# Help me understand Electrical wiring

More specifically, help me understand parallel wiring in a home.

First of all, my example assumptions about a parallel wiring setup:

I’ll leave any discussion about ground wires out for now. If it’s pertinent to the discussion I assume one of you fellow dopers will let me know.

Assumption 1
A Hot wire from my breaker is wired into an electrical recep.
From there the hot wire is connected to the next recep, and the next.
3 receps wired together.

Assumption 2
on the opposite side of those three receps is a neutral wire connected to each other, and ultimately goes back through the neutral bar and is literally attached to the ground.

Assumption 3
as a device is connected to any outlet 1, 2 or 3, electricity flows through the device, out to the neutral, into the ground, completing the circuit.

Q1: is this a correct basic set up?
Q2: So help me wrap my head around this. Once electricity flow through the device and onto the neutral wire, isn’t that like making both sides a hot wire for the other devices on the circuit? And if so why doesn’t that cause problems? Is it because the device that was plugged into the circuit ‘uses up’ the electricty?

So it sounds to me like for all intents and purposes if I wired three receps together creating six outlets, that would fundamentally be the same as having one recep that had six outlets in it? Does that make sense?

I think you miss the concept of alternating current.

Alternating Current is two wires that take turns pushing electrons. when one is pushing, the other is pulling. Thats simplified but covers the basics.

The third wire that goes to the ground is the ground. It’s not part of the power supply system of your house, its part of the safety measures in any high powered electric device. If the device spikes, the extra power is ideally sent to the ground.

OK, now please tell me how this relates to my assumptions.
The neutral doesn’t go to the (literal) ground as well? Everything I’ve read indicates that the neutral wire carries the current back to the electrical panel and from there to the earth (ground).
In the case of a ground wire: The ground wire is not a part of the electrical circuit, but is desirable for prevention of electric shock.

Has nothing to do with AC versus DC.

When you plug in and turn on something, electricity flows through it, but there is still 120 Volts across it. It’s the voltage that matters for Hot versus Neutral. The wires in your walls have a very small resistance, so the voltage is essentially the same across all the different devices, whether you have one, two, or more plugged in (until you pull too many amps, and trip the breaker.

For one device drawing one amp, there’s one amp flowing though the hot wire, into the device, and back through the neutral*. For two devices, each pulling one amp, there are two amps flowing through the hot, one amp through each device, and two back through the neutral. But always 120 Volts across the device(s).

(*) Yeah, yeah, it’s really AC.

What color are the wires?

Why?
In the USA Hot is traditionally black, neutral is traditionally white, and ground is traditionally stripped or green.

Even if the neutral wire is connected to ground somewhere, it doesn’t have to be. A lot of folks (engineers especially) seem to have the impression that every circuit must have a ground in it somewhere, but that’s just not true. You certainly can have some spot in the circuit that’s at the same potential as the earth, and if you do, it won’t hurt things to connect that spot to the ground, but it doesn’t make much difference. Current will never flow through the ground unless something’s gone wrong.

Just needed to make sure we were talking an AC system here.

I’d hate to give you AC advice if you had an industrial three phase system.

Leave out “ground” for the moment.

Electricity flows in a “circle”, or a circuit. The electricity goes out from the generator on one wire, and has to come back on another wire. Disconnect either wire, and you’ve got no electricity.

AC means “Alternating Current”, which means it makes a sine wave. It flows in one direction, slows down, then switches and flows in the other direction, slows down, then goes back in the first direction, etc. over and over again. It goes through a complete cycle (switching one direction then the other) 60 times per second in the U.S. In other areas, it switches 50 times per second, but it’s the same basic concept.

So, from a current flow standpoint, there really isn’t a difference between the “hot” and the “neutral” wire. In each wire, the current flows in one direction, and then the other. But whichever way the current is flowing, it needs to go out and back from the generator, so if you disconnect either wire, the current stops.

Now let’s get back to the concept of “ground”.

You can run an ungrounded system. In fact, hospitals do it all the time. It’s called an "isolated’ power system. The next time you are in a hospital, look for the red outlets. Those are isolated. Isolated systems are nice because you can touch either wire alone and not get shocked. You have to touch both wires to form a circuit, and then you get shocked.

