220V dryer sparked on startup (3 wire) What to test?

[trader4]

Then instead of just saying "wrong", why don't you explain the difference?

Test question:

A graph of three sine waves is given, A, B and C, B is shifted 90 deg from A. C is shifted 180 deg from A and looks like it's opposite.

Question:

1 - What is the phase realtionshiof B to A? 2 - What is the phase realtionship of C to A?

My answer to 1 is B is 90 deg out of phase relative to A.

My answer to 2 is C is 180 deg out of phase relative to A. To a lay person, it could also be called it's "opposite".

How those waveforms are derived, what else you call them in a particular application, doesn't change the fact of what they are and their relationship to each other. There are many ways that such voltage waveforms could be generated. It doesn't change the fact that in a 240V residential service the two hots are in fact

180 deg out of phase realtive to each other.

[Wes Groleau]

The reference is neutral. Each "hot" is 180º from the other when the correct reference is used.

[Wes Groleau]

Could be--IFF there were an available path to earth through you.

Otherwise, you might have absolutely no clue that you just did something stupid.

[krw]

No, it's not. Words mean things. Phase has a particular meaning and a phase shift and inversion are different things. In degenerate cases they may look the same but they're not. Call things by their proper names and communication gets easier. Or not, spread lies. Your choice.

[krw]

You claim to be an engineer. You should know better.

For the simple degenerate case of a pure sign wave, they'll look the same. That is *NOT* the general case and that is not how the words are defined.

Words mean things. You can use them to lie all you want but I'll call you on it.

[Nightcrawler®]

The proper term is grounded conductor, and it is white. The grounding conductor is green.

White carries device current/current imbalance. The green/bare wire equalizes potential and provides a dedicated fault path for the circuit breaker in case there is a short to any bonded (to ground) metal surface/raceway where the conductors are present.

There is no such thing as a neutral in a single phase application.

[Nightcrawler®]

Nothing wrong with that as long as the installation is installed per code. You may ground every metal thing in your house, if you want to.

[Nightcrawler®]

Not always. Older, or cheap, load centers used to do this, but the newer panels give a dedicated ground bus with a tapping screw to the panel case and an isolated grounded conductor bus.

In some instances, in meter-main/load center combos, the tapping screw may be allowed as the point at which the grounded conductor obtains its bond to ground, but it is preferred to do this in the meter section of all installations so that there is no messing things up via some moron coming in at a later time and thinking that it is all the same...

Why I hated residential work...

[Nightcrawler®]

No, it is single phase, or split phase. Only one phase is used and is center tapped to split the voltage. It is impossible for this circuit to be out of phase with itself.

Bi, or to be more precise, two-phase, is a rare entity that is primarily used in military applications, specifically in aviation. My old Air Force generator had the ability to provide two-phase, and pretty much anything else that you wanted from selection of voltage to three-phase delta or wye.

[Danny D'Amico]

Interestingly, mine has a white wire going to a green bolt.

:)

[Danny D'Amico]

I had posted a detailed answer but it got lost since aioe is eating up my posts, so, I'll reply again that I think they're 120 degrees out of phase.

Here's why I think that.

The 3 wires on the street distribution line are all hot wires. They come from a transformer (a whole series of them) which is wired with three coils. Hence, they're each 120 degrees out of phase with each other (Y or delta coils).

Then you take *two* of those hot wires, and send them into your house. Those two are *still* 120 degrees out of phase (AFAIK).

You stick a neutral wire in between (which is just a wire to ground at the poles) and now you have either two 120 volt circuits, or one three-wire

240 volt circuit.

The key point is that they're 120 degrees out of phase. I don't remember the math, but that knocks the RMS (or whatever it's called) voltage to something like 208 volts (but I don't remember the exact equation).

Anyway, since they're *not* 180 degrees out of phase, there will be current in the neutral. Actually, I guess if the two hot wires are not used for anything else, i.e., if they're a *dedicated* circuit, I'm not sure if any current still goes into the neutral.

Does anyone know if dryers are dedicated circuits? If so, is there any current going into the neutral?

Note: If they were *not* dedicated circuits, then for sure there could easily be current in the neutral since the loads wouldn't be balanced all the time.

[Danny D'Amico]

I'm pretty sure I learned, long ago, that they're 120 degrees out of phase with each other.

The reason, IIRC, has to do with the fact that they generate electricity with three coils. And *those* three coils are wound symmetrically (i.e., in a Y or delta) which makes them 120 degrees out of sync.

So, each of the three wires coming out of the power company (which are the three wires on the poles along the street) are

120 degrees out of sync (if I'm correct).

You only get *two* of those wires going into your house. But they're still 120 degrees out of sync (AFAIK).

Besides, if they were 180 degrees out of sync, what would the third wire be on that pole?

[Danny D'Amico]

Yup. The neutral carries current, a ground isn't supposed to carry current (unless something goes wrong).

That's why it threw me when I realized this neutral is connected to the case of the dryer.

So, I do see that the ground and the neutral are muddled here, in that the neutral is also the ground for the dryer frame.

So, I guess, a neutral can also function as a ground; but I wouldn't want to see a ground functioning also as a neutral.

NOTE: I sure *hope* the ground wires and neutral wires are attached to *different* points (both at zero potential) at the circuit panel.

I had always thought the ground goes into the ground at the house; but that the neutral goes into the ground at the pole (and not necessarily the first pole from the house but not more than 2 or

3 poles after the house).

Is any of that correct? Or am I wrong (again)?

[Danny D'Amico]

Well, that answers my question as to whether the neutral is carrying current.

Since there are 120v "things" on that dryer (e.g., the timer, the bulbs, etc.), there *must* be some current in that neutral (unless the loads are perfectly balanced).

So, in the case of my 3-wire dryer, the neutral is always carrying current, whereas a ground wire shouldn't normally be carrying current (because once you carry current, there is a chance that there will be resistance, and if there is resistance, you get a potential, whether you like it or not).

So, maybe, just maybe, my spark, is due to a high-resistance neutral? Geez. How do I check for a high-resistance neutral?

[Nightcrawler®]

It is wrong of them to do this, but I guess some moron engineer thought this would not confuse someone, though in this application I do not see how. In a hard wired installation, yes. Still wrong. Bonding jumpers are to be green/bare/yellow with green stripe if you are into non-American color coding.

That wire still needs to be terminated, or have a separate wire, terminated to the center terminal. This will be your chassis ground or what is called a bonding jumper.

[Nightcrawler®]

Time for football. TTYL

[Nightcrawler®]

As an aside, I would trace that wire and find out where it goes. Odds are that it is supposed to be terminated to the center terminal.

[Danny D'Amico]

I do not know the answer to that question, but, I do know that all the hot wires on the distribution power poles are supposedly bare.

[Mark Lloyd]

I'm looking at the receptacle chart at

The normal three-wire dryer receptacle appears to be on line 10 (125/250V). This receptacle has 2 hots and neutral. This is different from line 6 (250V with ground).

[sam E]

If the angle between the phases was anything other than 180, would you call it 2 phase? If so, why this oddity?