Electrical Diagrams

[vaughant]

And the importance of being able to read them.

This is a subject that really concerns me with the apprentices where I work and the management staff.
They appear to put no emphasis on what is IMO a fundamental part of electrical control,they seem to prefer getting these lads to either ask someone what the fault is or try guessing first which to me is ludicrous.
I'm not saying I'm perfect (although I have got nice eyes) but I feel I can approach most breakdown situations and given the correct documentation have a damn good chance of saying it's this or that and not just plucking ideas out of the sky that I so often see folk randomly changing components then still looking baffled when it doesn't work.
Of course it's handy to be more lucky than clever but in the real world(or my world at least) luck is a scarce commodity!!!

So,I'm thinking the great folk on here who deal with such instances everyday could maybe contribute some help on this matter with of course pictures and explanations being preferable.

Hopefully this can become some sort of a reference for our good folk who want to get into this relatively untapped field of electrical expertise,after all there's a lot of people out there fitting lights and sockets and as the competition becomes greater in those fields it's my belief that more than a few will look to diversify into the industrial control game.

In my experience our German brothers and sisters do make a damn good diagram but it does require a bit of brain work to see how it all works,again I could be preaching to the converted but I have been amazed by 2 very experienced lads at works inability to even read a basic control diagram,unable to work out where power comes from,not even 100% aware of n/c and n/o switching symbols,fuses,mcb's and forward reverse contactors.

I'll start with this as a basic example.
We had a fault in the week with this motor and I was asked to let the apprentice (3rd year) to lead the way,couldn't get this contactor to kick in.

Sorry for pic quality.
He stands there with the usual teenage blank expression so I tell him to see what we've got.
He starts rambling and tries a few pointless things like checking nothings tripped etc when I ask him what were looking for.
He has no clue.
We want 78K1 to come in to move the motor towards the wall (shuttle car).
Now,from the diagram under 78K1 is in smaller writing 78.1,apprentice has no idea what this means.
This relates to the page in the diagram where I can find what operates 78K1.
So we go to page 78,section 1,just like a map grid reference .
There we find this.

Jeez I'm sorry for the quality,I'm hoping people with better than an old iPhone camera will chip in!!!
Now,it shows a plc output,an n/c contact from 78K2 before we get to 78K1 A1 then through A2 down to 0v.
People who are familiar with this will know that A1/A2 generally relate to the connections of a contactor coil but those new to this can see it's represented by the symbol of a rectangular box,this often has a diagonal line through it.
In british drawn diagrams it's often shown as a circle but the A1/A2 should give it away.

When control voltage is applied to this coil,it should if working correctly energise and in turn pull the contacts in on the contactor allowing three phase out of the bottom of the contactor and off through various wires to the motor windings.

I then got the apprentice to make the next move.
Again after head scratching it meant me talking him through it.
I got him to check for power at the coil,A1 to 0v rail,nothing showing.
I then got him to check from PLC output A88.0 (A or Q are often used as output symbols, I and E as inputs),we had 24v dc.
The next stage was to check what we had at 78K2 terminals 21/22.
This is where experience comes in,often parts are changed with non original manufacturers ones instead which do not always use the same markings.
This was not the case here but if that occurrs again,the diagram can help as it shows us that were looking for an n/c contact on 78K2.
We tested there and found power to terminal 21,but nothing on terminal 22.
A quick power down and switch to continuity on the meter told us the n/c contact was u/s and therefore needed replacing.
This job came to my attention to look at because the previous shift had:
Changed 78K1 contactor
Attached a laptop to the s7 plc to read it
Belled out the motor and found nothing wrong.

Not a diagram in sight.
1/2hr later the machine is working using only simple test procedures and an electrical diagram.

Please feel free to add,again this will I hope be more of an aid too less experienced folk.

I'll get some plc stuff up to look at too as the principals are the same.

