Heater/Motors? wiring question

[Dewskee]

Hey guys, so basically in class I've been taught that for a circuit to work it has to have a neutral, or grounded wire. So in my head whenever i'm doing anything electrical, it should have a grounded wire for it to work because it completes the path.

So I guess my question is: How come on motors and heaters...or at least on some i've worked on with my journeyman, you don't have a neutral/grounded wire? I just don't get it, it goes against what i've been taught thus far. When I asked about it, he didn't seem to really know why, just that it uses 100% of the power...which still doesn't make sense to me, b/c doesn't a circuit have to have a return path for it to be a circuit or work? If someone could explain this to me, i'd greatly appreciate it, thanks.

 

[LarryFine]

Dew, you may be confusing grounding conductors with grounded conductors. The former is the (usually) green equipment grounding conductor, and the latter is the (usually) white circuit conductor.

All electrical installations require equipment grounding, but whether a grounded circuit conductor is required depends on the load. For example, a clothes dryer requires a neutral, while a water heater does not.

Every circuit requires a complete, well, circuit for current to flow. Read this: http://forums.mikeholt.com/showpost.php?p=708650&postcount=4

 

[Dewskee]

For example, a clothes dryer requires a neutral, while a water heater does not.

Still trying to understand, let me show you the situation I was in today, that brought about my question. We were roughing in an outlet for a heater, and my journeyman was going to run 12/3 wire. Then he basically said "Nevermind, we don't need the neutral"(the white wire), so we ran 12/2 instead. He plans on just reidentifying the white wire as black. In my head, to me, this means there's no path for the current to flow back to the panel. And the part I quoted you on, means to me: A clothes dryer needs a path back to the panel to work, and a water heater doesn't.

I realize that the heater uses the voltage potential between the 2 conductors but, i still don't get how the path is completed, b/c I don't see a way for the current to get back to the panel.

 

[jim dungar]

I am trying to keep this very simple, so I am taking liberties with some terminology.

Current does not 'flow back to the panel' on any specific wire. Current flows in a loop.

On a 120V circuit the current loop includes a black wire and a white wire.
On a 240V circuit the current loop includes the black wire and the red wire.
On a 120/240V circuit there are actually three possible loops, the black and white wires, the red and white wires and the black and red wires. Which loop is actually used depends on the loads that are connected.

 

[LarryFine]

In my head, to me, this means there's no path for the current to flow back to the panel. And the part I quoted you on, means to me: A clothes dryer needs a path back to the panel to work, and a water heater doesn't.

I realize that the heater uses the voltage potential between the 2 conductors but, i still don't get how the path is completed, b/c I don't see a way for the current to get back to the panel.

There should be a bare grounding wire in either 2- or 3-conductor cables, which is the pathway back for grounding the metallic parts. A circuit only needs a grounded conductor, aka a neutral, if the device being fed requires it.

A dryer needs a grounded conductor, i.e., a neutral, because it contains components that require 120v, such as the drum and timer motors, and a light if there is one. The heating element is only wired line-to-line, and sees the full 240v.

A water heater, on the other hand, contains no 120v devices, so only requires the two lines. Both dryers and water heaters are supplied by grounding means, the bare/green wire.

The current "gets back to the panel" through all circuit conductors, whether they're grounded or hot wires. If a dryer has 1a of 120v load and 20a of 240v load, one hot will carry 20a, one hot will carry 21a, and the neutral will carry 1a.

Recoloring the white wire in a cable is perfectly acceptable because that's how cables are made, unlike a conduit method where there's no excuse for using the wrong color for the intended purpose. Theyll all have grounding means.

 

[Dewskee]

Ugh, it's still kind of confusing for me, I understand the difference between Grounding, and Grounded. And I know that current just doesn't start and end in the panel..haha. I was just trying to show you how I picture it in my head. Sorry my terminology kind of sucks, i'm just an apprentice . But anyway, Black, Red, and Blue wires, i thought, carried the current out to the load, and the white wire, carrys it back.

So far what i've gathered, in 12/2 that is ran to the heater, the black, and white(reidentified) wire both get connected to overcurrent devices in the panel, so they both carry the current out toward the load. But I guess your saying they also carry current back? If that's the case, why do we run a white wire for all the other circuits, if it can just come back on the same wire?

