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Old 04-28-2018, 09:41 PM   #1
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Default Electrical 101 question..

I already know I'm going to get flamed and bashed for this question lol, but I got to just bight the bullet and ask!

So, lets say you have a 120v circuit that feeds some sort of appliance. Lets say you go up into a junction box up in the ceiling and break the neutral that is coming off that appliance, you will read 120 from the neutral to ground correct? Also you will read 0 from neutral to the hot correct?

The question I have, why DON'T you read 120 volts from neutral to ground when you have yet to break the neutral? That's what I don't understand. Because the flow of current and volts are equally spread throughout the hot and neutral, am I right? So... Why do you read 120v on the hot but not on the neutral when all the wires are made up correctly and no wires are cut or anything.
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Old 04-28-2018, 09:44 PM   #2
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Wait... I'm going to answer my own question I think? The neutral and ground are bonded together at the panel, so there would be no potential difference. I swear... It's when I ask the question and embarrass myself, that's when I have the AHAA! moment

Edit: Okay this is my real question. So why DON'T you read 0 from neutral to your hot when everything is made up correctly? Doesn't the volts and amps flow threw both, so wouldn't there be no potential difference when reading off your meter?

Last edited by JasonCo; 04-28-2018 at 09:52 PM.
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Old 04-28-2018, 10:05 PM   #3
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If the appliance has an open switch, the unconnected neutral is isolated and you'll get no reading from it to anything.

When you put the meter probes from hot to the isolated neutral, you effectively hot up the neutral and since it's an open circuit, there's no place for current to go.
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Old 04-29-2018, 07:29 AM   #4
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First off, you need to be specific, you are are asking very vague questions but I wiil try to answer.

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Originally Posted by JasonCo View Post
So, lets say you have a 120v circuit that feeds some sort of appliance. Lets say you go up into a junction box up in the ceiling and break the neutral that is coming off that appliance, you will read 120 from the neutral to ground correct? Also you will read 0 from neutral to the hot correct?
As you have it written, No.

The way I read this:

You have a junction box with a simple splice in it. The feed from the panel and the connection to the appliance are the only wires in this box. You broke the connection between the 2 neutrals that are nutted together, and you took your meter and connected it to the white wire that goes the appliance, and the other lead on the ground in the box.

No voltage will be on this wire unless the appliance is on. If the appliance is off, you will not have voltage on that wire. If you measure from the hot wires, which should still be connected, and ground, or from the hots to the neutral coming from the panel, you will get voltage..
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Old 04-29-2018, 08:57 AM   #5
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If the appliance is on, you will measure the drop of the appliance.

if you break the neutral while the appliance is on(could be just one 60W lightbulb) and measure across both neutrals with your meter you will measure the voltage drop of the appliance e.g. it will not be 120 it will be less because the appliance is acting as a resistor and dropping some of the voltage. All you need is a cutoff plug and jumper to test this out for yourself.

Also use the terms line side and load side to be more clear. Imagine if you break the neutral in the JB. You will have one neutral going straight back the panel(line side) and one going to the appliance(load side).

If you measured from the loadside neutral to the hot you would measure nothing as there is no complete path to the source(panel)
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Old 04-29-2018, 09:40 AM   #6
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Awesome, thanks for the replies! So lets say you have a spliced neutral up in the junction box. You break the splice. So if the appliance is on, it'll complete the circuit and there will be a flow of volts and amps. So on the line side to ground, you will read 120. Okay I got that! But, what if you make the neutral back up, why don't you read 120 from neutral to ground, or read any voltage at all? Whenever I put my meter up to a neutral, it reads 0 volts from neutral to ground. Also why don't I read 0 volts from neutral to the hot. The way I'm picturing it in my head, I thought that the volts and amps flow equally through the circuit, so it flows on the neutral and the hot.
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Old 04-29-2018, 10:19 AM   #7
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In a complete circuit the source voltage drops across the load. If you have an open neutral, the source voltage goes through the load but does not drop.

