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.

 

[CoyPatton]

Also don’t forget that the ground buss and neutral buss are separated in a sub panel.

Yes and no. Yes as grounds and neutrals leave the sub panel, there is a lack of bonding (separation/isolation). But if you travel upstream to the main panel, the 2 are bonded, typically on the bar. At this point both are typically earthed to whatever earthing system used.

 

[CoyPatton]

But labels are required to comply with code. In reality these labels (if installed) fail to remain in place for a variety of reasons.

 

[WinterDeere]

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.

Yes, very recent, when considering the age of many houses. Separation of ground and neutral was first specified in the 1999 edition of the NEC. More changes and specificity were added in 2008.

The intention on a “ground” being added to the system was to provide a backup round for the current in the event onna failure.

That is part of it. The other is ensuring the hots are only 120V relative to ground, and that you're neutral isn't ever floating more than a conductor's drop above your plumbing. People used to get shocked just touching their kitchen faucet and an appliance, at the same time.

 

[TORQUIN]

My understanding of why the ground and neutral are not bonded in sub-panels is due to the wire size of the ground conductor. The ground conductor is usually a smaller wire and cannot handle as much current as the neutral wire, therefore code does not want to have current going through the ground wire in the sub panels. The ground is only for faults.

 

[WinterDeere]

My understanding of why the ground and neutral are not bonded in sub-panels is due to the wire size of the ground conductor. The ground conductor is usually a smaller wire and cannot handle as much current as the neutral wire, therefore code does not want to have current going through the ground wire in the sub panels. The ground is only for faults.

The reason is to avoid a parallel current path, and ensure primary current never flows on the ground wire. Simple Kirchoff's theory, if you bond two conductors at both ends, they're effectively one conductor, and current will divide onto the two according to their proportional conductance.

But this has everything to do with appliance chassis safety and proper operation of things like ground-fault devices, and nothing to do with how much current the ground wire can "handle". After all, if that were the problem, they could simply specify larger ground wire conductors, equal to the size of the neutral.

Ground wires are allowed to be smaller, because they never need to carry any large current for very long. The rate of heating of a wire is inversely proportional to its cross-section (diameter^2), and the ground wire is sized to be large enough to carry the maximum breaker current for only a very brief amount of time in the event of a failure scenario, sufficient to trip the breaker.

 

[TORQUIN]

The reason is to avoid a parallel current path, and ensure primary current never flows on the ground wire. Simple Kirchoff's theory, if you bond two conductors at both ends, they're effectively one conductor, and current will divide onto the two according to their proportional conductance.

But this has everything to do with appliance chassis safety and proper operation of things like ground-fault devices, and nothing to do with how much current the ground wire can "handle". After all, if that were the problem, they could simply specify larger ground wire conductors, equal to the size of the neutral.

Ground wires are allowed to be smaller, because they never need to carry any large current for very long. The rate of heating of a wire is inversely proportional to its cross-section (diameter^2), and the ground wire is sized to be large enough to carry the maximum breaker current for only a very brief amount of time in the event of a failure scenario, sufficient to trip the breaker.

Thanks for the clarification.

 

[NibbanaFarm]

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

My friend just bought an old glass factory in Philadelphia outside of center city. PECO came to hook up the power and gave him a Scott transformer that supplied 1200V 2-phase to his building. Inside the building were huge old 2-phase step down transformers. The transformers had boiler drains to drain the dielectric oil that were right over floor drains that led to the city storm drains and into the river.

Another of his buildings in the Northern Liberties is also 2-phase.

 

[WinterDeere]

The transformers had boiler drains to drain the dielectric oil that were right over floor drains that led to the city storm drains and into the river.

Probably not uncommon, in any major city, at the time. Philly was built at the confluence of the Schuylkill and Delaware rivers, just as most confluences are populated by old cities, water being the primary forms of transportation and power at one time.

I used to water ski in the Delaware river, from Bristol down to Philadelphia, and while I don't want to even think about what might have been in that water, it probably wasn't worse than the Jersey shore water where I did the rest of my skiing. Off-shore dumping was very common along the east-coast, and the water was very noticeably dirtier in the 1970's and 1980's, but much cleaner by the early 1990's.

 

[manzer7]

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

The Earth is the ground !! If you touch the ground wire or buss and you are better grounded - you will complete the circuit and get electrocuted.
I had the experience of getting shocked on a ground wire from my tv set when I went to fix a rusting ground on my existing outside antenna and I was kneeling in a somewhat damp area and pulled the ground rod from the earth and got a tingling from the ground whereas the tv was still on.

I completed the ground for the tv. I saw a plumber that was fixing some plumbing (all copper) to the street and he got a good jolt from the ground and earth when the parts were cut to replace another part. Watch out for the ground - you do not want to be the conductor !!!

 

[WinterDeere]

The Earth is the ground !! If you touch the ground wire or buss and you are better grounded - you will complete the circuit and get electrocuted.
I had the experience of getting shocked on a ground wire from my tv set when I went to fix a rusting ground on my existing outside antenna and I was kneeling in a somewhat damp area and pulled the ground rod from the earth and got a tingling from the ground whereas the tv was still on.

I completed the ground for the tv. I saw a plumber that was fixing some plumbing (all copper) to the street and he got a good jolt from the ground and earth when the parts were cut to replace another part. Watch out for the ground - you do not want to be the conductor !!!

It's possible the voltage you were feeling was induced via the antenna sticking up in the air, and not from the receiver on the television itself. TV receivers, unless miswired or malfunctioning, should not output any high voltage. But a metal stick standing 50 feet in the air probably could pick up a charge sufficient to make you mighty uncomfortable, if left ungrounded.