How does the typical mains power connect in the USA anyway?

[gfretwell]

Delta is still used quite a bit in small services where the customer also has a significant line to neutral load and prefers 240 L/L The power company likes it because they can do it with 2 transformers instead of 3. The down side is one of the legs ends up 208v to ground. The other 2 are just like a regular 120/240 because the system is grounded at the center tap of one of the transformers. Look at the transformers and you can tell.

3 p Wye with wye distribution 3 P delta (center tapped)

Typically they use a larger transformer on the 120/240 pair to handle the L/N loads

Here is the only example of 240 center tapped delta I have ever seen with 3 transformers (behind the Hogs Breath in Key West)

The thing that attracted my attention was it still had one larger transformer. If you trace the connections you can see it

There is also a corner grounded delta but you usually only see it in places like sewer lift stations where there is no L/N load at all. The equipment will look exactly like single phase with 2 pole breakers and a white neutral but the voltages are 240 to ground on the ungrounded legs and 240 P to P

[Harold W.]

Wild_Bill scrit:

The guy gfretwell showed us a few amps of current heading directly into the ground.

Where did those few amps come from, and where did they go?

[Harold W.]

[e-mail] scrit:

I was taught the same thing, and I'm an Industrial Engineer.

Most EEs don't learn power distribution. Most learn basic transistor theory.

But, when they cover it, at least for us, they tell us that the earth is the return.

But why does it matter if it's not? It doesn't change the wiring either way.

[trader4]

Bud-

The one and only place AFAIK that all of this is coming from is the website "How stuff works". That link at the top produces the piece apparently authored by Marshal Brain. As I understand it, he's the creator of the "How stuff works" website. ALL the references Danny has are either the exact verbage from there repeated, a link back to it, or a copy thereof. You would hope that an assistant prof would check the stuff, but who knows if she did, who actually posted it as part of the course, etc. You also have to wonder about any college that uses stuff from "How stuff works" for course material.

But there is no question it's wrong.

[trader4]

My hat's off to you Bud. Excellent job taking it apart piece by piece. What's ironic is Danny came in here not knowing the difference between a neutral and ground with a house service. Now he's hitched his wagon to an author that clearly doesn't know the difference between a neutral and a ground either.

[Harold W.]

[e-mail] scrit:

Without earth you have a big problem.

[bud--]

You are the king of pictures.

(But that should further confuse Danny. Maybe if he started with the basics...)

Corner grounded delta is also common, I have heard, for center pivot irrigation. Not likely something you have in Florida.

[trader4]

It doesn't change what wiring? If grounds had to be sized and installed to accomodate normal current flow, it certainly does change wiring in a big way. And that's just one way it changes it.

Also, we just went through the whole discussion of the difference between a neutral and a ground for a house service. Are you saying that doesn't matter either?

[Harold W.]

bud-- scrit:

The return path is intentional in so much as the system is engineered to take it all into account because it's going to happen. All over the place.

[Harold W.]

[e-mail] scrit:

You are too emotional about this. Calm down. Stop repeating yourself. Take a deep breath. This is just the net! It's not the real world.

[Harold W.]

[e-mail] scrit:

He said they all said the same thing so he probably googled the sentence. It's logical. There's nothing wrong with finding multiple references that were vetted by multiple people that say the same thing.

You seem to have a personal problem.

[trader4]

Usually there is going to be some current flow, specifically the unbalanced portion. But if the only loads on are 240V, eg oven and water heater, then you would have zero current flow in the neutral. Or if you had that and you put two 100W 120V light bulbs, one on each leg/phase, then again you'd have zero current flow in the neutral.

So, how can you NOT

Yes, if there is current flow in the neutral, then some smaller portion of that current will flow through the earth, back to the transformer. It will divide according to the impedance of the neutral vs the impedance of the earth. The neutral is going to have a lot less impedance, hence most of the current is going that way. Also, that current is incidental, it's *not* the primary path and it's not being relied on to deliver power. THAT last part is what Danny doesn't get.

Thank God.

Generally correct, except for the timing difference part. Assuming pure resistance loads, there are no timing difference in the various loads. And adding power factor, which would get you timing differences, would only obfuscate the issue.

If the loads aren't balanced, then yes a small portion of that unbalanced current is going to flow back to the transformer via earth. The vast majority of it is going to flow back via the lower impedance neutral.

You've basically got it correct. The big disagreement with Danny is that he's insisting that the power company uses the earth as a return conductor to deliver power. That's what is wrong. In the .142 amps example, it's an insignificant part of the power.

[trader4]

Who is the "she" here? Unless I'm missing something, what I think Danny showed us is the college having a copy of the same flawed explanation that Danny has posted from 6 other places. It all appears to me to have originated from the website "How stuff works", where that piece has Marshal Brain as the author.

[trader4]

You seem to not understand electricity. And Danny doesn't have multiple references that were vetted by multiple people. All I see is one original, that traces back to the website "How stuff works." That a bunch of people link to it, means not a wit. The only source that he has that might have some credibility is the assoc prof at a junior college. But again, you don't have the prof saying a damn thing, just a link back to the same old thing. Unless I missed something. We don't even know if the prof put that link up there, or it was a TA at the junior college, etc. And take a look at what Bud just posted, where he shows the author of the piece doesn't understand the difference between a neutral and ground. Apparently you don't either, because you made another post where you said it doesn't matter.

[Nightcrawler®]

[Nightcrawler®]

[trader4]

Which again shows how little you know.

Wrong.

Example: I have just a couple of 240V loads. Zero flow in neutral.

Exactly what? That current flow is tiny and incidental. It's is

*not* delivering 99.99% of the power. You could unhook the ground and power would still be delivered.

Last time after you did some experimenting your alarm system was toast. What's next?

What in the world does him showing a tiny .14 amps flowing in a ground have to do with your claim that the earth is used as the return path for power transmission?

[trader4]

Enlighten us. I hook up a 3 phase load to a 3 phase power source using 3 wires. Why must I have a problem and what exactly is that problem? Does the load get it's power and work, yes or no?

[krw]

Of course it does. It's a wye at the substation. The center *is* ground.

...and here I thought the problem was getting the wires up there in the first place.

[krw]

Nonsense.

You can't have current without a closed loop.

No current = no power.

You're blind.

The same reasons.

It certainly can be, but isn't normally.

Irrelevant.

Now talk about the other half of the story.

It's absurd to deny the fact that a "return" exists.

...and they're correct.