Here is a question to make you think.

How much electrical theory should a first year apprentice know?

Not so much on the job stuff but classroom work.
Now that I am in a teaching post I am having to re-learn a lot of stuff. Stuff that I just took for granted whilst on the tools (never looked at once on the tools more like, or just did without thinking about it)

I have been asked to look at the units I teach with a view to improving them. Ohms law , Kirchofs law, series and parralel circits are quite staight foward. But the only way I see of taking these units froward is to introduce more AC theory.
Is it usefull to know how to calculate RMS, peak and average voltages,complex numbers, phase angles and the like?
Shurely only a systems designer is concened about these calculations? Or do you use them out in the field?????

Kenbo:
I also teach. County Vo-Tech, evenings,
Basic Electricity and/or Basic Wiring

Start off with Ohms Law & theory, and dependent on the 'level' of the class; I may switch quickly into the DC to AC.

I have to go from basically Page 1 of the subject book; but I have options to improvise as needed.

Depending on the levels of the class, it may be 3-4 nites on series for instance, or it may be 1-1 1/2 the on to parallel.

IMHO, if they learn the basic theory (& formulas) and know where to look for it IF they ever need it (DC) then they will be OK

John

from a contractors perspective, save the theory for a bit. 1st half of 1st year should be practical. Nothing fancy, just wire sizes and ampacitys (upto #8 or so) basic principals of distribution, some notion of different receptacles and what they are for.

I say this, because we hire 1st yrs who don't know the basics, so we have to spend time teaching them. costing the contractor money. But at the same time they are getting seriously confused by all the theory that they are learning in school.

once we spend 6-8 months teaching them the basics everyday, then they seem to grasp the theory better.

it's a tough call, and this is just from my experience.

The NCCER has designed a non-union apprenticeship program for electricians. Their texts -one for each year- are available through Prentice-Hall. That said, look at page 25 of this:
http://www.prenhall.com/crafttraining/catalog.pdf

This page of their catalog give an outline of their program. "Level 1" is year 1, and each "module" is a chapter of the book. That ought to give you some ideas for systematically teaching apprentices.

Beyond the basic physics of how many amperes you can stuff into a given size wire, one of the basic tools that apprentices can utilize early on is transformer thoery. Perhaps an overview of the Tesla System, briefly how it is made, distributed and down to the level that we work on every day, how the basic 120/240 voltage is derived, 120/208 and 277/480, but start with a basic doorbell circuit and turns ratio=voltage ratio stuff. Kirchoff's Laws are a bit esoteric for a beginner, they can't relate, whereas the question of how come a house has x voltage between this drill case and the water pipe I just grabbed is something every greenhorn can relate to.

Ohm and Kirchoff are important but mostly from the overview aspect.
Ohm says the current is dependent of voltage and resistance, an important concept to understand.
Kirchoff says if the current went in there it is all coming out somewhere, also important.

As far as school goes, I got just basics when I started out. I learned quickly in the US Navy and parlayed what I learned there into wiring new homes. Out in the field nobody teached me any theory. Somehow I managed to survive and before too long I was wiring all sorts of things including services.

I'm in school now learning all about theory and I have a new found confidence in the workplace because of it. I should've done this 10 years ago!!!

As fas as being out in the field, I am teaching a 1st year guy who knew nothing 6 months ago. One of the first things I taught him was how to avoid being shocked. That means never working live unless you really have to. But he understands about becoming "part of the path" and the measure that need to be taken to avoid accidential shock. He can cut-in and wire receptacles, single pole switches, sometimes even 3-ways, and understands the importance of using GFCI protection on construction sites.

[This message has been edited by ShockMe77 (edited 10-09-2006).]

While theory is fine - and I certainly appreciate the need to understand why you need to do things a certain way- I fear that we have a tendency to give too much theory too soon.

I think that first you need to learn what gets done. Then you learn how to do it. THEN you learn the 'why.' When all this is covered, then you can begin to tinker with things, try to apply what you've learned.

Instead, I have been in far too many coures where they started off with theory. Ask "how," and the response was "you can figure it out."

Even in our trade, I have encountered far too many who spoke knowingly of "harmonics" - folks who had never seen an amp clamp. had no idea how to use one, or any clue as to how to identify / eliminate harmonics as the problem. To me, this is a sign of when "education" has exceeded "learning."

One aspect that complicates things is that many come to the trade having already been mis-educated by their prior jobs. I suspect that most of the first year is spent 'un-learning' bad habits.

I would say a mixture of both for the first years. Therory in itself wont tell you how to actually put it together, but all the machnical ability in the world wont give you a clue to how it actually works. I would say a delicate balance of hands on, and know how and know why. If you hold off all the book work, it will never get done, but if you drown them in it, they are useless for a few years in the field.

Is the book end of it usefull? - darned straight it is! If you have no understanding of therory, you are essentially a Parrot - mimicing what you have little understanding of. Doing what you are told.... You might be able to connect 2 wires together but not be able to understand how or why to fix something, and will have a really hard time troubleshooting later, if at all. And all circuit design is in the field. No one has ever handed me a schematic or line drawing of any use.

Conversely, I learned therory, and was trained to troubleshoot before I got out of the classroom. I could troubleshoot generators from the engine through the voltage regulator and through just about any 3-phase motor control you threw at me. But ask me to actually install something and I was clueless.

The "laws" are useless without therory, and practical application can be a life of robot work without a fuller backround of understanding.