I'll take a quick stab- This is a 240v Circuit, and the current loop requires the black and red wire, and depending on the load, one of the two becomes the path back to the panel? If that's true, then i'm still confused though, b/c doesn't the path back to the panel have to be grounded like on every other circuit? I don't know...sorry this is so hard for me to grasp, I hope you guys aren't secretly wanting to tell me that i'm a dumbass. Thanks for your patience so far.

Unless the green wire or grounding wire is serving the purpose of the grounded wire, then i guess this would make sense, but I thought the equipment grounding wire was only there in case there's a short.

 

[don_resqcapt19]

Picture two flashlight batteries connected in series .... positive to negative. Connect a 1.5 volt lamp from the negative end of one battery to the positive end of the same battery. Connect a second 1.5 volt lamp from the negative end of the second battery to the positive end of the second battery. Connect a 3 volt lamp from the negative end of the first battery to the positive end of the second battery. The 1.5 volt lamps represent the line to neutral loads and the 3 volt lamp represents the line to line loads.

 

[jim dungar]

I'll take a quick stab- This is a 240v Circuit, and the current loop requires the black and red wire, and depending on the load, one of the two becomes the path back to the panel? If that's true, then i'm still confused though, b/c doesn't the path back to the panel have to be grounded like on every other circuit?

It appears you are falling into the mistake of assuming that current is trying to flow 'back to ground'.

Actually, current simply wants to get back to its source (i.e. the POCO transformer).

Current has no interest in flowing to dirt. The transformer has three connection points, lets call them L1, N, and L2. Many decades ago the electrical industry decided to connect N to ground, this gives a path for current on the ground to also go back to the transformer.

 

[jcole]

All you need for current to flow is a difference of potential (voltage) between two points. Connect these two points together with a load and current will flow according too ohms law.

For instance, you have two ungrounded conductors going to your water heater with a difference of potential (voltage) of 240v. Current will flow when you hook a load (element) to these two points.

Another instance. You have a appliance (range) that has 240v and 120v loads on it. So you need to have two points with a potetial of difference of 240v to connect to the 240 loads and two points with a potential of difference of 120v to connect to the 120v loads. None of these points (contductors) need to be grounded.

You dont need a grounded conductor in any system to make it work. We ground circuit conductors for saftey reasons. If you remove everything that has to with grounding and bonding on a system, it will still work. It just is not as safe.

Get a good understanding of what voltage, current, and resistance is. This is crucial to understanding ac theory IMO.

 

[Dewskee]

Alright, this is making sense to me now, i'm having to reread all the posts over and over again..but it's starting to click, at first that link Larry gave me confused the crap out of me, but now as I reread it, it's making sense. The neutral wire is there to make a 120v potential right? It doesn't matter that it's grounded at the panel, if it wasn't the circuit would still work the same way, just not safely right? I feel like i'm getting it, Thanks for the help and patience guys.

 

[charlie b]

See if this helps (I'll stay away from the math part, so that doesn't add to the confusion). The circuits we work with most often are AC (alternating current). What that actually means is that the voltage (and current) vary from going one way to going the other way 60 times per second. Let's talk about a 120 volt light fixture. It is plugged into a receptacle that has three wires attached. The black one is connected (at the other end) to the breaker. The white and green are attached to bars within the panel, and these two bars are connected to each other in that panel. We will ignore the green, in this posting. Also, lamp cord wires are not colored black and white, but for this discussion we will pretend they are.

During the "positive" half cycle, current flows from the panel, out through the breaker, via the black wire to the receptacle, via one of the lamp cord's pair of wires (the "black one") to the light bulb, via the other lamp cord's wire (the "white one") to the other side of the receptacle, via the white wire back to the panel. We'll leave it there, and consider that the circuit has been completed (no need to talk about what happens upstream of the panel for now).

During the "negative" half cycle, current flows from the panel, out through the white wire to the receptacle, via the lamp cord's "white wire" to the light bulb, via the lamp cord's "black wire" to the other side of the receptacle, via the black wire back towards the panel, and finally reenters the panel by going "backwards" through the breaker.

