I have a fundamental electrical question. I have several years old
Siemens 150 A main panel that has single neutral/ground terminal. All
ground and neutral wires are attached to it. There are also only three
incoming wires into the panel: two 220V hot wires and one ground wire.
So what I see there is no difference between ground and neutral wire so
the questions is why wiring is done with three wires instead of two? Is
it possible (legal) to connect ground and neutral wire together in a
switch box? As far as I understand from books I read most panels have
only single neutral/ground terminal.

"Sasha" wrote in message
oups.com...
I have a fundamental electrical question. I have several years old
Siemens 150 A main panel that has single neutral/ground terminal. All
ground and neutral wires are attached to it. There are also only three
incoming wires into the panel: two 220V hot wires and one ground wire.
So what I see there is no difference between ground and neutral wire so
the questions is why wiring is done with three wires instead of two? Is
it possible (legal) to connect ground and neutral wire together in a
switch box? As far as I understand from books I read most panels have
only single neutral/ground terminal.

There are many on this group that will be able to give you a more technical
explanation, but my understanding is that most residential main panels have
the service entrance come with the two hot wires, one ground, and the
neutral / ground bar is shared. Note: to meet code, the main panel should
be grounded to the water pipe and to a grounding rod as I understand it.
You might have missed them as they are smaller (than the service 00 or
larger gauge) bare 4-6 gauge wires that should exit the panel to the
locations I just stated.

I do not think it is legal or safe to combine the ground and neutral
together in a switch box, but I am not an electrician.

There are times when the ground and neutral bars are separated, such as the
installation of a subpanel, the ground and neutral are separated in this
load center.

Hope this helps, and I am sure more will respond.

David

Sasha wrote:
I have a fundamental electrical question. I have several years old
Siemens 150 A main panel that has single neutral/ground terminal. All
ground and neutral wires are attached to it. There are also only three
incoming wires into the panel: two 220V hot wires and one ground wire.
So what I see there is no difference between ground and neutral wire
so the questions is why wiring is done with three wires instead of
two? Is it possible (legal) to connect ground and neutral wire
together in a switch box? As far as I understand from books I read
most panels have only single neutral/ground terminal.

The ground wire and neutral wire in a residential electrical
system should be connected together at one -- and only one --
point in the system: where the service enters the house. Thus,
if you have a 220V service, your service entry panel will have
two hot wires and a neutral coming from the utility company.
The panel will be grounded to earth. At that point, the
neutral is connected to ground.

Connecting the neutral and ground together anywhere else but
the entry service could result in a potential difference across the
ground wires throughout the system in case of a short -- a
dangerous situation.

Could you explain to me why connecting ground and neutral wire
"anywhere else but the entry service could result in a potential
difference across the ground wires throughout the system in case of a
short -- a dangerous situation"? They are connected in main panel? What
"dangerous situation" can it be if neutral and ground wires are
connected somewhere up in circuits? Also I checked my service which is
three years old and was done by license electrician has only three
incoming wires - there are no separate ground and neutral wire, just
one thick white wire connected to neutral/ground terminal.

In article . com, "Sasha" wrote:
Could you explain to me why connecting ground and neutral wire
"anywhere else but the entry service could result in a potential
difference across the ground wires throughout the system in case of a
short -- a dangerous situation"?

The neutral wire carries current, in normal operation. The ground wire does
*not*.

Having these two connected anywhere except the service entrance panel results
in current being present on the ground wire as well as the neutral - which in
turn electrifies *every* metal fixture box, *every* metal appliance chassis,
*every* plumbing fixture, etc. throughout the house.


They are connected in main panel?

Yes, and at the main panel, they are *also* connected to a grounding electrode
to ensure that both are at true ground potential _at_the_panel_.

What
"dangerous situation" can it be if neutral and ground wires are
connected somewhere up in circuits?

See above.

Also I checked my service which is
three years old and was done by license electrician has only three
incoming wires - there are no separate ground and neutral wire, just
one thick white wire connected to neutral/ground terminal.

