Susan Brown

[Susan Brown]

In a *functioning* 120v circuit, with one load, you will have line (hot) on one side of the load, and neutral (ground potential) on the other. So when you are measuring for voltage drop, you will put your probes on either side of the load (or EEPs corresponding to either side of the load) and see if you get voltage. If current is flowing through that load, you will measure a voltage drop, which should equal the source voltage (because we’re talking about a circuit with one load).

If current is not flowing through the circuit, because it is open somewhere, then you will either not have line or neutral present at the load. In either event, you would measure 0v across the load because you would be actually measuring line wrt line, or neutral wrt neutral, depending on which side of the circuit is open. In this case, you could then do a measurement of voltage with one probe at one side of the load, and one probe on a known-good neutral. If you get line voltage here, then you know the open has to be on the neutral side of the circuit, because we only get voltage from the line, or hot, side of the circuit.

If you have a 240v circuit, these things are a little different. Do you remember Question 9 on the Midterm exam where we had to disconnect one side of the circuit so we could figure out which side was open?

Does this help?

[Susan Brown]

Hi Jon,

It’s good to be thinking through these things!

In the first instance, with the light off, you were measuring the voltage potential at the outlet.

In the second, with the light on, you were measuring the voltage drop across the load (the light).

You are correct that if you measure across a closed switch you would expect to measure 0v, but you didn’t have your probes just on either side of the switch – you had them on either side of the working part of the circuit – the light bulb.

Does that make sense?

[Susan Brown]

Thanks! I just added an exception to that “Pro-tip” (if the valve has a removable plastic filter, you can clean or replace that)

[Susan Brown]

They do, but one half of it can trip without tripping the other side. We aren’t saying it happens a lot, but it is common enough that you always want a customer to check it if they report certain things.

[Susan Brown]

240v appliances experience all the same types of problems as a 120v appliance (failed loads, switches, or boards), but a unique issue that can happen is that one of the breakers will trip and the appliance will only receive 120 V AC. A classic example is when an electric dryer will tumble but have no heat.

[Susan Brown]

My first suggestion is that you rewatch the AC Voltage measurement video in Mod. 4, unit 7.
https://my.mastersamuraitech.com/module-4/basic-electricity-electrical-measurements-in-appliance-repair/

And also read the section further down in that unit about Loading meters.

The point of a loading meter is to allow more current to flow in the circuit to eliminate the possibility that you are reading “ghost” voltage.

Do you recall where that video is that you are referring to?

[Susan Brown]

Correct.

[Susan Brown]

Hi Tracy, you are on the right track. Main coil is shunted by the closed switch, so 0v.
The Safety is easy to see – it is an independent circuit with one load, in *parallel* with the others, so 120v.

The Ignitor and the Booster are in parallel – why would they split up the voltage?

[Susan Brown]

What a coincidence – I was just asking the Samurai this question myself yesterday!

It is definitely not neutral, neither is it line voltage. But it is “hot”. In other words, you would measure some voltage in between the two loads (with respect to neutral).

As an example, if the two loads had the same resistance, then you would measure 60v wrt N in between the loads, because each one would drop 60v.

Make sense?

[Susan Brown]

Hi Anthony,
Just to make sure we understand your question – are you asking if the explanation (“Both the main and sub PCBs would be replaced because 1) the Fast Track says to replace the PCB *assembly* which means BOTH boards, if they meant just the main PCB, they would have said that”) comes from somewhere on the Fast Track, or just from our general knowledge of these things?

[Susan Brown]

Hi Mitchell,

Most of our videos are hosted on Vimeo, but a few, like these, are YouTube videos. They work fine for me right now, so I assume you were having some temporary issue with those.

See the Video Playback section on this page for more suggestions to try, if they still aren’t playing for you.

https://my.mastersamuraitech.com/appliance-repair-course-support/student-resource-page/#video-playback

Let me know if you continue to have this issue, and I’ll make sure you get the video links another way.

[Susan Brown]

Yes, 2 is the correct answer. It is great to see you working on understanding the questions you missed, even though you “passed.” Not all students do that.

[Susan Brown]

Hi Michael,
Questions like that you can always email me about, FYI. But this is fine, too!

MST Courses are like parallel circuits – what happens in one does not affect the others 😀

The only thing you risk by taking a break is needing to spend more time refreshing for the Final Exam. However – that is actually a better method in terms of retaining the info. And hopefully you’ve been taking good notes to help you with this.

[Susan Brown]

Hi Dylan,

I’ll start by just telling you how I came to understand it, to see if it helps.

All voltage is a difference in charge between two points. For our purposes (dealing with circuits in appliances), there are two categories of voltage.

1. Voltage potential – the difference in charge between two points where there is no current flowing, but there is the potential for current to flow if there is a closed circuit between those two points. A common measurement of this type of voltage is putting one probe at one side of a load, and the other at a good neutral point. Or, measuring across an open switch.

2. Voltage drop – the difference in charge from one side of a load to the other, created by current flowing through the load. In other words, you will only measure voltage drop in an active circuit.

“Dissipation” sounds more like an idea from power transmission, where you can have some losses due to small amounts of resistance over very long stretches of power lines. Small amounts of the power are transformed into heat and lost to the environment. This is not something we deal with in appliance circuits, which are very small compared to transmission lines.

Here’s something else to keep in mind. In circuits, there are always two sides to every power supply. Either L and N, or L1 and L2. These two sides meet at loads.

Switches, on the other hand, are always on just one side of the power supply (otherwise they would create a short).

Let me know if this helps, or if you have any follow up questions.

• This reply was modified 11 months, 1 week ago by Susan Brown.

[Susan Brown]

Hi Douglas,

That is correct. The closed detector switch is a [answer hidden]
Good job!
Note – I will need to hide these answers.

• This reply was modified 11 months, 1 week ago by Susan Brown.

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