Why is the neutral tied to ground in USA single phase wiring

I was thinking about this last night as I fell asleep. I was thinking
that if neither of the wires in a single phase system were connected
to ground then it would be like using an isolation xmfr. Touching
either line and ground wouldn't shock me. But that's not the way we do
it so there must be a good reason why not.
Thanks,
Eric

 

[whit3rd]

On Monday, July 18, 2016 at 3:11:10 PM UTC-7, et...@whidbey.com wrote:

... if neither of the wires in a single phase system were connected
to ground then it would be like using an isolation xmfr. Touching
either line and ground wouldn't shock me. But that's not the way we do
it so there must be a good reason why not.

In some industrial wiring, the phases all float (and when a fault occurs, the
plant can keep running). But, when scheduled maintenance day comes around,
there MUST be a resolution of that fault: otherwise, a second insulation
failure will blow up the transformers...

Home wiring has breakers, and a fault is expected to pop a circuit breaker, giving
warning that something must be repaired. Almost all insulation faiures are connections
to grounded cases, or structure or plumbing metal, and by code all those
must be bonded to the building's grounding system.

 

[Tom Biasi]

On 7/18/2016 6:11 PM, etpm@whidbey.com wrote:

I was thinking about this last night as I fell asleep. I was thinking
that if neither of the wires in a single phase system were connected
to ground then it would be like using an isolation xmfr. Touching
either line and ground wouldn't shock me. But that's not the way we do
it so there must be a good reason why not.
Thanks,
Eric

Current will flow through you to ground whether the power company
references ground or not. In the past, I don't know if it's still true,
farms would receive just the hot wire. It was up to the user to supply
ground.

 

[DJ Delorie]

etpm@whidbey.com writes:

I was thinking about this last night as I fell asleep. I was thinking
that if neither of the wires in a single phase system were connected
to ground then it would be like using an isolation xmfr. Touching
either line and ground wouldn't shock me. But that's not the way we do
it so there must be a good reason why not.

Because some parts of the electrical grid are at higher voltages (I've
got 7200 volts or so coming up my driveway) and if something happened
(storm, trees, transformer failure, etc) that shorted part of *that*
wire, you might find that your 120 volt outlet was a couple thousand
volts hotter than you'd expect.

And probably other reasons.

 

On Mon, 18 Jul 2016 19:32:07 -0400, Tom Biasi <tombiasi@optonline.net>
wrote:

On 7/18/2016 6:11 PM, etpm@whidbey.com wrote:
I was thinking about this last night as I fell asleep. I was thinking
that if neither of the wires in a single phase system were connected
to ground then it would be like using an isolation xmfr. Touching
either line and ground wouldn't shock me. But that's not the way we do
it so there must be a good reason why not.
Thanks,
Eric

Current will flow through you to ground whether the power company
references ground or not. In the past, I don't know if it's still true,
farms would receive just the hot wire. It was up to the user to supply
ground.

If current will flow to ground then why does an isolation xmfr protect
me? Wouldn't the power company need to have one wire going to ground
for me to get shocked?

 

[Tom Biasi]

On 7/18/2016 8:41 PM, etpm@whidbey.com wrote:

On Mon, 18 Jul 2016 19:32:07 -0400, Tom Biasi <tombiasi@optonline.net
wrote:

On 7/18/2016 6:11 PM, etpm@whidbey.com wrote:
I was thinking about this last night as I fell asleep. I was thinking
that if neither of the wires in a single phase system were connected
to ground then it would be like using an isolation xmfr. Touching
either line and ground wouldn't shock me. But that's not the way we do
it so there must be a good reason why not.
Thanks,
Eric

Current will flow through you to ground whether the power company
references ground or not. In the past, I don't know if it's still true,
farms would receive just the hot wire. It was up to the user to supply
ground.
If current will flow to ground then why does an isolation xmfr protect
me? Wouldn't the power company need to have one wire going to ground
for me to get shocked?

The iso will prevent hot chassis. If the voltage is sufficient current
will find ground.

