n00b question about "What is a phase?"

This could go on forever but generally single phase is one sine wave, typically originating from two ungrounded conductors. The fist fight starts when you start arguing about whether you call those 2 ungrounded conductors two phases and that gets more complicated for some people when you ground the center tap of the transformer but it is still only one phase. A lot of strange language has come up around how you explain this to homeowners ("split Phase", really a type of motor winding. Two phases

180 out ... but isn't 180 degrees a straight line? The list goes on) It is single phase, get over it.

The other common implementation is 3 phase where you have 3 separate phases displaced by 120 degrees. That one usually gets by with little confusion unless you ground one corner of a delta.

There is also 2 phase but it is pretty rare and most people have never seen it. This is typically a 5 wire service and looks like a cross or plus sign with the phases being displaced by 90 degrees. A 3 wire implementation would be 3 wire looking like an ell. That is still a 90 degree displacement tho.

In the electronic world I suppose there are things with more phases but that is not anything utilities usually do.

That would be 208/120 and 480/277. In 3 phase the big number goes first. It helps you figure out what you are talking about. You are describing Wye arrangements. The line to line voltage will be line to neutral * sq/rt 3.

When you get into Delta you will see 240/120 where they ground the center tap of one of the transformers and that sq/rt 3 shows up on the

3d leg (ref ground). Line to line is 240 all the way around. This can be done with 2 transformers if the load on the 3d leg is moderate and all of the single phase load is on the grounded transformer. One transformer will usually be smaller than the other

You can also corner ground that delta and things get strange to the uneducated eye. Looking at the service, it looks just like what you have at the house, two ungrounded conductors and a white "grounded conductor" (see why "neutral" may get confusing) Usually there will only be 2 pole breakers and you could easily think you were looking at

120/240 until you measured line to ground with a meter. That is when you see you still have 240v, all the way around the triangle. The only place I have seen this is in sewer lift stations where the only load was a big pump and a control panel that runs on 240v.

Okay. So the single phase is carried by two conductors.

3? ? wiring has each phase (sine wave) carried by two corners of the ? triangle. Correct?

This seems to support my supposition that the individual conductors / wired / lines are not the phase by themselves.

I would think that if you're talking about only those two conductors without any reference to anything else, then that this is a single phase, or sine wave, carried by / between those two conductors. One as a supply and one as a return. (If I can loosely use those terms for AC.)

My limited understanding agrees. The typical home in the U.S. (I don't know about elsewhere in the world) is feed by a single phase to a transformer with a center tap that is grounded, and each of side in relation to the center tap is what I believe is called a "leg".

I've come to know that as single phase / dual leg.

Agreed.

Hum. I'm curious, but I'm likely to ignore that for a few minutes. Though it does support /not/ calling single phase / dual leg a 2? circuit.

I'm sure I'll look it up at some point.

I think you're talking about A / N / B in the following crude diagram.

A | b--N--B | a

I'm speculating that the center point would be neutral, like a 3? Y.

Agreed.

Thank you.

NFPA is trying to standardize the terms "Ungrounded Conductor", "Grounded Conductor", "Grounding Conductor" (the Grounding Electrode Conductor) and "Bonding Conductor" (the Equipment Grounding Conductors") but old habits die hard. "Grounding" vs "Bonding" seems to be the hardest sell but some at NFPA feel "Grounding" is the wire(s) that go to earth and all of the other green/bare wires are simply "Bonding" to a common point that is connected to earth. (The main Bonding Jumper)

"Ungrounded Conductor" and "Grounded Conductor" make sense enough to me.

I can't quite understand the difference between "Grounded Conductor" vs "Grounding Conductor". I guess the former is a conductor that is grounded and the latter is the specific conductor that does the grounding.

I have a problem with "Bonding Conductor". To me, that's vague, and only implies that it's the conductor that bonds to /something/. But to me, the two words "bonding" and "conductor" don't say what is being bonded to. Perhaps there is an implicit 3rd term that would make a difference; "Ground Bonding Conductor".

