Electrical Theory Myths

Bob from East Longmeadow Diagnostician Posted   Latest   Edited  
Discussion
Electrical
Myths

Ok, I'll take a stab at some myth busting. I'll post what I think I know and why and see what you all think.

Electrical theory Myths 

Electricity always goes to ground AND Current takes the path of least resistance 

I'm doing these together because they are somewhat related to each other. I would guess that most of us in this industry have heard these statements or variations of them over the years. Whether at training seminars or in training material, these terms were frequently used even though they are misleading. 

Lets take the first one, "Electricity always goes to ground". 

I believe it's always been taught this way in our industry because the battery negative is connected to "chassis ground" and many components will have their negative connections going to sheet metal somewhere, or as referred to in the service information, "ground". In fact, many euro manuals will refer to this connection as "earth ground". 

This can be confusing because when things are connected to the actual earth it's often assumed that the electricity terminates in the ground but this is incorrect.

A much more accurate way to view this is to understand that current ALWAYS RETURNS to the source. It doesn't "go to ground" it takes whatever path needed to RETURN to the source. Ground is not a termination point, it's a path back to the original voltage source and the current WILL return to the source as long as there is a complete circuit. Ground in an automobile is simply a common return path for the current to return to the source. 

This brings me to the second Myth, "Current takes the path of least resistance".

Again, this is fundamentally misleading because it gives the impression that ALL the current will take the path that has the least resistance. If this were the case, parallel circuits with different resistances wouldn't work. If current simply takes the path of least resistance, then the only leg of the parallel circuit that would work would be the one with the lowest resistance.

A more accurate way to view this is that CURRENT will take ALL possible paths in a circuit. The current that flows in each path will be determined by it's resistance according to ohms law. Now, although the path with the least resistance will carry the highest current, any other available paths will still flow current. 

Now here is an example of how these two electrical fundamentals are related. I'm sure we have all had a a vehicle with a strange symptom where activating an accessory or stepping on the brake etc. causes some strange unintended circuit behavior. More often than not the root cause of the problem will turn out to be a bad ground. Why? Because when power is supplied to a given circuit it wants to flow through the load and then return to the source. If the designed ground path is not available, the current will take any other path available, even if it's through another component. How it happens specifically will be determined by the paths available and their specific resistances. But make no mistake, the current will return to the source if a path is available and it will take ALL paths available. The effect on the system will be determined by each paths resistance and components.

These two electrical theories have been kicking around in my brain for most of my career. I have heard them stated many times over the years but never really dissected their true meaning. I will say that although many of the top tier instructors in our industry today do a much better job of explaining concepts like this, the training that had the biggest impact on me regarding these principles actually came from the electrical industry.

Ironically, the training was targeted to electricians who are studying the NEC or National Electrical Code however, much of the fundamentals discussed are also relevant and related to our field, especially with the rise of electric and hybrid cars which utilize AC and DC power circuits. 

I will finish with a link to one of the training videos I watched that was extremely eye opening for me. It is hosted by a man named Mike Holt who is one of the leading experts and trainers in the electrical industry. As an added bonus in viewing this training, I also learned a tremendous amount about electricity generation and concepts of grounding and bonding that protect electrical equipment and make it safe for people. It's an hour well spent. 

youtube​.​com/watch?v=mpgAVE…

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John from Beaver

 

Instructor
 

OK so while you are pondering these questions, try this one.

You wrote "This can be confusing because when things are connected to the actual earth it's often assumed that the electricity terminates in the ground but this is incorrect. A much more accurate way to view this is to understand that current ALWAYS RETURNS to the source. It doesn't "go to ground" it takes whatever path needed to RETURN to the source. "

Try to answer the questions written on this little drawing that I made and see if they agree or disagree with your above statement.

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Bob from East Longmeadow

 

Diagnostician
 

Will current flow when the magnet is moved? Yes

Is this a complete circuit? Depends

If we are talking about a DC circuit then no. However, you have introduced the principles of magnetic induction. That is straying a bit from my my two fundamental ideas. 

I'm not sure what point you are trying to make? 

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John from Beaver

 

Instructor
 

That the traditional way we teach electronics only covers part of what techs really need to know. That's why they don't learn why certain beliefs are false. It also explains why they can get lost from time to time when attempting to figure out a given circuit.

In the last post I asked if that was a complete circuit and "depends" isn't a good answer because we routinely teach that current can only flow in a complete circuit and yet current can be made to flow in that circuit. I made a little change and added an LED and now only have the magnet moving one direction. This example forces us to ask more questions and also have to add in instantaneous values and not just ones that can be seen over an extended period of time. Would the LED light up if enough potential was produced? What if the magnet was moved in the opposite direction. What if it was reversed and used the negative pole instead?

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Bob from East Longmeadow

 

Diagnostician
 

Even though current can be made to flow in your wire with the magnet, I don't think it represents what we would commonly understand to be a complete circuit. 

My comments and examples were focused on traditional automotive DC circuits. I think it gets a lot more complicated when you start adding in magnetic induction principles.

I think it would be possible to light the led with enough magnetic induction and the right polarity but I'm by no means an expert in this area so I would love to get your explanation of your circuit and the principles it functions by.

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John from Beaver

 

Instructor
 

Of course it doesn't represent what we traditionally think of as a complete circuit, but it is a circuit none the less and the next thing that comes into reach from it is why techs need to wear a grounding bracelet when working on today's sensitive electronics. The static charge build up doesn't need to have a "return" path in order to have a current flow into a component and potentially damage it. You started off stating that "Electrical theory Myths ….Electricity always goes to ground AND Current takes the path of least resistance" and a little later came this line "A much more accurate way to view this is to understand that current ALWAYS RETURNS to the source." Except when it doesn't.

My only point is that we need to go further than just the basics when it comes to electronics.

I'll save the whole explanation for another time but I'll throw you something to dwell on, and that is the word "wave".

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