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PEG

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It would be nice to get to the bottom of this fault,but,i would like to tip my hat,to the OP,for a refreshingly open and candid post.
The man that never made a mistake,never made anything,and it is job stories,such as this,which can keep even experienced hands,from forgetting the hazards which abound.

Marconis drawing,reminded of a large council workshop,where the spark had shut-down the power,and removed the main DB.....before discharging what may have been,an entire floor of broken florries,via his left thumb...

There was no site power,apart from a couple of small generators,and he was on for blaming the contractors for back-feeding,before it dawned on him...Believe nothing you hear...and only half of what you see ;)
 

marconi

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PEG's #36 and ROHT's anecdotes are great ways to warn and train people. When I was brought in to sort out the mess after a contractor was electrocuted by 11kV I introduced these 'tool box' talks for my technicians. I was always on the lookout for folk with a tale to tell which rammed home the point of 'no short cuts to safety'. Much, much better than a dry lecture on the subject. It's the setting and context which provides the engagement and learning. As humans we remember stories which is indeed how folk passed on information and learning in those days when they could not read or write or there was no paper or books.

One of my 'favourites' is the computer technician who shorted out the live 5Volt busbars of a Ferranti FM1600B computer with his gold wedding ring - yes he had done the training, there were warning signs for very high current and to remove hand and arm metal jewellery, he had checked busbar connections hundreds of times before but on this occasion he lost a finger, because ......
 

Wilko

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Hi All, late to the party I know, but here’s 20p from me :) .

Recently, I investigated an EICR C2 fault for high leakage. I did find the fault wiring with the usual application of time and patience to work through a couple of false starts (well no one’s perfect, not me anyway). I ended up with house global IR of about 90 meg Ohm and a leakage of about 6mA. Which made me think - why is it so?

Of course it’s the capacitance to earth of the L conductor and a direct consequence of running the CPC together with the Lives. But how much leakage is reasonable? I got a new 100m roll of 2.5/1.5 and just connected it up - 1mA earth leakage. Add up 10 circuits and even with no loads we see another reason why we don’t remove the Earth on a live installation...

I’ve added the hurt graph to illustrate - blue is ok, green is not good, yellow makes me bellow and red I may not be posting again.

C9AEB4B3-6CD5-46FD-8896-7D143374C0CB.jpeg

2944F81E-BCD0-4E67-A3AF-0739ACF87D8A.jpeg
 
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TheReturnOfHightower

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Right then chaps, sorry I didn't post yesterday but council sparks came out Monday and got to the bottom of it. Bottom line is, it was a loose neutral causing the fault in 3 lights.

So, to talk through the actually wiring of it, all lights on the bank are fed from a single switched line, with the exception of 2 & 5 that have an additional perm line for emergency. Lights 1-3 are fed by 1 neutral, lights 4-6 are fed by another totally separate neutral (independent all the way back to the board). Other banks are seemingly wired the exact same, 1 line 2 neutrals, so this looks original wiring instead of bodged repair. The loose neutral was at a junction box upstream from lights 4-6, hence why only these 3 lights were faulty.

So, I got a belt, and I think the reason is, I separated the neutral after light 3, what I thought was the link from 3 to 4. Because I'd left the emergency connected and had only isolated at the switched line (wrongly thinking light 2 was upstream and therefore wouldn't be affected by me breaking the neutrals). Instead of breaking 3-4 neutral link, I broke 3's neutral back to the DB and hence the belt. Yep, it's my own fault - safe isolation would have prevented it, and I've learned a massive lesson.

However, anyone know why it may be wired in such a way?
 

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James the Spark1976

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Don’t know the layout,
Could be it was designed so it could be split into 2 separate zones with a partition?
 
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TheReturnOfHightower

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Don’t know the layout,
Could be it was designed so it could be split into 2 separate zones with a partition?
Nah, big assembly hall, always been like that since day dot. I'd surely expect to see spare line conductors in the trunking though if they'd altered the circuit over the years. I'm not writing you off by the way, I'd love someone to tell me the answer but me and 4 council sparks couldn't come up with it.
 
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Lucien Nunes

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Maybe they were just too tight on voltage drop, decided to spread the load between two cables but only bothered on the long straight run of neutral rather than doing the same with the switched line?
 
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TheReturnOfHightower

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Maybe they were just too tight on voltage drop, decided to spread the load between two cables but only bothered on the long straight run of neutral rather than doing the same with the switched line?
I like your thinking - it's got to be something like this surely, but the circuit is run in 2.5mm which for a lighting circuit that has a furthest point about 30 metres from the DB, doesn't sound like it would struggle.
 

davesparks

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I've wired circuits in a similar fashion once or twice with duplicated cables for no apparent reason.
What actually happened is that with two of us working on the job we both thought the other was pulling a different circuit/cable but actually we were doing the same as each other. Usually when we're working long into the night to get a job back on schedule.
 
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TheReturnOfHightower

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I've wired circuits in a similar fashion once or twice with duplicated cables for no apparent reason.
What actually happened is that with two of us working on the job we both thought the other was pulling a different circuit/cable but actually we were doing the same as each other. Usually when we're working long into the night to get a job back on schedule.
Have you ever done it with 5 circuits, in mirror of each other, by total accident? :D
 

marconi

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I think it is an attempt at what Lucien Nunes described at his #17 to obtain more even brightness from all the fittings in this large assembly hall - but the electrician only wired it 1/3 correctly - for fittings 1-3. He should have taken the second N to fitting 6 and 4-6 should take their line by a connection from fitting 1 to fitting 4 (or other permutations which arrive at a similar effect).
 

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