The cable guy pointed out that I had about 5.5 amps of current going through
the grounding rod outside my home.

Wondering if this was connected to the flickering light problem I had I
called the electric company (who I must say got right on it in 3 hours).

The wires from the pole coming to the house were rubbing against the tree in
the front yard. The neutral from the pole was virtually cut.

The current in my ground wire as I understand it resulted from the current
going through either of the two hot legs of the 220 to the neutral in the
circuit box that is attached to the neutral coming in from the pole. As
this was cut, the current instead flowed to the ground rod outside (the box
is also grounded to the plumbing system).

My question is: I guess neutral and ground are joined on the neutral bar in
the circuit box. Why goes not the current always flow to ground? WHat am
I forgetting from my ancient BSEE degree?

Also does this mean when I was checking the ground wire of the cable system
(were it is lugged to the ground wire on the way to the ground rod) could I
have fried myself?

From: "new"


The cable guy pointed out that I had about 5.5 amps of current going through
the grounding rod outside my home.

Wondering if this was connected to the flickering light problem I had I
called the electric company (who I must say got right on it in 3 hours).

The wires from the pole coming to the house were rubbing against the tree in
the front yard. The neutral from the pole was virtually cut.

Hopefully, they replaced this "neutral from the pole" as it's usually also the
guy wire supporting the 2 hots.



The current in my ground wire as I understand it resulted from the current
going through either of the two hot legs of the 220 to the neutral in the
circuit box that is attached to the neutral coming in from the pole. As
this was cut, the current instead flowed to the ground rod outside (the box
is also grounded to the plumbing system).

My question is: I guess neutral and ground are joined on the neutral bar in
the circuit box. Why goes not the current always flow to ground? WHat am
I forgetting from my ancient BSEE degree?

What you are forgetting is that ground is for safety, in this case a redundant
backup in the event something just like this happens.

You're also forgetting, utilities don't deal with "neutrals" in the sense that
inside wiremen do - for a utility system there is no "neutral," they call that
conductor just ground. It only becomes a neutral after it has joined with your
ground rod in your main panel.

The current doesn't normally just go to ground (from your panel's neutral buss
bar to your grounding rod and/or water main) because it's easier, and usually a
shorter trip, to get back to exactly where it came from (the utility's
transformer, where their "neutral," - the center tap) via the guy wire. That's
supposed to be the path of least resistance. Without it, all of your home's
unbalanced load would have to flow through your ground rod, into the ground and
make either a b-line toward the transformer's ground rod (If it's present and
maintained) or, to the next home's ground rod, into their panel's neutral buss
and back through their intact guy wire.

Or then again, since you can't tell which way the AC is flowing on your 5.5 amp
reading, perhaps it's your neighbor who has a bad neutral...

Also does this mean when I was checking the ground wire of the cable system
(were it is lugged to the ground wire on the way to the ground rod) could I
have fried myself?

You could have, if that was the path taken by your, or someone else's
unbalanced load.

According to HA HA Budys Here :
From: "new"
The current in my ground wire as I understand it resulted from the current
going through either of the two hot legs of the 220 to the neutral in the
circuit box that is attached to the neutral coming in from the pole. As
this was cut, the current instead flowed to the ground rod outside (the box
is also grounded to the plumbing system).

My question is: I guess neutral and ground are joined on the neutral bar in
the circuit box. Why goes not the current always flow to ground? WHat am
I forgetting from my ancient BSEE degree?

You're also forgetting, utilities don't deal with "neutrals" in the sense that
inside wiremen do - for a utility system there is no "neutral," they call that
conductor just ground. It only becomes a neutral after it has joined with your
ground rod in your main panel.

Taking the terms in the standards literally, it's the reverse of that. Neutrals
are effectively the "centre reference" of a multiple wire circuit. Ie: three
phase. Ie: the neutral of the 220 split phase circuit that's your house feed.

"Real" Neutrals aren't necessarily anywhere _near_ ground.

Technically, for example, a 120V circuit cannot have a neutral because it's
not a multi-wire circuit.

Once the neutral comes to your panel, it becomes the "grounded conductor" because
it's connected to ground. As contrasted with the "grounding conductor"
(safety ground).

The electrical codes (both NEC and CEC) very specifically uses the "grounded
conductor" term instead of "neutral" for the white wiring in your house.