My biggest hangup is that "bonding" means that two things are connected together, usually quite well. As such, I think that I could "bond" two "ungrounded conductors" together.

I can see how the green / bare wired are bonded to a common point that is also bonded to a grounding conductor. But I would think that the far end of said green / bare wires form as a grounding conductor themselves. I guess do to fan out, they could be called grounded conductors as in they aren't themselves directly grounded, but rather indirectly bonded to something that is itself directly grounded.

In retrospect, I realize that this didn't actually give the answer I was looking for. Or at least I didn't understand it to be that.

As you say, the phase typically originates from two ungrounded conductors. Thus the single conductor / leg / wire is /not/ the phase.

The phase is across two ungrounded conductors; AB / BC / CA or black red / red blue / blue red. (Assuming 3 wire ?.) Or the phase is across one ungrounded conductor and a grounded conductor; AN / BN / CN or black white / red white / blue white. (Assuming 4 wire Y.) The point being that the single wire, A / B / C is /not/ the phase without another conductor to form the circuit. Correct?

I can see how if you look at the two lines from the opposite ends of the

other, thus two different phases.

However, through constructive interference with each other, they are effectively one single phase with twice the voltage when referencing each other, vs referencing neutral.

of phase with each other, I completely agree that the two legs are decidedly /not/ 2?.

I'm not sure what grounding the center tap changes. Unless it serves as

I agree that /functionally/ and /effectively/ it's 1?.

I'm aware of the corner grounded ?, but my brain doesn't want to go there tonight.

I did some light reading on 2? and agree that it's rare. Though I can see why it might be advantageous for starting motors.

I also did some light reading on split-phase motors and see how that uses a single phase, through alternate winding arrangements, to simulate two phases to start motors. Not large motors at that. Something about

1kW being the cut off point. Not high starting torque motors either.

I sort of understand that. But I think I'm going to acknowledge it and move on as I'm unlikely to ever encounter it myself.

Agreed.

On Sat, 5 Oct 2019 20:54:44 -0600, Grant Taylor wrote:

A groundED conductor is designed to carry current as part of a circuit. The groundING conductor only carries current in a fault condition. The white wire vs the green one.

Bonding is generally referring to creating an equipotential grid that is grounded. The traditional example is the bonding grid in a swimming pool or spa. Pretty much every piece of metal within 5' of the water and everything that touches the water is bonded together with 8 gauge wire. It is not really important that it is actually grounded because the swimmer is virtually a bird on a wire where everything he can touch is at the same potential. It will still be grounded though since some of the equipment required to be bonded is also required to be bonded and if this is a concrete in ground pool, you have the best Ufer ground in town. I suppose someone up in NFPA land decided this is also what we are doing with the Equipment Grounding Conductors we run all around the building and they thought it was a better term for it. The intent is still to be sure the case of that drill you are holding is at the same potential as the concrete floor you are sitting on. That is also why we do not want current on that grounding/bonding conductor (250.6). Where there is current, there is also a difference of potential at each end of the conductor carrying that current. (AKA voltage drop) Even back in the pre 1996 days when we allowed grounding the frame of dryers and ranges via the neutral, we required that this circuit originate in the panel where the grounding electrode conductor landed to minimize as much voltage shift as possible. (no feeders).

That is splicing.

Grounded conductors are in fact tied to the bus with the main bonding jumper that goes to the bus that grounds the service but it is a star wired affair and anything beyond that point is different. You will see a difference in potential on Neutral/Grounded conductors as soon as current flows but the objective is that grounding/bonding conductors are not carrying current so the voltage difference is zero throughout the system in reference to earth. Of course that is only as good as your ground electrode system. If your grounding is bad, the neutral will bring the EGC system up and you may get lit up if you are barefoot on a terrazzo floor and touch the stove. BTDT. It was the first thing I had to fix in this house, day one. It will wake you up before your coffee kicks in. Bad ground rod clamp.