 

[Nobody]

On Mon, 18 Jul 2016 15:11:55 -0700, etpm wrote:

I was thinking about this last night as I fell asleep. I was thinking that
if neither of the wires in a single phase system were connected to
ground then it would be like using an isolation xmfr. Touching either line
and ground wouldn't shock me. But that's not the way we do it so there
must be a good reason why not.

With that much wire, something's bound to get connected to ground sooner
or later. At which point, the other side would become live. And you
wouldn't find out about this until you touched it.

Consider the following sequence of events:

1. Intial state: nothing is grounded.

2. Worn insulation results in one wire (let's call it A) shorting to the
metal case on your toaster. But as nothing is grounded, touching the case
is just going to temporarily reference A to ground. But on its own,
there's no noticeable effect.

3. Your neighbour bangs a nail through wire B and into a metal water pipe.
Now B is permanently referenced to ground and A is at 120V relative to
ground. But still no (immediate) noticeable effect.

4. The next time you touch the case on your toaster, you complete the
circuit.

Connecting ground to neutral means that a short between live and ground is
a short between live and neutral, which will trip a breaker or blow a
fuse. A short between neutral and ground will trip a RCD (GFCI) if there
is one (but as neutral is already connected to ground not far away, it
doesn't make that much difference anyhow).

 

[Tim Wescott]

On Mon, 18 Jul 2016 15:11:55 -0700, etpm wrote:

I was thinking about this last night as I fell asleep. I was thinking
that if neither of the wires in a single phase system were connected to
ground then it would be like using an isolation xmfr. Touching either
line and ground wouldn't shock me. But that's not the way we do it so
there must be a good reason why not.
Thanks,
Eric

Oi. It's complerkated.

This is all from memory -- a search on "history of North American wiring"
might find some interesting info.

A long time ago, in a galaxy far, far away, 110V was actually 110V, and
the transformer was isolated at the pole, so both legs were floating.
Appliances were on 2-wire cords with metal cases and not much isolation,
because if there was any one fault -- well, the lines were isolated.

(And the wire was cloth-wrapped or bare, and set on insulators about
three to six inches apart -- oh, those musta been the days!)

This ended up causing all sorts of problems when you _did_ get more than
one fault, and sometime in the 60's or the 70's they changed over to the
current system (perhaps with non-polarized plugs but with ground pins).

The way it's supposed to be done is that neutral is connected to ground
at one point, in a way that ground remains at true ground potential, and
neutral can float a bit off of that point (it can be several volts off of
ground, depending on your setup and what you have turned on).

The ground wire is a safety ground, so that if either power or neutral
shorts to ground, you don't greet your ancestors earlier than scheduled.
In places where it's considered _really_ important, you're required to
use GFI circuit protectors, which sense ground faults (basically, shorts
to neutral), and turn the whole thing off.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I'm looking for work -- see my website!

 

>"Edison was right: we should have a DC distribution system. But >mosfet based dc/dc converters and VFD's weren't yet invented in >Edison's time. "

It would be quite feasible today. In fact somewhere I know they did use DC, there was this story about s guy using a potato to find out the radio was plugged in backwards and that was why it did not work.

I wonder how the hell to Google that...

 

On Mon, 18 Jul 2016 22:43:44 -0500, Tim Wescott
<seemywebsite@myfooter.really> wrote:

On Mon, 18 Jul 2016 15:11:55 -0700, etpm wrote:

I was thinking about this last night as I fell asleep. I was thinking
that if neither of the wires in a single phase system were connected to
ground then it would be like using an isolation xmfr. Touching either
line and ground wouldn't shock me. But that's not the way we do it so
there must be a good reason why not.
Thanks,
Eric

Oi. It's complerkated.

This is all from memory -- a search on "history of North American wiring"
might find some interesting info.

A long time ago, in a galaxy far, far away, 110V was actually 110V, and
the transformer was isolated at the pole, so both legs were floating.
Appliances were on 2-wire cords with metal cases and not much isolation,
because if there was any one fault -- well, the lines were isolated.

(And the wire was cloth-wrapped or bare, and set on insulators about
three to six inches apart -- oh, those musta been the days!)

