Susan Brown

[Susan Brown]

Hi Stephen,

If there were another resistor in the circuit, we’ll call it R2, in series with the parallel set and R1, it really doesn’t make it that much more complicated. The total resistance in the circuit would be R1 + Req + R2, and then current in the series portion would be It = E/Rt. Then the voltage drops for the loads would be E = I x R, etc., just like I show in the video.

Most of the time we’re going to be dealing with AC loads/circuits in appliances, but there are some DC applications.

Whether the circuit is AC or DC doesn’t change the basics of what I demonstrate in the video. Electrons “feel” the total resistance in circuits, and that (along with voltage) affects the rate of electron flow (current). And the rate of flow through each resistance will generate a voltage drop and power (work).

And, FYI, it’s not likely that you’ll need to do more complicated series-parallel calculations like I’m showing as part of doing appliance repair, but being able to follow these calculations and play around with different scenarios can give you a feel for the behavior of electricity in different configurations, which is important for being able to read schematic diagrams.

If you want to try adding a resistor as you described and assign it a resistance, then do some calculations, show me what you get and I’ll check your work!

[Susan Brown]

Hi Bryan,
On some old-school or low-end refrigerators you are often manually controlling the damper door. If you set the freezer to the absolute coldest setting, you can actually prevent the damper from letting in enough cold air to keep the fresh food compartment at the appropriate temperatures.

Does that help?

[Susan Brown]

This is from the lesson:

This ignitor is wired in series with the gas valve, meaning that current is flowing through both whenever the circuit is powered.

So – if the burner has a flame, the ignitor also still “on”.

That explanation is there because we changed the question a couple of years ago, so if someone came back to look over the results it might have looked confusing because they would see the new question but the old answer. Sorry for any confusion!

[Susan Brown]

Hi Lucas,

There are two ways that you can get a voltage difference in a circuit.

One is regular voltage (or voltage “potential”). This type of voltage is measured with your probes on two points that are not both on a circuit with current flowing through it.

Example 1: measuring across an open of some sort (for example, an open switch, or an element that failed open), and reading voltage “potential”. That would be Line on one side and Neutral on the other, in a 120v circuit, or L1 on one side and L2 on the other in a 240v circuit.

Example 2: you could be measuring voltage with one probe on a point in the circuit, and another probe on a known-good neutral somewhere. This would also be “potential”, because the two measurement points are not both on the same circuit with current flowing through. Some of the measurements in the video are done like this (L1 wrt N, for example).

Two: Voltage Drop, which is the difference in voltage across a load that occurs when current is flowing through it. In the video, when we measure across the element (L1 wrt L2) we are looking for voltage drop. The fact that we don’t get any indicates that there is no current flowing, which means the circuit must be open somewhere.

In a 120v, L1-N circuit, if you have 120v potential at the load, then you know that the L1 side cannot be open, because that’s where your hot voltage comes from. Neutral doesn’t supply any voltage.

But because both sides are supposed to be “hot” in a 240v circuit, you can’t tell which side is open until you disconnect one side and see what happens.

When there is an open fault in the circuit, no current is flowing, and the voltage that is coming from the power supply will be present in the circuit up to that open point. So, with the open on the L2 side somewhere, L1 is able to be present from the power supply and through the element (which just acts like a wire) up to the point where the open fault is.

When we disconnect L1 from the element, that prevents the L1 voltage from being present through the element, and thus we see the change in the L2 wrt N reading in Fig. 2.

Does that help? Maybe try drawing out the scenario on paper and see if that helps.

Let me know if you are still unsure.

[Susan Brown]

Hi Lucas,

I’m glad you asked!

An open switch has infinite resistance. Current will not flow across an open switch in a standard 120v or 240v circuit. (* See note below)

One of the challenges to understanding electricity is that we tend to picture electrical current like water flowing. Water is an independent substance that can run through pipes or in a river bed, etc. Electricity is different.

To put it simply, electric current is made up of electrons that are part of the material of the circuit itself. In a copper wire, voltage puts pressure on the electrons in the copper atoms so that they want to move. This movement is electrons hopping from one copper atom to the next. An open switch breaks this ability for the electrons to move. The electrons to the left of the open switch feel the pressure of L1 voltage, but they have no where to go. They are not going to jump through the gap to the other side.

Review the second video in Unit 2, What is Electricity? Current and Voltage.

*Note: with very high voltage and a very small gap, we can get electrons to jump across an opening. That’s what spark modules do.

Let me know if you have any other questions.

[Susan Brown]

Hi Blake,
You are actually at the “Module” exam for Basic Electricity. (The “Midterm” Exam in Mod. 5, unit 1).

The Module exams are always a random selection of questions from the Unit Quizzes, which is why we advise you to study those. In this case, there are 68 questions.

The comments you are talking about are for the Midterm Exam – there is a study sheet for that once you get to Mod. 5, unit 1.

[Susan Brown]

So close! No problem – I just gave you another attempt.

[Susan Brown]

Yes, you got it, Mark – good job!

(I’ll have to hide the answers above so we don’t just give it away to others)

[Susan Brown]

In this equation, E is the voltage dropped across the load in question. So, if there is more than one load, then you’ll need to figure out the voltage dropped across the load in question.

The other option is to find the current, I, then use P = I^2 x R

[Susan Brown]

Hi Denis,

We link to tools on this page:

https://mastersamuraitech.com/appliance-repair-tools-list/

We don’t have any links there for connectors. I’ll ask Scott to chime in with any good examples on Amazon.

[Susan Brown]

Hi Zach,

This is a great question for Appliantology! Have you activated your free 6-month Student Membership there yet? (If not, see the Appliantology 101 course, which you can reach from your My Courses page, specifically units 2 and 3.)

The Ask the Teacher Forum is for questions about the material in the course. For “real life” questions, please use the Appliance Repair Tech Forum at Appliantology.

[Susan Brown]

Voltage is a *relative* measurement. It is describing the difference in charge between two points. One of those points is often Neutral, which is at ground potential, which we designate as “0v”. It doesn’t really mean that there is no charge in the earth – we just call it Zero.

So, saying “there is no absolute 120volts out there somewhere” is an accurate statement.

Of the five statements we give you in this question, all are accurate except this one:
“There is no absolute 10 amps out there somewhere”
So that is the correct answer choice for this question.

[Susan Brown]

Unit 6 question 5: “The regulated pressure for natural gas appliances is”
Correct answer: “5-7 inches wc”

We mean coming from the meter.

As Sam said in the other thread about this, The exact pressures will vary a bit from manufacturer to manufacturer. What we gave in the unit was some general specs. The important takeaway for you is just that natural gas is used at lower pressures than LP.

[Susan Brown]

Hi Alexander – please see this thread – does that answer the question for you?

https://my.mastersamuraitech.com/appliance-repair-course-support/student-forums/topic/natural-gas-pressure/

[Susan Brown]

Hi Phillip – you did the right thing by submitting the reset request form. There can sometimes be a delay since one of us has to take care of it manually. You are all set now!

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