Scott Brown

[Scott Brown]

Exactamundo! Very succinctly put. You have snatched the pebble from my hand!

Circuit configurations where one branch is a load and the other is simply a conductor are not, by definition, parallel circuits; they are a special class of circuit called either a short or a shunt (depending on the exact configuration).

[Scott Brown]

Hi Trevor,

I’ve had my terminal kit for years. I didn’t buy it as a kit but rather assembled it with terminals and connectors that I needed as I needed them.

You can buy a plastic organizer tray and the buy packs of different terminals at the hardware store to stock the compartments. You may even find a kit of assorted terminals for household use as a starter kit. Also check around Amazon, you may find a kit there.

[Scott Brown]

Hi George,

I’ve re-worded the question to make it more clear. Also, the explanation to the question answer is shown after the question is answered. Check it out and see let me know if that clears it up for you or not.

[Scott Brown]

So then what is the purpose of a neutral line on a 240V appliance? To serve a load in a circuit that only needs 120V?

Precisely. Even though an appliance has 240 vac loads, it will almost always have 120 vac loads, too– motors, lights, control boards, etc. These loads will be served by either L1 or L2 and Neutral.

The only reason Neutral is there is to provide the return path for these 120 vac loads.

[Scott Brown]

Alright, let’s start with an understanding of what the function of Neutral is. Its job is to complete the circuit back to the power supply so that electrons (current) can flow. This job is not exclusive to Neutral. L1 can serve as the return for L2 and L2 can serve as the return for L1.

Let’s look at a diagram for household power:

(larger image here)

L1 and L2 come off opposite ends of the transformer secondary winding that serves the house. They are 180 degrees out of phase with each other– if you look closely at the diagram, you’ll see that in the sine wave representation for each phase.

You may be asking, “Since L1 and L2 are of equal opposite polarity at any given moment in time, then why don’t they just cancel each other out?”

This is exactly what they do at the Neutral.

But not “end to end.” The way to see this is to look at it as an electron would look at it when L1 and L2 are each connected to a load (eg, heating element). When L1 is at peak positive (+120 vac) and L2 is at peak negative (-120 vac) does the electron see 0 vac across the load? No way! Electrons see a huge chasm of voltage difference– and remember, it’s that voltage difference that makes electrons flow away from the negative polarity and toward the positive polarity. So at the peak conditions just described, the TOTAL voltage “gap” between L1 and L2 the voltage span from +120 vac to -120 vac for a total of 240 vac. They don’t care that voltage is negative because it’s all about the relative potential difference (or gap) between two points. And at that point of peak L1 and peak L2, the gap between L1 and L2 is 240 vac.

This graph shows how L1 and L2 add together:

So at the moment that L2 is at peak negative 120 vac, it is driving electrons away and the electrons are seeing that huge positive 120 vac at L1 and rushing towards it. And then they rush the other way when the polairty reverses. This is how L1 and L2 can act as “neutral” (more properly stated as “returns”) for each other. So the circuit is completed without the neutral.

[Scott Brown]

Okay, good! In both electric dryers and ovens, the heating elements are supplied with 240 vac, one side gets L1 (120 vac) and other side gets L2 (120 vac). Neither are supplied with neutral– in both cases, the elements are supplied with only L1 and L2. And when L1 and L2 are both present at the element (assuming the element is good) the element get so hot that it glows orange. I’m sure you’ve seen this. Is this what you’re asking about- how L1 and L2 can add together making 240 vac and complete the circuit for each other?

[Scott Brown]

In 240VAC however, doesn’t L1 (120) + L2 (120) just essentially create an L3 (240v) and they still need that neutral line 0VAC WRT, to create the voltage differential and drive current flow? I dont see how simply doubling the voltage to 240 will create the voltage differential if there is no neutral to connect to.

Trevor, so I’ll know the frame of reference from which your asking this question and how best to answer it for you, please answer this question:

Have you ever worked on a heating problem in an electric dryer or an electric oven?

Please keep your answer brief and directly on point because I’m going somewhere with this.