That is the essential nature of AC current. Half the time it is actually flowing in one direction, and the rest of the time it flows "backwards."

Now let's talk about your heater.

During the "positive" half cycle, current flows from the panel, out through one half of the two-pole breaker, via the black wire to the heater, passes through the heater and travels via the other black wire (the white one that had been remarked) back towards the panel, and reenters the panel by traveling "backwards" through the other half of the two-pole breaker.

Care to guess what happens on the "negative" half cycle?

 

[Dewskee]

During the negative half cycle it does the same thing then right? except it starts on the other wire and comes back through the other half of the two pole breaker?

Together do they basically carry back a balanced load then?

 

[LarryFine]

During the negative half cycle it does the same thing then right? except it starts on the other wire and comes back through the other half of the two pole breaker?

Yes.

Together do they basically carry back a balanced load then?

They'd do that whether on AC or DC. The same amount of current travels through both circuit wires all the time. There's never a time when current is in one circuit wire but not the other.

... except during times when there is an unintentional "leak" of current out of the loop, such as when there's a short (high current) or a shock (lower current), collectively called "faults".

 

[Don Randall]

One hundred twenty

One hundred twenty

See if this helps (I'll stay away from the math part, so that doesn't add to the confusion). The circuits we work with most often are AC (alternating current). What that actually means is that the voltage (and current) vary from going one way to going the other way 60 times per second. Let's talk about a 120 volt light fixture. It is plugged into a receptacle that has three wires attached. The black one is connected (at the other end) to the breaker. The white and green are attached to bars within the panel, and these two bars are connected to each other in that panel. We will ignore the green, in this posting. Also, lamp cord wires are not colored black and white, but for this discussion we will pretend they are.

During the "positive" half cycle, current flows from the panel, out through the breaker, via the black wire to the receptacle, via one of the lamp cord's pair of wires (the "black one") to the light bulb, via the other lamp cord's wire (the "white one") to the other side of the receptacle, via the white wire back to the panel. We'll leave it there, and consider that the circuit has been completed (no need to talk about what happens upstream of the panel for now).

During the "negative" half cycle, current flows from the panel, out through the white wire to the receptacle, via the lamp cord's "white wire" to the light bulb, via the lamp cord's "black wire" to the other side of the receptacle, via the black wire back towards the panel, and finally reenters the panel by going "backwards" through the breaker.

That is the essential nature of AC current. Half the time it is actually flowing in one direction, and the rest of the time it flows "backwards."

Now let's talk about your heater.

During the "positive" half cycle, current flows from the panel, out through one half of the two-pole breaker, via the black wire to the heater, passes through the heater and travels via the other black wire (the white one that had been remarked) back towards the panel, and reenters the panel by traveling "backwards" through the other half of the two-pole breaker.

Care to guess what happens on the "negative" half cycle?

I think Charlie actually meant to say 120 times per second--(60 cycles per second and 120 half cycles per second.) Right Charlie?

 

[LarryFine]

The AC vs. DC issue is not relevant to the OP's question. He's been under the impression that one of the circuit conductors must be grounded, meaning that the circuit must include the grounded conductor, for there to be a complete circuit.

This is not the case. It is only required that there be a circuit, a conductive pathway, between two (or more) different terminals on the source. Grounding one of the conductors is what causes the earth to be part of a possible shock hazard.

But, for the load to work, grounding a circuit conductor is non sequitur; the circuit works just the same either way. As long as there is a conductive pathway between source terminals, current will flow. The greater the resistance, the lower that current.

Note that your entire house is seen as a single, large 120/240v load, a multi-wire circuit, using two lines and the grounded neutral. 120v loads use one line and the grounded conductor, 240v loads use the two lines, and 120/240v loads use all three.

 

[SG-1]

Dewskee, if you have a power point viewer on your computer try watching this: http://www.tirebiter.net/downloads/ludecke.html
You have to keep left clicking on it to make it go as if you were giving the presentation.

This is from the first thread in the Grounding vs Bonding Forum. It shows how current flows between the transformer and a light bulb. It clearly demonstrates that a grounded conductor is not needed to make the light work. If you cannot see it from home you may be able to from school or work.