Home electrical

[WinterDeere]

Because the neutral at the sub-panel may not be at ground potential.

This would be true if the load on the two phases in the sub-panel is not equal, so there is some current flowing in the neutral. With current flowing, and some small resistance in the neutral conductor, there is a voltage difference between the neutral buss in the sub-panel and the one in the main panel. Probably small, but some.

You want the ground busses in all panels to be a ground potential.

All correct, and a good explanation. But careful with confusing the word "phases" for "legs". Residential panels, with rare notable exceptions, are all single-phase. But we use two legs to make a phase, with a center tap (neutral) to split the phase.

Single phase = 2 legs = residential
Three phase = 3 legs = utility & commercial

The only reason this matters is that there are actually two-phase systems out there. Was a lot more popular 100+ years ago, in fact I think only Philly and maybe Chicago have any two-phase buildings left today, but it's out there. I believe all 2-phase systems have the two phases at 90° to one-another, whereas three phase is usually at 120° between phases.

 

[ultrarunner]

All correct, and a good explanation. But careful with confusing the word "phases" for "legs". Residential panels, with rare notable exceptions, are all single-phase. But we use two legs to make a phase, with a center tap (neutral) to split the phase.

Single phase = 2 legs = residential
Three phase = 3 legs = utility & commercial

The only reason this matters is that there are actually two-phase systems out there. Was a lot more popular 100+ years ago, in fact I think only Philly and maybe Chicago have any two-phase buildings left today, but it's out there. I believe all 2-phase systems have the two phases at 90° to one-another, whereas three phase is usually at 120° between phases.

Where does one buy 2 phase equipment?

 

[WinterDeere]

Where does one buy 2 phase equipment?

They've been phasing it out (pun?) for decades, so probably either used or custom.

I just checked, and while I was right on Philadelphia (of course), Chicago was not the second city still using it. That honor goes to Hartford CT.

"Active two-phase distribution systems remain in Center City Philadelphia, where many commercial buildings are permanently wired for two-phase,[2] and in Hartford, Connecticut.[3]"

Its prevalence is nothing more than an example of historic inertia. 2-phase was popular in the very early 1900's, and Philadelphia happened to be one of the first large cities being wired at that time. By the time other major cities came on line to the same extent, the advantages of 3-phase were already known and deployed, so they got the newer/better tech. That said, even most of Philly is 3-phase, today.

Two-phase electric power - Wikipedia

en.wikipedia.org

 

[Williy]

2 phase means 2 hot wires = 220 volts ac?

I seen the new code that all new power panels
installed in homes now have a separate bus bar
for ground sepetate from the common bus bar

willy

 

[WinterDeere]

2 phase means 2 hot wires = 220 volts ac?

That's actually single-phase. Two-phase is an odd old system most will never see in their lifetime, which typically has 4 hot wires.

Think of it like this: A phase is a transformer winding. The transformer feeding power to your home has just one secondary winding, with three wires tapped into it: L1 (hot) at one end of the winding, L2 (hot) at the other end, and a neutral in the middle of the winding. The whole mess is floating, relative to ground, until you bond neutral to ground at your mains panel.

I seen the new code that all new power panels
installed in homes now have a separate bus bar
for ground sepetate from the common bus bar

Yep. Standard. But they come with a ground-bonding tab, used to tie the neutral bus bar to ground, usually only used at the initial power entrance to the building.

 

[WinterDeere]

I guess I should have extended the theory above, to include three phase. Three phase would normally require six wires, except that one end of each transformer winding is tied to the next, so that only three wires are brought to the outside world.

This works because the phases are at 120° relationships, so that three phases tied in series brings you back around a full 360°, to the phase of the first leg.

Of course I’m talking about Delta configuration here, but that’s just a physical construct. The math works the same for Y configuration 3-phase, just with option for one extra center tap conductor.

 

[woody]

I told my Dad when I saw this thread start it was going to be pages of discussion and I was right but I have enjoyed reading every page. I have not seen where anyone has mentioned putting a neutral connection in light switch boxes, does anyone care to elaborate on the reason for this?

 

[TerryR]

I have not seen where anyone has mentioned putting a neutral connection in light switch boxes, does anyone care to elaborate on the reason for this?

I thought it was to have 120v available at the switch for automated switches, some of which require that.

 

[grsthegreat]

Its a requirement now to have a neutral at every light switch. As stated above its mainly for smart light switches, occupancy sensors, and the like. In the good old days, you did not need this.

 

[CoyPatton]

Good morning, I can’t seem to find anyone that can give me a clear answer.
The video below is as close as I have come.
The question is: if the neutral ( in most cases white ) is connected to the same bus bar as the grounds and the neutral is what carries the electricity back to the source ( which is maybe a different topic ) than why are the grounds not energized within the panel ( including but not limited to the exposed ground that I’ve placed on the exterior of my wall to ground the system)
Thank you and I hope that you all have/had someone special to spend your holiday with.
Good video here

In effect, the “ground” better term is earthed, and “neutral” are always bonded—since all sub panels are fed from the main panel where ground and neutral are in effect connected to the same bars (bonded). If your panels are old enough, the neutral and ground are bonded throughout the system. It is a relatively recent code change that specifics the 2 are “separated” in sup panels.
The intention on a “ground” being added to the system was to provide a backup round for the current in the event onna failure. There was a time, not all that long ago, that only 2 wires were used, off the top of my head I’m not certain when that changed but lots of years ago. I’m 63 the house I was raised in was one of these. It is basically my age. By the time I was old enough to help with any wiring projects, 3 wires had came about. So 45 yrs or so ago 3 wires were the thing.
Because of the separation/isolation of neutrals and grounds on in sub panels today, grounds are less of a current conductor in sub panels that when there was no separation.