[Scott Brown]

If I touch neutral with my bare hand and also touch a metal grounded object nothing happens… Is this because my body and ground are at the same voltage potential

This is the key concept to snatch from my hand right here. This ties in with another concept I preach: EEPs (Electrically Equivalent Points). These are points in a circuit that are electrically identical as far as electrons see them: same voltage (ie., no voltage drop between them) and are in electrical continuity with each other. Now, stick with me…

What causes current to flow? Put another way, what drives electrons from one point to another? I hope you’re saying a difference in voltage between those two points because you would be exactly right. This is why there is no flow of electrons between EEPs.

So, back to your quoted excerpt above, electrons do not flow through your body because, neutral and ground are at the same electrical potential, in other words, there is no voltage difference between neutral and ground with which to drive electrons through your body.

And when I touch L1 or L2 with my bare hand and a grounded metal object the voltage differential becomes 120VAC, I become neutral/ground wire as well as the load and my body starts to do work (melts/fry’s).

Mostly yes. Your body doesn’t become neutral/ground but it absolutely does become the load in this case and does the “work” you describe.

Now consider this:

Suppose you are suspended in midair in such a way that you are not touching anything. A plate with a charge of 120 vac (L1) is brought up into contact with your bare feet. What happens to you?

Answer: Nothing… yet since you are not in contact with anything else that can create a voltage difference to drive electrons through your body.

Suppose another plate at 120 vac (L1) is brought up and you press the palms of your hands into the plate. What happens to you?

Answer: Still nothing because both plates are EEPs and hence no voltage difference to drive electrons through your body.

Now suppose you still have your feet on the L1 plate, and a plate at 120 vac (L2) is brought up and you press the palms of your hands into the plate. What happens to you?

Answer: Since you now have L1 at your feet and L2 at your hands, you have a voltage difference of 240 vac across your body. Result: electrocution, deformity, disfigurement, permanent organ damage, soiling undergarments, death.

But now suppose instead of the L2 plate it is a plate at neutral potential that you press the palms of your hands into. What happens to you?

Answer: Now you have 120 vac across your body. Result: electrocution, deformity, disfigurement, permanent organ damage, soiling undergarments, death, albeit at a fractionally slower rate than in the example above because the current will be half that of the 240 vac voltage difference.

[Scott Brown]

Correct! 🙂

[Scott Brown]

By Jove, I think he’s got it! Exactly right, Trevor!

[Scott Brown]

Still unclear on the definition of polarity at this point.

Positive is positive, negative is negative. What’s not clear? I’m unclear on why you’re unclear!

So COMM ( or ground in DC) acts just like the neutral (in AC) in completing the circuit for DC circuits? Confusing…?

Yes. COMM or DC ground is the counterpart to neutral in AC circuits. Their function is the same: complete the circuit Back to the power supply. Not confusing at all, just part of electrical vocabulary. Learn it so you can start adding concepts around it.

Where does the term COMMON come from and why is it used instead of ground or neutral?

COMM, common, and DC ground are used interchangeably. The choice of which term depends on which school the engineer went to. True!

The term Neutral is reserved for AC.

Ground (AC) and Neutral are NOT interchangeable terms. They serve two different functions.

[Scott Brown]

Now think about what you just correctly described about current compared to how you described the current flow and tell me what’s wrong:

I’m assuming the path of current flows from the +13V J2-8 pin to the COMM J2-3 pin

[Scott Brown]

Trevor, remember the video in Unit 2 where I explained what current flow is and electrostatic repulsion and attraction? Referring to that video, what is current flow made of? The answer to this question is important because it affects the direction of current flow as you’ve suggested it.

COMM is short for COMMON. This is the DC ground.

The second part of your question belongs in Appliantology. But you would be better off clearing up misconceptions in the first part of your question.

[Scott Brown]

Whirlpool is famous for misnomers and, as you gain experience, you will learn to overlook them.

The Chinese programmers they hired to write the algorithm for the Jazz boards would have served the American tech community much better if they used the term “Closed” rather than “Short.”

A closed bimetal in normal use is not, in any sense of the word, a short condition.

[Scott Brown]

Bummer! But, on the bright side, you’ve found the Business Course here at the Samurai Tech Academy the community at Appliantology so you now have several powerful resources to connect with and help guide you in the many other decisions like this one that you will inevitably encounter as your operate your appliance repair business.

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