circuits? Most of the light fitting weren't pendants so I seemed to take ages messing about with different light fittings taking them apart etc to get to the terminals, really frustrating when the wiring was shoddy, cables coming out of connector blocks etc the loop terminal was often stuffed into the ceiling void etc Is it acceptable to test continuity R1 & R2 etc from the switch itself or will the reading of the switch wires cause inaccurate readings?

thanks in advance



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[johnboy6083]

ive just finished an EICR on a commercial premises, and i too spent absolutley ages fault finding. Theres no hard and set rule on how long it takes. The experience helps when for example seeing a reading to a round figure on IR, 9 times out of 10, it means a load is still connected, determining the way cables are ran, and identifying switching arrangements ect. You have a feel for what you should be seeing, and know if something still complys with a test result, but doesnt seem right ect.

The one thing i beleive is that the inspection is just as important as the test. Youm may have a good reading on a cable ect, but it may be deteriorating badly, and needs remedial work.

Like this:

 

[telectrix]

try using a wander lead and just measure R2. remember to subtract the lead resistance, or null meter with wander lead in circuit. ideal solution for metallic fittings, no dismantling involved.

 

[telectrix]

sometimes the thanks button and like button dissappear if you post simultaneously with anotehr post. do a page refresh and they come back.

 

[johnboy6083]

IMO, with lighting circuits, the only way to do it properly is to test at each point, unless you can see which one is last in line. Even then i beleive sampling is required to ensure that connnections are good ect. As normal, if its bad, then increase the sampling. aking ages to take them apart is part iof the job, and one that the half day PIR's / EICR's probably dont do.

At the end of the day, if that house burns down, you may well be questioned, and could you live with yourself if you didnt test something, even if it wasnt your fault?

 

[sambotc]

Is it standard procedure to carry out a full inspection as well as testing on a CU change? obviously you can't connect a circuit without testing it prior, but I thought the inspection side of things taking off all the socket faces etc would possibly be above and beyond the requirements for a CU change. not to say that it isn't advisable, i'm just thinking of cost etc

Also, tele, how do you calculate or measure Zs without an R1 reading?

 

[johnboy6083]

try using a wander lead and just measure R2. remember to subtract the lead resistance, or null meter with wander lead in circuit. ideal solution for metallic fittings, no dismantling involved.

You still need to check polarity, and the only safe way is either dismantle and test at terminals or using a plug in kewtech type, in which case normal R1+R2 xcan be measured anyway.

 

[telectrix]

Also, tele, how do you calculate or measure Zs without an R1 reading?
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you can't. lighting can be a nightmare with all the different fittings. you also have to bear in mind that anything you dismantle may then introduce a fault, due to being disturbed. a general approach for CU changes is to either do a full EICR first, or just test for bad IR's, shared neutrals and a quick visual, with a rider on the quote that any other faults coming to light will be charged at hourly rate to trace and rectify. makes our job so difficult when joe public thinks a CU change is £50 for the CU from b&q and an hour's labour to install.

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