Homes aren’t isolated. They are grounded. All they do is arbitrarily pick one of the wires, and call it “ground”. This wire is connected to the earth. Literally. I mean, they drive a copper rod into the dirt and attach a wire to it (in older homes it may just use the water pipe, but it’s the same thing). Now you don’t have an isolated system. To differentiate the wires, the one that is connected to the ground is called the “neutral” wire, and the one that isn’t is the “hot” wire, and they are given different colors. The reason for the names is obvious if you touch the wires while touching something that is electrically connected to the earth. If you touch the neutral wire, nothing much happens. But, if you touch the hot wire while you are touching earth, you complete the circuit and you get shocked.

So, you’re thinking, that’s stupid. Why not run the whole thing ungrounded, if it’s safer? Well, the reason is that it is awfully difficult to keep an isolated system isolated. Hospitals go through all kinds of efforts and even have yearly testing done on every single outlet to make sure they stay isolated. If you try to run a large electrical system (like to a bunch of houses) all isolated, you find that Mother Nature likes to randomly insert grounds everywhere. A tree branch can touch a line and short it to ground, for example. The power company simply doesn’t have the manpower to keep a large system like the U.S. electrical system ungrounded. Plus, you’ve got issues with lightning strikes and stuff like that. Having the system grounded makes it more immune to lightning, solar flares, and that sort of thing.

It used to be that homes only had two wires, hot and neutral. But this can cause you problems. If you’ve got some sort of electrical device or appliance and it has a metal case, you want to connect that case to the neutral since it is safe to touch. If you don’t, the hot wire could short to the case and you’d have this great big “hot” connection that could easily shock you. But what happens if there’s a fault on your neutral line? In that case the entire case could end up “hot” and again you’d have something dangerous. So, to protect against that, they added a third wire into the system, called the “ground”. This is a protective ground, and it never has current flowing through it. It’s a straight shot from the case of your device to earth ground. This way, in all of the different scenarios of a wire short circuiting to the case of your electrical device, you are much less likely to get shocked.

The earth does conduct electricity, so it is technically possible to take one wire from your generator and shove it into the ground, and take the neutral from your house and just shove it into the ground too. This saves you half of the cost of your wiring, since now you only need the “hot” wire. Power companies actually used to do this sometimes back in the early days, but it caused problems. Your “earth” connection isn’t always the greatest electrical connection, and varied with how wet the ground was and all sorts of other factors. So, these days, while everything is grounded (for residential circuits at least), the “earth” isn’t carrying the current back to the generator. The electricity isn’t going into the ground. It’s going back to the generator through the wires.

Physically, you have a transformer on the distribution line. One of these lines is connected to the earth, literally, through a grounding rod. All of the neutrals (the white wires) in your house are also connected to this grounding rod. All of the grounds (the green wires) are also connected to the grounding rod, at one point and one point only, and this point must be physically close to the grounding rod.

In older homes, the cold water pipe served as the grounding rod. This isn’t done any more.

Anything big and metal in your house is usually grounded. Even though we don’t use the water pipe as an earth ground, all of the water pipes in your home are grounded. You wouldn’t want them to “float” (not be connected to anything) since then a hot wire could short to them and you wouldn’t know it until you touched it and got shocked.

Since you posted this nonsense: “If the device spikes, the extra power is ideally sent to the ground,” I don’t think you should be giving advice on electrical wiring.

One more thing I think you need help with here.

Generators and batteries are “voltage sources”, which means that they try to keep the voltage constant no matter what you connect to them. So, no matter what you connect between the hot and neutral, the generator is going to try to keep the hot line at 120 volts AC, and the neutral line at 0 volts (earth ground).

The reason your device doesn’t turn the neutral line into a hot line is because your device “resists” or “impedes” the flow of electricity. The electricity can’t just flow from the hot onto the neutral. Your device is only letting a certain amount of current flow. If you were to connect something with no impedance between the hot and neutral lines, then yes, they would effectively become the same line.