Three wires coming in from the power company, yes. There should also be a
fairly heavy gauge bare (or green insulated) wire connected to the
neutral/ground bus bar in the panel, that is connected at its other end to a
grounding rod sunk into the earth outside the house and very close to the
service entrance.


--
Regards,
Doug Miller (alphageek at milmac dot com)

Nobody ever left footprints in the sands of time by sitting on his butt.
And who wants to leave buttprints in the sands of time?

The ground is properly called a "grounding" conductor and the neutral is a
"grounded" conductor. (except for 240v, where there really is a neutral,
but lets not go there)

As the names imply, they got to ground; in fact, they meet up at the breaker
box and go to ground together. However, they serve completely different
purposes.

The grounded conductor is the return path for the electricity. The
grounding conductor is a safety path it prevent exposed surfaces from being
energized in event of a short. You could do as you suggest; use the
grounded conductor as a grounding conductor as well; in fact, older dryers
and ovens essentially do that. But it is potentially unsafe; if the
grounded conductor was broken, anyone touching the oven works as the
grounded conductor. A separate grounding conductor prevents that. If the
two wires are connected anywhere but the breaker box, then they are the same
wire and the redundency is somewhat lost. (please excuse me if I got my
"ing" and "ed" mixed up somewhere; you see why they are popularly called
ground and neutral.)

If you are still interested in the subject, do a search on "ground loops".
I don't actually understand it, and really don't want to.

You are assuming wire is electrically same at both ends.
Not true. As wire carries more current, then those electrical
differences become more obvious. Others will provide (and
have previously posted) why these neutral and safety ground
wires remain separate. However underlying all those reasons
is one fact: wires are electrically different at their
opposite ends. When measured, those differences were not
detectable for electrical reasons. Connect a major load such
as a steam iron to that circuit. Then take those voltage
measurements again.

That single neutral ground bus bar is the central safety
ground that every building must contain for specific safety
reasons.

Sasha wrote:
I have a fundamental electrical question. I have several years old
Siemens 150 A main panel that has single neutral/ground terminal. All
ground and neutral wires are attached to it. There are also only three
incoming wires into the panel: two 220V hot wires and one ground wire.
So what I see there is no difference between ground and neutral wire so
the questions is why wiring is done with three wires instead of two? Is
it possible (legal) to connect ground and neutral wire together in a
switch box? As far as I understand from books I read most panels have
only single neutral/ground terminal.

In article , "toller" wrote:
The ground is properly called a "grounding" conductor and the neutral is a
"grounded" conductor. (except for 240v, where there really is a neutral,
but lets not go there)

Try again... in a 240V circuit there is *NOT* a neutral.

I don't actually understand it, and really don't want to.

One wonders why you felt compelled to post...

--
Regards,
Doug Miller (alphageek at milmac dot com)

Nobody ever left footprints in the sands of time by sitting on his butt.
And who wants to leave buttprints in the sands of time?

Sasha wrote:
Could you explain to me why connecting ground and neutral wire
"anywhere else but the entry service could result in a potential
difference across the ground wires throughout the system in case of a
short -- a dangerous situation"? They are connected in main panel? What
"dangerous situation" can it be if neutral and ground wires are
connected somewhere up in circuits? Also I checked my service which is
three years old and was done by license electrician has only three
incoming wires - there are no separate ground and neutral wire, just
one thick white wire connected to neutral/ground terminal.


If you cross connect the grounding terminal of a three wire receptacle
to the neutral than any failure of the neutrals continuity will cause
the conductive casing of any appliance or tool that was plugged into
that receptacle to become energized at 120 volts relative to any
grounded object. When a human being comes into contact with that
energized surface then a painful and possibly fatal shock occurs. If
they are also in contact with a grounded surface then the shock is
nearly always injurious or fatal.