This ended up causing all sorts of problems when you _did_ get more than
one fault, and sometime in the 60's or the 70's they changed over to the
current system (perhaps with non-polarized plugs but with ground pins).

The way it's supposed to be done is that neutral is connected to ground
at one point, in a way that ground remains at true ground potential, and
neutral can float a bit off of that point (it can be several volts off of
ground, depending on your setup and what you have turned on).

The ground wire is a safety ground, so that if either power or neutral
shorts to ground, you don't greet your ancestors earlier than scheduled.
In places where it's considered _really_ important, you're required to
use GFI circuit protectors, which sense ground faults (basically, shorts
to neutral), and turn the whole thing off.

Thanks Tim and Nobody. Those two answers really make sense and show
how the system evolved.
Eric

 

[John Larkin]

On Mon, 18 Jul 2016 17:41:21 -0700, etpm@whidbey.com wrote:

On Mon, 18 Jul 2016 19:32:07 -0400, Tom Biasi <tombiasi@optonline.net
wrote:

On 7/18/2016 6:11 PM, etpm@whidbey.com wrote:
I was thinking about this last night as I fell asleep. I was thinking
that if neither of the wires in a single phase system were connected
to ground then it would be like using an isolation xmfr. Touching
either line and ground wouldn't shock me. But that's not the way we do
it so there must be a good reason why not.
Thanks,
Eric

Current will flow through you to ground whether the power company
references ground or not. In the past, I don't know if it's still true,
farms would receive just the hot wire. It was up to the user to supply
ground.
If current will flow to ground then why does an isolation xmfr protect
me? Wouldn't the power company need to have one wire going to ground
for me to get shocked?

The power lines could be balanced, 60-0-60 volts line-ground-line. 60
volts is much less dangerous than 120.

The power lines usually run to a lot of houses, so it would be hard to
keep the entire subnet truly isolated. The 60-0-60 thing could be
done.

The US 240 volt standard is usually 120-0-120, which is safer than the
european 240-0 thing.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[John Larkin]

On Tue, 19 Jul 2016 08:32:10 -0700, etpm@whidbey.com wrote:

On Mon, 18 Jul 2016 22:43:44 -0500, Tim Wescott
seemywebsite@myfooter.really> wrote:

On Mon, 18 Jul 2016 15:11:55 -0700, etpm wrote:

I was thinking about this last night as I fell asleep. I was thinking
that if neither of the wires in a single phase system were connected to
ground then it would be like using an isolation xmfr. Touching either
line and ground wouldn't shock me. But that's not the way we do it so
there must be a good reason why not.
Thanks,
Eric

Oi. It's complerkated.

This is all from memory -- a search on "history of North American wiring"
might find some interesting info.

A long time ago, in a galaxy far, far away, 110V was actually 110V, and
the transformer was isolated at the pole, so both legs were floating.
Appliances were on 2-wire cords with metal cases and not much isolation,
because if there was any one fault -- well, the lines were isolated.

(And the wire was cloth-wrapped or bare, and set on insulators about
three to six inches apart -- oh, those musta been the days!)

This ended up causing all sorts of problems when you _did_ get more than
one fault, and sometime in the 60's or the 70's they changed over to the
current system (perhaps with non-polarized plugs but with ground pins).

The way it's supposed to be done is that neutral is connected to ground
at one point, in a way that ground remains at true ground potential, and
neutral can float a bit off of that point (it can be several volts off of
ground, depending on your setup and what you have turned on).

The ground wire is a safety ground, so that if either power or neutral
shorts to ground, you don't greet your ancestors earlier than scheduled.
In places where it's considered _really_ important, you're required to
use GFI circuit protectors, which sense ground faults (basically, shorts
to neutral), and turn the whole thing off.
Thanks Tim and Nobody. Those two answers really make sense and show
how the system evolved.
Eric

Edison was right: we should have a DC distribution system. But mosfet
based dc/dc converters and VFD's weren't yet invented in Edison's
time.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[DaveC]

On 19 Jul 2016, John Larkin wrote
(in article<f0ksob9csrpooba49j2lfvemp5d5av8u74@4ax.com&gt:

> Edison was right: we should have a DC distribution system.