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Old 04-29-2018, 10:45 AM   #8
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Quote:
Originally Posted by JasonCo View Post
Awesome, thanks for the replies! So lets say you have a spliced neutral up in the junction box. You break the splice. So if the appliance is on, it'll complete the circuit and there will be a flow of volts and amps. So on the line side to ground, you will read 120. Okay I got that! But, what if you make the neutral back up, why don't you read 120 from neutral to ground, or read any voltage at all? Whenever I put my meter up to a neutral, it reads 0 volts from neutral to ground. Also why don't I read 0 volts from neutral to the hot. The way I'm picturing it in my head, I thought that the volts and amps flow equally through the circuit, so it flows on the neutral and the hot.
First off, only current(amperes, aka amps) flows in a circuit. Voltage doesn't flow, it's the force that pushes the current through the resistance in a circuit.

If you break the neutral in the JB with the appliance on you will read the voltage drop of the appliance(load) but hardly any current will flow because you now have 2 resistors in series the first one is the appliance and the second one is you're tester. They are in series, series resistors add together and since your tester has a huge resistance(the greater the resistance the lower the current) hardly any current will flow definitely not enough to run the appliance.
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Old 04-29-2018, 11:14 AM   #9
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Ah okay, so voltage is the force that helps push the current. Does the appliance create the amount of amps depending on the power and voltage? I assume based on ohms law.

Also, my journeyman taught me just last week about resistors and transformers and how meters and things like CT's will basically convert amps to a readable amount, that there are coils inside that act as a resistance? Thus will lower the amount of amperage based on how many coils there are. Anyways

But I'm still confused about why you wouldn't read 0 from neutral to your hot when everything is made up. If your voltage acts as a force and your amperage is flowing equally throughout the complete circuit, why would it not be the same as your hot? Why would you not read 120 from neutral to ground? This is what I'm super confused about now
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Old 04-29-2018, 12:37 PM   #10
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Ah okay, so voltage is the force that helps push the current. Does the appliance create the amount of amps depending on the power and voltage? I assume based on ohms law.
Yes, that is called the load. Load determines current flow.



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Why would you not read 120 from neutral to ground? This is what I'm super confused about now
Because they are electrically the same point. They are bonded together at the service panel.
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Old 04-29-2018, 01:35 PM   #11
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Yes, that is called the load. Load determines current flow.





Because they are electrically the same point. They are bonded together at the service panel.
Awesome, thank you! But this leads me into my last question. So I get why you would read 0 from neutral to ground, because there is no potential difference, they are bonded at the panel.

Okay, so why do you not read 0 volts from neutral to hot when your appliance is plugged in and your circuit is a complete circuit. Every time no matter the situation, I ALWAYS read 120 volts from neutral to hot assuming everything is wired correctly. Why is this?
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Old 04-29-2018, 02:44 PM   #12
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Okay, so why do you not read 0 volts from neutral to hot when your appliance is plugged in and your circuit is a complete circuit. Every time no matter the situation, I ALWAYS read 120 volts from neutral to hot assuming everything is wired correctly. Why is this?
Think about it, you're reference points for your meter leads are the load side of the breaker, and the neutral bar. That's why you read 120V. Doesn't matter if the load is on or not.
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Old 04-29-2018, 06:29 PM   #13
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Think about it, you're reference points for your meter leads are the load side of the breaker, and the neutral bar. That's why you read 120V. Doesn't matter if the load is on or not.
I just can't seam to picture it lol. So you have your hot and your neutral that complete the circuit, and your volts are spread throughout the circuit (hot and neutral) and it makes the amps flow equally throughout the hot and neutral, right? So why would the neutral be any different than the hot. I know the neutral goes back to the neutral and ground bar, but I still can't understand. So the neutral/ground bar makes the neutral have 0 volts, but isn't the hot and neutral connected together also within the appliance? Doesn't the hot and neutral essentially complete one big circle, amps flow through both and volts are in both as well, so why wouldn't the hot also be affected by the ground/neutral bar o_0.. Idk I just can't understand this lol