With a circuit that includes a Equipment Grounding (bonding) Conductor
(EGC) the failure of continuity of the insulated current carrying
grounded conductor only causes the plugged in load to stop working.
Because there is no connection to the exposed metallic parts of the
homes systems there is still no ready way to come in contact with a
current carrying conductor and receive a shock. The EGC insures that
any fault to the exposed conductive parts of the homes systems will be
connected back to the neutral of the service conductors and by that back
to the source of supply at the utilities transformer. If the fault is
in the hot conductor the bonding conductor carries enough current back
to the supply to cause the Over Current Protective Device (OCPD) to open
and deenergize the circuit. If the fault is to the neutral conductor
the bonding conductor carries the current back to the source of supply
but since the current flow is limited by the load that current will be
less than the OCPD is designed to open. The bonding conductor will keep
the voltage on exposed conductive surfaces below dangerous levels. In
circuits protected by GFCIs, AFCIs, and Ground Fault Protection of
Equipment the fault detection will open the circuit because the current
flowing in the bonding conductor will imbalance the detector of the
fault protection device.

The neutral conductor is grounded at the building served in areas served
by a Multi Grounded Neutral (MGN) utility distribution system. MGN is
the system used in North American practice but it is not universal world
wide. There is a growing body of evidence that suggest that it is not
the safest way to distribute electricity. If an open occurs in the
utility supplied neutral conductor a dangerous voltage can exist in the
wiring system of the building served relative to the earth around it.
This becomes most obvious on buildings with metal siding and or those
with high impedance earth grounds.
--
Tom Horne


Well we aren't no thin blue heroes and yet we aren't no blackguards to.
We're just working men and woman most remarkable like you.

I see a lot of disjoint answers here. I'n no expert but what I
remember from my electrical engineering classes is that the neutral
originates from the center tap of the secondary windings of the
distribution transformer and the neutral is grounded ONLY at the
distribution transformer is not grounded elsewhere. The distribution
transformer sits either on a pole outside your house somewhere or is in
a box on the ground. Three wires come into your house: phase A hot,
phase B hot, and the neutral. The voltage from phase A to phase B hot
is 240V nominal and the voltage from either phase A or phase B to
neurtal is 120V nominal. The phase A and phase B orginate from a 3
phase system so their voltages are 120 deg out of phase with one
another.

The GROUND (bare copper wire in std electrical wiring) is grounded the
the house distribution panel and is there for safety and provides a low
resistance path to ground so shorts travel through that rather than you
to ground.

I would think that tieing gournd to neutral also could be problems
because now you are carrying current through the ground and any
resistance to ground would cause a voltage to appear which mean you
could get zapped by touching grounded junction boxes or appliances.
Maybe cause problems with GFICs as well.

In article .com, "Jerry" wrote:
I see a lot of disjoint answers here. I'n no expert but what I
remember from my electrical engineering classes is that the neutral
originates from the center tap of the secondary windings of the
distribution transformer

Yes...

and the neutral is grounded ONLY at the
distribution transformer is not grounded elsewhere.

No. It is also grounded at the service entrance panel.

The distribution
transformer sits either on a pole outside your house somewhere or is in
a box on the ground. Three wires come into your house: phase A hot,
phase B hot, and the neutral. The voltage from phase A to phase B hot
is 240V nominal and the voltage from either phase A or phase B to
neurtal is 120V nominal.

This is correct...

The phase A and phase B orginate from a 3
phase system so their voltages are 120 deg out of phase with one
another.

... but this is not. Residential service in most of North America is
*single* phase. The voltages on the two legs of a 240V residential service are
*180* degrees out of phase with each other - that's how they can maintain a
240V potential between them, while each is at 120V potential from neutral.

No disagreement with the remainder of your post.

The GROUND (bare copper wire in std electrical wiring) is grounded the
the house distribution panel and is there for safety and provides a low
resistance path to ground so shorts travel through that rather than you
to ground.

I would think that tieing gournd to neutral also could be problems
because now you are carrying current through the ground and any
resistance to ground would cause a voltage to appear which mean you
could get zapped by touching grounded junction boxes or appliances.
Maybe cause problems with GFICs as well.