Why? Inquiring minds...

 

[Teodor V.]

On 2016-07-19 18:04, John Larkin wrote:

On Mon, 18 Jul 2016 17:41:21 -0700, etpm@whidbey.com wrote:

On Mon, 18 Jul 2016 19:32:07 -0400, Tom Biasi <tombiasi@optonline.net
wrote:

On 7/18/2016 6:11 PM, etpm@whidbey.com wrote:
I was thinking about this last night as I fell asleep. I was thinking
that if neither of the wires in a single phase system were connected
to ground then it would be like using an isolation xmfr. Touching
either line and ground wouldn't shock me. But that's not the way we do
it so there must be a good reason why not.
Thanks,
Eric

Current will flow through you to ground whether the power company
references ground or not. In the past, I don't know if it's still true,
farms would receive just the hot wire. It was up to the user to supply
ground.
If current will flow to ground then why does an isolation xmfr protect
me? Wouldn't the power company need to have one wire going to ground
for me to get shocked?

The power lines could be balanced, 60-0-60 volts line-ground-line. 60
volts is much less dangerous than 120.

The power lines usually run to a lot of houses, so it would be hard to
keep the entire subnet truly isolated. The 60-0-60 thing could be
done.

The US 240 volt standard is usually 120-0-120, which is safer than the
european 240-0 thing.

235/400 V 3-phase you mean XD ? That's the common arrangement nowadays,
3-phase to each home, but there are places where you haven't, where you
have 135/235V delta 3-phase (potentially floating). For the 235/400
systems, N is usually tied to PE, like on your side of the pond.

There are pro's and con's with either voltage system and system
frequency. Like, reactive losses are ever so slightly worse at 60 Hz,
and from that standpoint a DC system would be super, but switching
complicates it.

Resistive losses in wiring are higher at 120V, like for a vanilla
household circuit you can't get much higher than 1,800W your side of the
pond (assuming 15A breaker), while here, we gets 500W more juice and
thinner wiring (assuming 10A breaker).

But I'm not much for voltage/frequency wars, a lot of it has to do with
how the grid developed etc and changing the systems would be an
undertaking unprecedented in cost and work. If there's anything I'd have
the gall to suggest to you 'merkins it's to consider 3-phase to
households (120/210-ish) as opposed to split-phase as you have now, I
think it would give benefits in terms of power consumption as well as
load being even over the phases. And all for just one extra wire.

As to safety, I would say anything above 60-70V or so is inherently
dangerous, but the lower you are in voltage the more forgiving it tends
to be in terms of small mistakes. I mean, dead shorts at 235 are LOUD,
and 400 dead shorts are more or less as loud as gunshots. If anything,
living in 235 territory has taught me to respect the authoritae of mains
and to design and wire accordingly.

Oh, and don't get me started on my pet peeve of the connectors on this
side of the pond...

/Teo.

--
Teodor Väänänen | Don't meddle in the affairs of wizards,
teostupiditydor@algonet.se | for you are good and crunchy with
Remove stupidity to reply | ketchup.

 

On Tue, 19 Jul 2016 09:08:28 -0700, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

On Tue, 19 Jul 2016 08:32:10 -0700, etpm@whidbey.com wrote:


On Mon, 18 Jul 2016 22:43:44 -0500, Tim Wescott
seemywebsite@myfooter.really> wrote:

On Mon, 18 Jul 2016 15:11:55 -0700, etpm wrote:

I was thinking about this last night as I fell asleep. I was thinking
that if neither of the wires in a single phase system were connected to
ground then it would be like using an isolation xmfr. Touching either
line and ground wouldn't shock me. But that's not the way we do it so
there must be a good reason why not.
Thanks,
Eric

Oi. It's complerkated.

This is all from memory -- a search on "history of North American wiring"
might find some interesting info.