Last edited by JasonCo; 04-29-2018 at 06:34 PM.
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Old 04-29-2018, 06:55 PM   #14
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Originally Posted by JasonCo View Post
I just can't seam to picture it lol. So you have your hot and your neutral that complete the circuit, and your volts are spread throughout the circuit (hot and neutral) and it makes the amps flow equally throughout the hot and neutral, right? So why would the neutral be any different than the hot. I know the neutral goes back to the neutral and ground bar, but I still can't understand. So the neutral/ground bar makes the neutral have 0 volts, but isn't the hot and neutral connected together also within the appliance? Doesn't the hot and neutral essentially complete one big circle, amps flow through both and volts are in both as well, so why wouldn't the hot also be affected by the ground/neutral bar o_0.. Idk I just can't understand this lol
The Neutral is a grounded conductor. A voltage exists because of the difference in potential between two points. You don't have a difference in potential between the neutral and the ground, because they are bonded together. Therefore you should get no voltage, as you say, 0V.
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Old 04-29-2018, 07:04 PM   #15
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The Neutral is a grounded conductor. A voltage exists because of the difference in potential between two points. You don't have a difference in potential between the neutral and the ground, because they are bonded together. Therefore you should get no voltage, as you say, 0V.
Yes but isn't your neutral and your hot essentially the same circuit as well? Doesn't the flow of current and the presence of voltage lie within both? Doesn't your appliance that is plugged into the wall basically combine the 2 wires and make it into one? I thought that your volts are in both neutral and hot, and current flows equally through both. This is what is confusing me, why do you read 0 volts on your meter when putting your meter leads on the hot and neutral, isn't it essentially the same path with no potential difference?
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Old 04-29-2018, 07:23 PM   #16
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Quote:
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Yes but isn't your neutral and your hot essentially the same circuit as well?
Voltage drops across a load!
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Old 04-29-2018, 07:26 PM   #17
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This is what is confusing me, why do you read 0 volts on your meter when putting your meter leads on the hot and neutral, isn't it essentially the same path with no potential difference?
You can't have 0V in this scenario.

May I suggest maybe watch a couple youtube videos on basic electrical theory and circuits?

You really need to understand the basics, in order to understand how to test things using a meter, and why you get the results you see.
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Old 04-29-2018, 07:31 PM   #18
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Originally Posted by JasonCo View Post
Yes but isn't your neutral and your hot essentially the same circuit as well? Doesn't the flow of current and the presence of voltage lie within both? Doesn't your appliance that is plugged into the wall basically combine the 2 wires and make it into one? I thought that your volts are in both neutral and hot, and current flows equally through both. This is what is confusing me, why do you read 0 volts on your meter when putting your meter leads on the hot and neutral, isn't it essentially the same path with no potential difference?
What you are not grasping is difference of potential and voltage drop.

What would you measure between A phase and A phase ? 0v.(using that term loosely assuming 240/120v system) What would you measure between the phase and neutral? 120V because there is a difference of potential. What would you measure phase to ground? 120v because there is a difference of potential.

I think you are confused because you think that with the load energized there should be 0 volts. But there is resistance or impendence at that load.
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Old 04-29-2018, 08:01 PM   #19
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What you are not grasping is difference of potential and voltage drop.

What would you measure between A phase and A phase ? 0v.(using that term loosely assuming 240/120v system) What would you measure between the phase and neutral? 120V because there is a difference of potential. What would you measure phase to ground? 120v because there is a difference of potential.

I think you are confused because you think that with the load energized there should be 0 volts. But there is resistance or impendence at that load.
No I completely understand that a meter measures the difference in potential. Everything you just said I completely understand.

What splatz is saying

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Voltage drops across a load!
Okay, so if voltage drops across a load, then why do you read 120v from load side of your neutral to your ground if you take apart the splice in a junction box. If there is a junction box in the ceiling, and you undue the splice, and put your meter on the load side of the neutral and on a ground, you will read 120v. But that contradicts what you are saying that voltage drops across the load.
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Old 04-29-2018, 08:10 PM   #20
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Okay, so if voltage drops across a load, then why do you read 120v from load side of your neutral to your ground if you take apart the splice in a junction box. If there is a junction box in the ceiling, and you undue the splice, and put your meter on the load side of the neutral and on a ground, you will read 120v. But that contradicts what you are saying that voltage drops across the load.
Because the circuit is not complete, you took it apart. The load side neutral is not a neutral, it is a continuation of the hot wire through a load, and therefore you have a difference of potential between the two points you are measuring. This is why you shouldn't be undoing any junction boxes without knowing what you are doing, otherwise you'll find out that white wires can be hot, or they can have 0V on them.
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