 

[Knobhead]

Nice one vaughant. I’ll be honest I don’t like modern A4 drawings where your jumping from page to page, I’d much rather have a big A0 sheet. But that’s my personal choice. As for teaching apprentices there have been times when I’ve been near to throttling them.
Us oldies can be as bad, (not me) the number of times I’ve had the same situation as you. Well we changed that, but it still didn’t work. “How far have you got through the sequence.” They hadn’t even got the drawings out! Just jumping from one guess to the next.

My idea of a drawing.
View attachment 11236
It’s for an auto close OCB. Bits of it may look a bit weird as there’s a lot of CT’s used which are referenced to earth.

 

[spark 68]

That drawing is fairly clear as to what is what Tony, I have had to build stuff similar to this and Vaughants diagram above, with far more cryptic drawings than either of these.

 

[spark 68]

I agree with both of you though wrt to playing guessing games, the only way educated guessing sometimes works, is if you know by experience a particular component is prone to failure.

When I was shown the ropes, I was taught to stop and think first, about what is not happening, and what is happening, this can rule quite a large section of the circuit out, and give a clue to where the problem is likely to lie, or at which stage.

I was also shown how to hit a stage> miss a stage, and only stepping back one step when something is abnormal/un-expected. This can cut the amount of testing by half, but this can sometimes be difficult when you have multiple feedback paths or outputs of one section affecting inputs of another giving misleading results, or if there are multiple faults.

One thing is guaranteed, which ever end of the Fault chain you start at, the fault will lie at the other end!

 

[sjj84]

The problem comes when you go looking for drawings and they're missing! Or as we usually find, the drawings are so old they're no longer relevant!

 

[Bobster]

A big problem on my site is people not updating or archiving drawings properly.

 

[silva.foxx]

@vaughant; this is something I will be covering with our apprentice and you have explained it well.

@sjj84 and RoB2; missing, incomplete, poor drawings is my pet hate. When I do a project I like to trace out what we have, cross-reference with the schematics if we have them then modify to complete. I then like to upgrade the schematics in... wait for it... MSWord... or AutoCAD if I can be bothered! I know for a fact that recent in-house projects in work have been done without the provision of schematics. How can you create a control system with no schematics?

About 9 years ago, because I'd done a course in CAD I was asked to upgrade some schematcs that were over twenty years old with pencilled-in changes/upgrades with supplementary smoke-packet sketches. These are a sample I provided (kept in the original format)...
View attachment SVK10.pdfView attachment SVK05.pdfView attachment SVK09.pdf

Must agree that the German stuff is very organised and keeps you on your toes!

To be good at schemtic reading you do have to put some effort in and practice on different formats.

 

[plugsandsparks]

I think you are touching on the fundamental problem in our industry. Its not the apprentices fault per-se, but what training have they actually had and are we attracting the cream of our profession.
I don't know what the answer is and i can understand " management" using a "have a go" approach, what choice do they have? The skills are not there.
Persoanlly i don't like going anywhere near control without a drawing at least to work with, not overly stressed if its not perfect but at least it enables me to find my way around.
Good news is, decent control sparks will always be in demand

 

[Knobhead]

Having done some major alterations to a control system I gave the drawings to our engineering manager to have updated. They sat on his desk for over a fortnight. So on my shift the machine packs up, and the fault is somewhere in the stuff I’d altered. Now I have a good(ish) memory, but I can’t remember everything I’ve altered. I was having to do the hand over hand method of following each line. I’d all ready done the usual “that can be dodgy” bit and drawn a blank.

Enter the production manager in Attila the Hun mode. “Where the hell are the drawings?” I told him, not 10 minutes he returned with my original drawings. Fault sorted we walked back towards the workshop. As we passed the office block he asked me to go in to the offices. I was sat on the floor howling with laughter, tears rolling down my face. He’d only taken a sledgehammer to the engineering managers door to get to the drawing for me.