--
Regards,
Doug Miller (alphageek at milmac dot com)

Nobody ever left footprints in the sands of time by sitting on his butt.
And who wants to leave buttprints in the sands of time?

Jerry wrote:
I see a lot of disjoint answers here. I'm no expert but what I
remember from my electrical engineering classes is that the neutral
originates from the center tap of the secondary windings of the
distribution transformer and the neutral is grounded ONLY at the
distribution transformer is not grounded elsewhere. The distribution
transformer sits either on a pole outside your house somewhere or is in
a box on the ground. Three wires come into your house: phase A hot,
phase B hot, and the neutral. The voltage from phase A to phase B hot
is 240V nominal and the voltage from either phase A or phase B to
neutral is 120V nominal. The phase A and phase B originate from a 3
phase system so their voltages are 120 deg out of phase with one
another.

The GROUND (bare copper wire in std electrical wiring) is grounded the
the house distribution panel and is there for safety and provides a low
resistance path to ground so shorts travel through that rather than you
to ground.

I would think that tieing ground to neutral also could be problems
because now you are carrying current through the ground and any
resistance to ground would cause a voltage to appear which mean you
could get zapped by touching grounded junction boxes or appliances.
Maybe cause problems with GFICs as well.


Jerry
Your giving bad information.

In north American practice the neutral is grounded at the transformer
and at the buildings Service Disconnecting Means. Every model electric
code requires this.

Single phase wye connected service is sometimes delivered to homes that
are served from the same transformer set as multi family dwellings or
commercial occupancies but this is done with only a very small minority
of homes.

Most, but not all, of the transformers that supply single family
detached homes are supplied from only one phase of the supply lines on
the top of the pole. In many neighborhoods only one phase of the
distribution is brought down a given street. The secondary side of the
transformer that serves any given home is center tapped in order to
derive two separate voltages from the same winding but none of those
voltages is actually out of phase with the other. Since you studied
electrical engineering you know that a transformer can have a large
number of taps on it's windings but those taps don't create different
phases only different voltages.
--
Tom Horne


Well we aren't no thin blue heroes and yet we aren't no blackguards to.
We're just working men and woman most remarkable like you.

According to Doug Miller :
In article , "toller" wrote:
The ground is properly called a "grounding" conductor and the neutral is a
"grounded" conductor. (except for 240v, where there really is a neutral,
but lets not go there)

Try again... in a 240V circuit there is *NOT* a neutral.

Right, a 240V branch circuit doesn't have a neutral.

But, the context of this thread is main panels and 240V service
entrances. A 240V service _does_ have what we call a neutral
(officially "grounded conductor") by definition.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

In article , (Chris Lewis) wrote:
According to Doug Miller :
In article , "toller"
wrote:
The ground is properly called a "grounding" conductor and the neutral is a
"grounded" conductor. (except for 240v, where there really is a neutral,
but lets not go there)

Try again... in a 240V circuit there is *NOT* a neutral.

Right, a 240V branch circuit doesn't have a neutral.

But, the context of this thread is main panels and 240V service
entrances.

No, it's not. In the original post, Sasha is clearly referring to branch
circuits when he writes:

"So what I see there is no difference between ground and neutral wire so
the questions is why wiring is done with three wires instead of two? Is
it possible (legal) to connect ground and neutral wire together in a
switch box?"

A 240V service _does_ have what we call a neutral
(officially "grounded conductor") by definition.

No argument there - but that's not what we started out talking about.

--
Regards,
Doug Miller (alphageek at milmac dot com)

Nobody ever left footprints in the sands of time by sitting on his butt.
And who wants to leave buttprints in the sands of time?

Thanks for clarifying. I was using text book stuff from years ago. I
always thought that the 240/120 1phase service was from a wye connected
transformer driven by 3phase supply. My world is semiconductors and my
voltages are all DC and 5V or less -- and it shows....