It really gets down to semantics and most electricians will say "Phase A, B and C" referring to those conductors. When it is a wye, that makes perfect sense assuming neutral is a given but if it is a delta, you don't really get a phase until you connect 2 so it will be A/B, C/A etc.

Two phase is really just academic. I am not sure there are more than a few places in the world that supply it. I think maybe they still have some in Philadelphia and maybe Hartford. I assume it is done with special transformers (Scott T?) these days and not generated that way. It was just the early way of starting motors. You didn't have the capacitor technology that came later.

It really doesn't change anything. It is like standing in the middle of a stair case and deciding whether this is a stair case going up or down. It is still one staircase.

In Europe, distribution is a 3 phase 4-wire system.

Volage in the UK used to be 240V between any phase and neutral and 415V 3-phase.

Residential areas are usual connected so that a small number of homes (which could be as low as 1) is fed 240V on a single phase, the next home(s) are fed from a 2nd phase, the next from the 3rd phase and then the sequence repeats. This ensures that the loading on all phases is reasonabl balanced.

Heavy industrial users would have 415V 3-phase supplies.

Europe had 220V/380V supplies but from 2003, European voltages have been harmonized at 230V/400V although the tolerances on these voltages mean that virtually nothing has changed.

Out of curiosity, what is the typical maximum distance from the transformer to the most distant residence?

Here in the US, because of the lower voltage (for most things), they usually won't go more than 1 or 2 pole spans before the drop to the house, and many newer setups sometimes have a transformer for every house. This is for above ground installations, I can't tell about underground (most newer neighborhoods) other than how many transformer boxes there are along the street.

I have seen, however, older neighborhoods with as many as 12 houses on a single transformer, including our summer place. Originally all places had 60A service. Bad light blinking. The fact that the primary is only

4800 V delta doesn't help.

That is not exactly accurate. The single phase delivered to a residence is nominally 240v (ten higher than most of Europe.) It just has a center tap dividing that single phase into two 120v circuits. If the 120v loads were balanced there would be zero current on the neutral and you would be computing voltage drop on the 240v circuit. We actually do that with "multiwire" circuits in the home (AKA shared neutral/Edison etc).

That may sound good in theory but light blinking is usually seen when a

120V motor fed from the same hot as the light is switched on, and draws a starting surge. The drop in the hot is the main culprit, as you mentioned the neutral current is largely canceled. (I sometimes have seen a "reverse" light blink when a light on the other hot gets brighter when the motor is switched on. This is from a voltage drop in the neutral allowing the hot2-neutral voltage to rise above 120V as the current is out of phase. Rare and requires attention.)

To be quite honest, I don't know.

I grew up and, until recently, lived and worked in areas where all supplies were underground. This would be the same for towns and cities all over the UK, so the area I live in now is an exception.

If you look here:

we live in the road going off to the left just a short way down, and our feed is underground but the road didn't exist until about 60 - 70 years ago whereas the main road straight ahead has overhead feeds. There were always a few houses along this road at the time it was electrified but there were long distances between them and the area was very rural.

As you can see, these houses are pole fed but I've no idea where the sub station (transformer) is hidden - there is denitely nothing large on any of the poles.

About a year or so ago,I was having a peaceful pint or three in the local pub when my wife phoned me in a panic to say that the power had gone off. (We'd just had a lot of electrical work done and I think she suspected that was the cause!)

However, when she looked outside, the entire street was in darkness, so there was nothing either of us could do, so I went back to my pint!

When I left, I found somone on a cherry picker at the top of this pole:

As the lorry blocked the footpath, there was a man ensuring that every body got past safely and he explained that a transformer had failed and his colleague was patching everybody over to a different one.

I'd walked on about 25 yards when the streetlights came back on, which was very useful!

My wife told me that our power had come back quite quickly, so I assumed we'd been transferred to a much more accessible feed. I can't really see our street being fed from that pole - also, I don't know how much of our estate was affected.

If you follow my route back down the road you'll see the distance involved.