However, therory at this level does not need to be complicated. It can be summed up in some simple anaolgies. It doesn't need to broken down to the atomic level to gain an understanding of Ohm's law, or visualizing a sine wave, or understand the difference between AC or DC. The Firehose, Ping-pong ball, Billiard ball or Pachinko game anology would work fine for the purpose.

The ping-pong ball theory?

The water-flow analogies were very helpful for me.

Theory - to what level is a good reality for 1st year persons?

I would think these people should be given more practical theory examples, and leave the advanced stuff for 2nd, 3rd and 4th year persons.

Basic Circuitry is a must! Understanding how to figure Series, Parallel and Combination Circuits + calculate the results is needed from the start.
Along with this, some rudimentary current flow concepts are necessary. Something which describes DC flows and AC flows - yet remains simple enough to understand by entry level persons.
This will assist with connecting AC equipment to Grounded + Ungrounded Multiwire and Polyphase circuits.

A little crash course on Pythagorian Theorems, so they get a glimpse on how Power Factors + Impedances are figured.

Push details on basic of:
* Transformer connections and sizing,
* Motor connections and circuitry,
* Lighting equipment and circuitry,
* Service equipment and related circuitry,
* Panelboards, Feeders, and related figures,
* General Power-Related loads, figures and circuitry (receptacle circuits, etc.),
* HVAC circuits and figures.

Within these areas, the principles of Code-Compliancy, LCL, Planset layout, and the like may be covered enough to give the entry-level persons the insight they really need for the field.

Good luck with your lesson plans!

It's great that you are seeking input like this, in order to give your students the best lessons!
Definitely keep up the great work!!!

Scott35

Yep, ping-pong balls!

Take a dozen or so ping-pong balls - Put them in a clear plastic tube. (A flouresant bulb guard will work) Cap both ends. Allow the balls to have enough room to roll back and forth inside.

Then describe AC generation:

• Electromagnetism pulling one way - Gently tilt the tube one way. Electrons pulled one way.
• Electromagnetism pulling the other way - Gently tilt the tube the other way. Electrons pulled the other way.
• Demonstrate resistance of a load by giving the tube a gentle squeeze in the middle so the balls slow down as they pass slowly back and forth.
• Demonstrate a short by un-capping one end and send them flying all over the room at high speed.

Yes, I just made this up, but an apt analogy. You could use anything....

Scott you got in there before me....

Anyway, before attempting any "serious" therory, some good visual aids are good for basic understanding of the general concept. Bury people in valence rings and high math, you just might get them lost.


[This message has been edited by e57 (edited 10-10-2006).]

Thanks for all the replies. You have given me a lot to think about.

Hotline.... these are the units I teach as they exist the now. I have to wright all the course work my self.
D9AF 11 40 Hours
D9AG 11 40 Hours
D9AH 11 40 Hours

Reno... thanks for that just tying in that link with my units and compairing the two

mahlere.... appriciate your point it is a fine point getting the ballance between theory and practical just right.

e57.... Ping pong balls I use marbles to show current flow. "Glass tube full of marbles represents a wire full of electrons. Add one marble to one end and one pops out the other end instantously no matter how long the tube is."

Kenny

Scott... sorry mate nearly missed your reply there

I am considering adding a new unit covering, inductor-capacitance, motors, power factors but wonder of their relivance to apprentices at this level.

Thinking back to my apprenticeship I learned all these things but then never used the theory out in the field....

So thinking about it, my real question should be are these subjects relevent to learn in any depth, or should they have an awairness, that can then be further developed in their carrear is they so choose to do so.

Kenny

I'd suggest covering 3-phase power as well. This is a tough nut for a lot of people to wrap their heads around in the field, and is much better suited for the classroom. I honestly don't know why this isn't covered more in school- they don't even teach it to electrical engineers in college outside of specialized elective courses few EEs take. A solid understanding on delta and wye 3-phase power in the classroom and a few exercises drilling 1.73 into their heads will go a VERY long way in the field.

I'd recommend awareness of inductors and capacitors restricted to general understanding of what they do to AC circuits as opposed to mathematical equations (the complex phasor mathematics required for any sort of depth is likely beyond their mathematical background anyhow), but I would recommend some depth on PF and how to translate kW to kVA, and maybe some examples relating this to meter readings they may be taking in the field, as opposed to the typical classroom study that has you calculating PF based on the different parts of the circuit.

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[This message has been edited by SteveFehr (edited 10-10-2006).]

[This message has been edited by SteveFehr (edited 10-10-2006).]

I made up a demonstration of motor theory for the middle school that was pretty well received. I had a bunch of small bar magnets with a hole drilled through the center (from a matrix print head). I identified the north and south poles with red/green paint. I strung some on brazing rod in different orientations to show attract and repel.
Then I wound an electromagnet on a steel spool with bi-color LEDs across it at the ends. Hooked up one way the LED on one end was red, the other green corresponding to north/south, swap leads to the coil and it swapped colors. That was next to more magnets on rods that repelled and attracted. The last step was a hand wound St Louis motor (permanent magnet DC motor) It also had the same deal with the LEDS on the rotor, wound on the same spools. The comutator was a chunk of .45 brass cut in half and epoxied to the shaft, brushes were springy brass. When you ran the motor you could see which way the rotor was conducting by the color of the LEDs. It really looked pretty cool when it was running. They set it up as a demo at the regional science fair but I wasn't elgible for a prize