In the real world, you’d also blow something up, because a voltage source applied to a zero impedance yields an infinite amount of current. Since real world generators and wires and such can’t handle that much current, something breaks (hopefully just a circuit breaker pops).

As long as your device has a reasonable amount of impedance, the generator will keep the lines at their correct voltage, because that’s what a generator does. Any device that comes along sees the same voltage between the two wires, so as each device gets connected, it doesn’t affect other devices on the line. The generator however does have to supply more current to handle all of the devices and keep the voltage up where it belongs.

Generators try to keep the voltage constant, but they do have their limits. What happens if you put too many devices on the system and the generator can’t keep up? Then the voltage drops. You may have heard the term “brownout” before. That’s what this is. The voltage drops. your lights go dim, and lots of stuff in your house doesn’t work right. If you overload the generators too much, then the circuit protection shuts them off, and you get a complete power failure (blackout).

Your home is designed in such a way that you can’t cause yourself a brownout. The breakers will trip before you cause enough of a problem to reduce the voltage. The power company can get overloaded, and may intentionally induce a brownout just so that they don’t end up in a blackout situation. Some power is better than none, in most cases.

Um, that’s a little misleading. To be perfectly clear, the circuit between the house and the transformer has two hot wires, at a voltage difference of 240V. Most household appliances run on 120V, so they plug into sockets wired with one hot wire and one neutral wire that runs to ground, as well as a ground wire that also runs to ground. The appliance’s plug connects the ground wire to the case, as said above, and the neutral wire and the hot wire connect to the appliance’s load (filament, motor, resistance coil, whatever). Very demanding appliances, such as electric stoves and electric dryers, run on 240V; these plug into special sockets wired to both hot wires, and have special plugs so you can’t get them mixed up.

As to your question, in case you haven’t gotten it from the above answers: no matter how many circuits you complete, or much power you run through your mains, the voltage is always the same (that’s regulated by the generator), but the current (amperage) increases, up to the limit of your breaker or fuse.

ETA: started this post before engineer_comp_geek added that 2nd post – good stuff, there.

Why? Do you think industrial 3-phase systems are DC? They are AC, just a different arrangement of transformer wirings & voltage levels. There’s hardly any public DC systems left at all in this country.

Good stuff from engineer_comp_geek, as usual. While I agree that you can’t cause a major brown-out, try getting something stuck in your vacuum cleaner and you’ll experience a minor brown-out. The impedance on an AC motor goes way down when the motor isn’t turning (due to the lack of a back-emf, it effectively becomes a very low resistance wire connecting the hot and neutral wires), and you get a drop in voltage in your house. You can also ruin your vacuum cleaner.

I don’t see how the fact that it’s AC is relevant. There would be an asymmetry between the wires in that electrons flowed in opposite directions in the two wires, but what does that change? People analyzed circuits before they knew of the existence of electrons (as I understand it, that’s how we wound up with the counter-intuitive convention that has current, in the sense of the mobile carriers, moving from negative to positive).

A system with out a bonded neutral is a floating system. The voltage to ground on both the hot and neutral leg can float between 120 to 0 volts on a 120 volt system. that means it is not saafe to touch either wire.

The neutral is “bonded” to the grounded at the transformer to keep the neutral at 0 volts above ground.

On a three phase delta wound system there is voltage from any leg to ground. ON a 208 volt system it will be 120, on a 480 system it will be 277.

I’m not doubting but can you explain how this works? If you touch any one wire on an isolated system and a (large enough?) conductive surface at a different potential you’ll get shocked no? So it seems worse than a grounded system to me.

No, because they use a transformer to isolate the circuit. There is no conduction path from the secondary side of the transformer to ground, so being grounded and touching either side of the isolated circuit is safe. If you don’t believe me, try measuring the voltage from ground to the output of a “wall-wart” transformer with a meter - it will be zero volts.

BTW, this is known as Galvanic Isolation.

Got it, thanks. I actually knew about galvanic isolation, I believe it’s used to isolate conventional household phones from the network, I just didn’t make the connection (heh).

Cecils book "The Barn House’ actually has quite a bit of useful info as regard this.