Schematic Guidance

J

jdawson

New User
Location
Anaheim, CA
Occupation
Electrical Engineer I
Howdy all,

I graduated in May with a BSEE. I've recently got a job for a company that manufactures devices controlled by PLCs. Mostly just simple (on/off) fan motor control, light control, E-stops, button control, the odd sensor.

As far as I know I'm the only BSEE employed by the company. My boss and all of my coworkers are mechanicals. My predecessor was too, although more electrically inclined than some. Early on in my onboarding I was told by some of my coworkers to not take anything I learn here as the... right, or standard way to do things, compared to other companies.

Most of what I've been doing in the last few weeks has been rubber stamping schematics before production. Yeah, this product has slightly different outside dimensions but identical electrical components? Copy-paste the schematic from an old model, tag it with the new serial, ship it.

Now though, they're having me select components and design a control box for a new product. I need to draw the schematic for this.

I'm looking for good examples of drawn schematics of industrial control panels that I can compare my own drawings to. I'm also looking for general advice. Power Systems was one class two years ago and I had never touched a codebook until I started this job.

jdawson
 
If your are building control panels that will be Listed to standards like UL508A, then NFPA70, the NEC, will not help you as much as NFPA79, the standard for industrial machinery.

Neither of them contain much in the way of standards for schematics. You might want to look at some wiring diagrams from companies like Rockwell, or Schneider Electric. They used to have booklets for common starters and such.
 
First off, congrats on graduating and welcome to the field! My second job (~25 years ago) sounds a lot like what you're getting into, only that I was trying to break another programmer's logic in new and creative ways and writing some relatively simple PLC automation of my own.

As Jim says, you'll not find a whole lot in how to create schematics in the various codes and standards; those are going to tell you "For situation A, THHN is an acceptable wire type, SJ is not. Running through environment R requires EMT rather than LFMC. Emergency egress lighting requires N minutes of battery," and stuff like that. Companies will have their own methods for creating schematics (the one I was at just doodled with MS-Paint on WinXP, they were too small to afford AutoCAD), but symbols for things like fuses, motors, relays, and the like will be common among all, so make sure to learn those. On the plus side, it sounds like you'll be the one creating your company's standards, so the field's wide open when it comes to choosing what tools to use. If your designs are relatively simple and very cookie-cutter, Visio might be enough to get the job done. If you're getting into really crazy complex stuff, it might be worth looking into an AutoCAD subscription.
 
At one time mfgs had catalogs that had all sorts of wiring diagrams to pick & choose from.

I used The Constructor from CMH software to draw my own. Diagrams could be run in a simulation mode to prove operation.
AD also has PLC and HMI software that can be simulated. I would expect others to have similar.
 
jim dungar said:
the NEC, will not help you as much as NFPA79, the standard for industrial machinery.
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I'll give it a read then, thanks. They are going to have me submit stuff to UL later but I figure that's a question for them and their book.
ModbusMan said:
Companies will have their own methods for creating schematics
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That kinda answers my main question. I was worried there was some standard.
ptonsparky said:
I used The Constructor from CMH software to draw my own.
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This looks pretty cool, thanks, I'll have to mess around with the trial.
 
jdawson said:
Now though, they're having me select components and design a control box for a new product. I need to draw the schematic for this.

I'm looking for good examples of drawn schematics of industrial control panels that I can compare my own drawings to. I'm also looking for general advice. Power Systems was one class two years ago and I had never touched a codebook until I started this job.
Click to expand...

"In general", to facilitate reading, schematics should "flow" from top to bottom and left to right.

Connections should always be T's, not X's -- this makes it easy to decide if those two crossing signals are connected, or not (they aren't, even if a "big black dot" was present -- but didn't photocopy correctly!)

Avoid using color to convey information -- 15% of men are colorblind. And, reproductions often are monochrome.

Avoid using 0 and O in the same class of identifiers (likewise 1, l, I, B, 8, etc.). Remember that the copy that someone else references will not be of the same vintage as the original that you create!

Some industries like to use schematic symbols that are representative of the actual devices being used (barrier strips, etc.). Others want some level of abstraction based on appropriate "standards" (even if they are only informal).

Ask yourself if YOU can read (and comprehend) what you've created 2 years from now -- you may have to!
 
Ynibe said:
Avoid using 0 and O in the same class of identifiers (likewise 1, l, I, B, 8, etc.). Remember that the copy that someone else references will not be of the same vintage as the original that you create!
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Good advice here... waaaaayyyy back at my very first job out of undergrad, I worked at a company that intentionally jumped over the letters I and O in their production-level document revision sequence (which used letters) to prevent accidental confusion with design/prototype revisions (which used numbers).
 
ModbusMan said:
Good advice here... waaaaayyyy back at my very first job out of undergrad, I worked at a company that intentionally jumped over the letters I and O in their production-level document revision sequence (which used letters) to prevent accidental confusion with design/prototype revisions (which used numbers).
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You have to consider that the schematic is your "product". Your customers are the people who will eventually read it. They will likely most be interested in how clearly and concisely you manage to convey the necessary information as that will impact the ease and accuracy of their work.

Anything you can do to reduce the effort required for them to understand the intent of the document is a win.

As a side note, I was always amused that telephone dials (dials? what are those???) did not omit I ("I") and O ("6") in the alphabetic assignments. Nowadays, folks only use the letters to dial vanity numbers like "1 800 BUY THIS". But, ages ago, it was common for numbers to be expressed as a combination of letters and digits like "SImple 90123" for 749-0123 (of course, exchanges weren't allowed to have a 0 or 1 in the initial or middle position so the 'I' in SImple could never have been seen as a '1')

And, that 'O' could so easily be misinterpreted as Operator.
 
jdawson said:
That kinda answers my main question. I was worried there was some standard.
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I think there may be several standards, but you are probably not required to use any of them.

NECA 100-2013 seems to be available as a free PDF just by searching for it by title.

NEMA ICS 19-2002 is another one, and the IEC also has a standard. (It looks like NEMA is the ANSI standard, and the IEC is the ISO standard. )

I also have a Square D wiring diagrams book that I sometimes refer to . There is a PDF here:

www.scribd.com

Square D Wiring Diagram Book | PDF | Switch | Relay

Electrical equipment should be serviced only by qualified electrical maintenance personnel. This document should not be viewed as sufficient instruction for those who are not otherwise qualified to operate, service or maintain the equipment discussed. No responsibility is assumed by Square D for...
www.scribd.com www.scribd.com
 
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