Strange thing is, when I returned the next night there was three full sets of drawings waiting for me. My spy in the management morning meeting reported back that the engineering manager was squirming as two of the directors laid in to him. It was only a minor breakdown but it cost about £36K in production.

 

[johnboy6083]

talking of drawings, im currently doing an evening class in CAD, and have 2006 at home. Does anybody have the electrical add ins, or a site where i can get them?

 

[fancypantsyeah]

can i just start by saying that when you are an apprentice that you are only as good as the people that train you ,,, you can only learn so much at college or tech the rest is learn or not learned on the job..... Employers need to invest more time and money into proper training of there apprentices.....

 

[UNG]

can i just start by saying that when you are an apprentice that you are only as good as the people that train you ,,, you can only learn so much at college or tech the rest is learn or not learned on the job..... Employers need to invest more time and money into proper training of there apprentices.....

The apprentices need to invest some of their own time as well, I don't believe that everything must be put on a plate and it's some one else's fault that education is lacking. It is easier to nurture apprentices with the right attitude than force feed the disinterested ones.

This is a side of the industry that to a lot is gobbledegook but being able to read drawings and schematics can save a lot of downtime it is too easy now to connect a laptop and expect it to lead you to the fault or reset the faults and wait for it to occur again.

 

[Knobhead]

There’s two sides to every coin.
How many put the effort in to learn how to read a drawing? It would seem now it’s something that doesn’t add to getting your precious bit of paper at collage so not important. Let loose in the big bad world of industrial electrical it’s what keeps you afloat. In the middle of the night you have a lifeline in the drawings, if you can read them.
I’ve been lumbered with more than my fair share of those who can’t. I’m not just referring to ex apprentices, I’ve had university graduates and time served tradesmen lost on some of the most basic things.

One thing I will add, to understand a drawing you need to know the production process. If you don’t know what a machine is supposed to do you don’t stand a chance.

 

[Knobhead]

Blast UNG beat me to it!

 

[Engineer54]

Nice one vaughant. I’ll be honest I don’t like modern A4 drawings where your jumping from page to page, I’d much rather have a big A0 sheet. But that’s my personal choice. As for teaching apprentices there have been times when I’ve been near to throttling them.
Us oldies can be as bad, (not me) the number of times I’ve had the same situation as you. Well we changed that, but it still didn’t work. “How far have you got through the sequence.” They hadn’t even got the drawings out! Just jumping from one guess to the next.

My idea of a drawing.
View attachment 11236
It’s for an auto close OCB. Bits of it may look a bit weird as there’s a lot of CT’s used which are referenced to earth.

Like you Tony, i dislike the A4 format for schematic drawings that can be 30 sheets or more in a book format. You are literary sent all over these 30 sheets tracing out a particular line...
I was trained using full format drawings on a roll, unseen these day's but you could see where you were going, and the the overall picture most of the time.

I would hate to think how many A4 books of schematic sheets you would need on some of the panels i used to work on!!! Eg, ....Think of a panel 12m long 2 m high and absolutely packed solid full of relay's, most of them being latch/unlatch relays along with contactors and god knows what else. ..lol!! The schematic drawings for this panel was on a full size drawing roll with 14 or more sheets, one drawing for each panel cubicle, and 2 or more sheets with external sections where the controls integrated with other control panels!!! lol!!

To be honest, i can't remember being taught how to read schematic drawings at collage, maybe some very basic stuff, but that was about all. All my training on this side of our industry, was given by the companies own training school/collage by lecturers that knew there business, many being retired foreman from the shop floor maintenance sections. And of course, on the job training, with experienced maintenance electricians.

Even with all the training we were given, the were always those that just couldn't grasp the full potential of fault finding with the aid of schematic drawings, they got by, but only just!! lol!!!

Reviewing control panel schematic drawings using these German style A4 sheets is a nightmare for me these days, flicking backwards and forwards between sheets. ...lol!!