Susan Brown

[Susan Brown]

Okay, I’m glad it is working. Usually, when videos aren’t playing, it’s an isolated problem with the student’s system or connection.

[Susan Brown]

By the way – very good question to ask! It shows you’re really thinking about this stuff.

[Susan Brown]

Sorry about that! I must have read your question too quickly.

If the door switch were open, then neutral would not be present at the push to start switch, and we would not expect to get the readings that we did.

[Susan Brown]

Hi Jessica,

Great question – this is good material to think through.

When a switch is open, you expect to measure voltage (potential) across it. In a 120v circuit, there is “line” voltage on one side, coming from L1 in the power supply, and neutral on the other side, coming from N at the power supply. So when you measure the voltage from one side of the switch to the other, you measure 120v (the difference between L1 (120v) and N (0v)). It is “potential” because current is not flowing. We have the potential for current to flow, because voltage is present. We just need the circuit to close.

When a switch closes, it then allows current to pass through it, and it acts like a wire. A wire does not have a voltage difference across it. The switch is no longer open to create a voltage difference. The voltage difference will then occur across the load (or loads) in the circuit – we call this difference voltage *drop* (as opposed to potential). We’ll be talking more about voltage drop in Unit 8.

So when he presses the button and the voltage goes to 0v, he knows the switch closed as it should.

Does that make sense? Don’t worry too much if it isn’t 100% clear to you yet – we’ll keep working on these concepts. But let me know if you have follow up questions.

[Susan Brown]

You are correct! I reset you.

[Susan Brown]

I think you have figured it out since you posted this – but just to make sure, did you see the explanation for this question?

Since the light stays on when the jumper is disconnected, the light must be getting L1 from some other source. Thus, we can conclude that H1 to L1 is not the problem.

[Susan Brown]

The only dopes are the ones who don’t ask questions when they are unsure of an answer!

“Step-by-step troubleshooting instructions” are not included on a tech sheet, although I’m sure many poorly-trained techs wish they were. There may be various amounts of guidance, but they do expect the tech to have a basic level of troubleshooting ability. Instead of that item, you should have chosen “the schematic”.

[Susan Brown]

Of your three answers for outputs, this one is wrong: “Motor speed feedback signal”

Outputs from a main control board are most often something to do with “power supply”

• This reply was modified 5 months, 3 weeks ago by Susan Brown.

[Susan Brown]

Hi Lukas,

Did you see this topic already?
https://my.mastersamuraitech.com/appliance-repair-course-support/student-forums/topic/module-5-unit-5-2/

[Susan Brown]

You have a membership at Appliantology – you can post in the Tech Forums, even if it is your own machine.

[Susan Brown]

It does take some time and practice, but you are on your way!

[Susan Brown]

Hi Andrea,

#5: The LOI *is* the “thing that ain’t doing its thing.” The LOI is NOT the component that you necessarily think is broken. If a motor isn’t running, it could be faulty, or perhaps it just isn’t receiving power due to a failed switch or board. But either way, it is the obvious item that is not functioning, and where you will start the Ten Step Tango.

#9:
They must be in continuity with each other
There must not be any voltage difference between them

[Susan Brown]

Ok, I think that makes sense.

It’s good that you are thinking this through and asking questions – keep it up! It takes time to really understand this stuff.

Am I right that the earth does not factor in with 240v? Because l1 and l2 complete the circuit?

Correct. Both L1 and L2 are “hot”, but out of phase with each other. Whenever L1 is +120v, L2 is -120v, and vice versa, so there is always a difference between them to drive current.

With Line-Neutral circuits, Line alternates between + and – 120v, while Neutral is always at 0v, which creates that voltage difference.

[Susan Brown]

Hi Clark,

You’re talking about this question, correct?

An AC circuit is properly grounded and supplied with One Million Volts. You are standing barefoot on ground and grab a hold of the bare neutral wire. What happens to you?

The correct answer is nothing.

Remember that voltage drives current. In an active 120v circuit, both sides will have current flowing, but only one side is “hot”. The hot (or “line”) side of a circuit is the side that has voltage. The neutral side is always at ground potential. There is at least one load in the circuit that divides line and neutral.

If you grab the neutral wire while standing on the earth barefoot, current will not flow through you because there is no potential difference between the neutral wire and the earth to push current through the resistance of your body.

If you were not grounded, or the neutral wire was not properly grounded, so that there was some voltage difference between the neutral wire and the surface you were standing on, then some amount of current would flow through you.

As for your last question, the neutral wire coming into the breaker box is tied to earth/ground. But that isn’t the same thing as completing the circuits within our home.

Pop quiz: Think about a 240v (L1-L2) circuit. Does the earth factor in there?

• This reply was modified 6 months, 1 week ago by Susan Brown.

[Susan Brown]

Timer contacts are a type of switch. Do you know what voltage you would expect to measure across a closed switch? (which acts just like a wire – no resistance)

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