A long time ago, in a galaxy far, far away, 110V was actually 110V, and
the transformer was isolated at the pole, so both legs were floating.
Appliances were on 2-wire cords with metal cases and not much isolation,
because if there was any one fault -- well, the lines were isolated.

(And the wire was cloth-wrapped or bare, and set on insulators about
three to six inches apart -- oh, those musta been the days!)

This ended up causing all sorts of problems when you _did_ get more than
one fault, and sometime in the 60's or the 70's they changed over to the
current system (perhaps with non-polarized plugs but with ground pins).

The way it's supposed to be done is that neutral is connected to ground
at one point, in a way that ground remains at true ground potential, and
neutral can float a bit off of that point (it can be several volts off of
ground, depending on your setup and what you have turned on).

The ground wire is a safety ground, so that if either power or neutral
shorts to ground, you don't greet your ancestors earlier than scheduled.
In places where it's considered _really_ important, you're required to
use GFI circuit protectors, which sense ground faults (basically, shorts
to neutral), and turn the whole thing off.
Thanks Tim and Nobody. Those two answers really make sense and show
how the system evolved.
Eric

Edison was right: we should have a DC distribution system. But mosfet
based dc/dc converters and VFD's weren't yet invented in Edison's
time.

Yeah, I can see several advantages to having a DC system, especially
with today's electronics. I was reading a while back about some
extremely high voltage DC systems used for transferring power from one
AC system to another. Pretty complicated rectifying and inverting
stations, large and expensive, along with some pretty fancy breakers
with systems to extinguish the arc when the breaker blows. But
apparently worth it.
Eric

 

[Dan Coby]

On 7/19/2016 11:40 AM, jurb6006@gmail.com wrote:

"Edison was right: we should have a DC distribution system. But >mosfet based dc/dc converters and VFD's weren't yet invented in >Edison's time. "

It would be quite feasible today. In fact somewhere I know they did use DC, there was this story about s guy using a potato to find out the radio was plugged in backwards and that was why it did not work.

I wonder how the hell to Google that...

If you want to find out about high voltage DC transmission lines then
google for 'HVDC transmission lines'.

I have stood under the Pacific Intertie which first came online in 1970

The fact that it is a DC transmission line is very obvious by the use of
two conductor bundles instead of the usual three for AC transmission.

If you want to google about the potato, good luck with your search.

Dan

 

A guy got busted many years ago for stealing power. What he did was to lay a wire parallel to the power lines and pick it up inductively. If you know electronics you know that if anything he was increasing the efficiency of the transmission line by doing that but the court ruled that anytime you get something for nothing you are stealing.

Funny how that doesn't apply to them or the businesses that bribe them.

My Uncle and cousin tried to magnetize the electric meter to slow it down. With the electric furnace and diodes from shithouse (ESI, and we should not call it that but so what) they told me weird stuff happened. All kinds of funny noises and a few other things.

Actually DC has the advantage of not having inductive losses, and what that guy "stole" was the inductive losses. If he got any current out of it it helped them, but it did not matter.

My Uncle ? Well he was a RADAR technician in the air force and the a tech specialist for Big Blue. He saw them coming, he saw them sticking it up his ass and decided to do something about it. Grampa taught us well.

I am starting to think that with all this G3 and bluetooth ad whatever else, all the radio and TV stations and whatever, you could almost pick up enough energy from the air to run a device, or charge it. We are probably getting close to the point where an antenna could pick up enough power to slow charge something.

When I put my hand on the scope probe I almost always get more that 50 volts P-P. Not much current behind it but all this new shit runs on what, four volts ?

But then, am I stealing power and have to worry about a SWAT team breaking down the front door ?

 

[Nobody]

On Wed, 20 Jul 2016 06:41:24 -0700, jurb6006 wrote:

A guy got busted many years ago for stealing power. What he did was to lay
a wire parallel to the power lines and pick it up inductively. If you know
electronics you know that if anything he was increasing the efficiency of
the transmission line by doing that

Incorrect.

but the court ruled that anytime you get something for nothing you are
stealing.

It's stealing because it increases the amount of power the utility has to
generate.

An inefficient transformer is still a transformer. Drawing current from
the secondary increases the current in the primary.

 

"...> the transmission line by doing that

Incorrect. "

You seem to lack basic electricity. The transmission line was the primary of a transformer in series with the load. He created secondary. When that secondary is loaded the impedance of the primary is lower.

All he did was to pick up some of the loss. It would not show up on anyone's meter, nor would the power company have to generate more, in fact they would have to generate less.

If the story is in fact not a suburban legend I would have liked to argue the court case. I could make a setup to demonstrate the effect. The jury would have come out with a little bit of education.

Let me ask you this, in a basic audio power amp, how come when the outputs short in blows the main AC fuse on the PRIMARY side of the transformer ? Because when you overload the secondary the impedance of the primary drops.

Now the idea of a wire is to pass current. The better it dies that the better the wire is. Whatever losses are just lost. Resistive losses are just gone unless you can use the heat somehow, but this guy was tapping into the inductive losses.

I have alot of questions about that case and information is very sparse. First of all, how the hell did he get caught ? Did a busybody neighbor call the police because he had a wire laying on the ground ? Or did they accidentally come across it while running spectography on a 12 acre cornfield looking for a pot plant ? Or did someone know he had no electric service on the property and call the power company and say "He got lights, he got lights".

Not that I doubt it. There is a town in Ohio where someone called the police on their neighbor for having a jetski in their driveway. Ironically the name of the town is Independence. It is also known as one of the most corrupt place around, and buddy we got some corrupt towns here. Simple revenue generators, and for two or three families.

Another thing, if they pollute my property with their EMI, I have a right to tap it. If I have a crystal radio, do I owe the radio stations for the power to run it ?

Fuck them and the hearse they ride out in.

 

On Wed, 20 Jul 2016 16:08:29 -0700 (PDT), jurb6006@gmail.com wrote:

"...> the transmission line by doing that

Incorrect. "

You seem to lack basic electricity. The transmission line was the primary of a transformer in series with the load. He created secondary. When that secondary is loaded the impedance of the primary is lower.

All he did was to pick up some of the loss. It would not show up on anyone's meter, nor would the power company have to generate more, in fact they would have to generate less.

If the story is in fact not a suburban legend I would have liked to argue the court case. I could make a setup to demonstrate the effect. The jury would have come out with a little bit of education.

Let me ask you this, in a basic audio power amp, how come when the outputs short in blows the main AC fuse on the PRIMARY side of the transformer ? Because when you overload the secondary the impedance of the primary drops.

Now the idea of a wire is to pass current. The better it dies that the better the wire is. Whatever losses are just lost. Resistive losses are just gone unless you can use the heat somehow, but this guy was tapping into the inductive losses.

I have alot of questions about that case and information is very sparse. First of all, how the hell did he get caught ? Did a busybody neighbor call the police because he had a wire laying on the ground ? Or did they accidentally come across it while running spectography on a 12 acre cornfield looking for a pot plant ? Or did someone know he had no electric service on the property and call the power company and say "He got lights, he got lights".

Not that I doubt it. There is a town in Ohio where someone called the police on their neighbor for having a jetski in their driveway. Ironically the name of the town is Independence. It is also known as one of the most corrupt place around, and buddy we got some corrupt towns here. Simple revenue generators, and for two or three families.

Another thing, if they pollute my property with their EMI, I have a right to tap it. If I have a crystal radio, do I owe the radio stations for the power to run it ?

Fuck them and the hearse they ride out in.

Right now there are many sensors that are powered by radio waves. Some
charge a capacitor and transmit periodically. And there is a passive
device that looks through walls to see people by using ambient wifi
radiation. See the link:
http://spectrum.ieee.org/tech-talk/at-work/test-and-measurement/see-through-walls-by-the-glow-of-your-wifi
So if you don't want folks looking at what you do in your house you
need to disable your wifi and any wifi signals emanating close to your
house. And you can't use jammers to disable the near wifi signals
because they will just use the reflected jammer radio waves to
illuminate your activites.
Eric