However, the home building trade uses the word neutral. So do most others, despite
the fact that the terminology isn't technically accurate.

[There's a longer explanation in the electrical wiring FAQ which specifically
uses "neutral" to be consistent with the majority of usage, and make it very
difficult to confuse it with "grounding conductor"]

The current doesn't normally just go to ground (from your panel's neutral buss
bar to your grounding rod and/or water main) because it's easier, and usually a
shorter trip, to get back to exactly where it came from (the utility's
transformer, where their "neutral," - the center tap) via the guy wire.

"shorter trip", being short form for "lowest resistance".

Most people tend to think that grounding rods and the like have very
low resistance (as in zero). They do not. The grounding-rod to dirt resistance
can be surprisingly high. For example, a NEC-satisfactory grounding system
can have _more_ than 25 ohms to dirt. A dead-short to dirt could
only push 5A or so at 120V. Not even enough to trip the breaker.

Grounding systems aren't supposed to carry current. They're really only
a secondary way to keep the power from drifting too far away from a dirt
reference. Neutral current (the imbalance between the currents of the two
hot wires) is _supposed_ to go down the real neutral wire back to the
transformer.

Trying to make the dirt be a conductor can lead to all sorts of problems -
highly variable voltage (especially under variable loads), electrical
shocks from standing on the dirt, setting the grass on fire. Etc.

If you see appreciable current flow in the grounding conductor, it almost
always means that there's something wrong with the neutral. Which implies
the "loose neutral" syndrome, where you can get wild voltage swings on 120V
circuits. Including up to 220V...

Or then again, since you can't tell which way the AC is flowing on your 5.5 amp
reading, perhaps it's your neighbor who has a bad neutral...

Unlikely. The range is relatively short, and you're only getting "side
effects" of a situation which'd be _far_ worse in the neighbor's. Ie:
exploding TV sets. Ie: high voltages on grounded appliance cases or
plumbing.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

Great answers guys - you are right ground does not equal neutral - I even
remember being taught that!

new wrote:
Great answers guys - you are right ground does not equal neutral - I even
remember being taught that!
Hi,
Ground = safety, last defense line.
Ground loop causes undesirable ground current in many instances.
Tony

Hey Chris Lewis, I miss your every-so-often posting of wiring info,
FAQ, whatever you called it.
Perhaps you could post the link to it every few months with a brief
description of what it is -- for the new readers. --Phil

Chris Lewis wrote:

...
--
Phil Munro Dept of Electrical & Computer Engin
Youngstown State University
Youngstown, Ohio 44555

In article , (Chris Lewis) wrote:
Most people tend to think that grounding rods and the like have very
low resistance (as in zero). They do not. The grounding-rod to dirt
resistance
can be surprisingly high. For example, a NEC-satisfactory grounding system
can have _more_ than 25 ohms to dirt. A dead-short to dirt could
only push 5A or so at 120V. Not even enough to trip the breaker.

I believe the NEC recommends driving a second ground rod, if the first
measures more that 25 ohms. I can't remember if you are supposed to do
anything else if you still have over 25 ohms.

In telephony-land, cell sites usually are required to have 5 ohms or less. Of
course,they come with 100 ft+ lightning rod, known as the cell tower. :-)

-don

According to Phil Munro :
Hey Chris Lewis, I miss your every-so-often posting of wiring info,
FAQ, whatever you called it.
Perhaps you could post the link to it every few months with a brief
description of what it is -- for the new readers. --Phil

The machine that we run the FAQ posting stuff on has lost access all but a very
small number of Usenet groups. None of which are in common with the groups
the FAQ was posting to, hence it wasn't working for quite a long time.

H'm, maybe it does work. Stay tuned.

If not, google for "Electrical Wiring FAQ". There are links _everywhere_.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

new wrote:

Great answers guys - you are right ground does not equal neutral - I even
remember being taught that!

Hi,
Ground = safety, last defense line.
Ground loop causes undesirable ground current in many instances.
Tony


Tony
Are you lost, just quarrelsome or both. Have you ever actually measured
a ground loop current in access of one amp. Natural ground gradients
never produce currents of 5.5 amperes. Ground loops occur from voltage
gradients that are measured in millivolts. The only hazard a naturally
occurring ground loop causes is to electronic signal quality between
digital equipment connected to grounds with differing potentials.

250.4 General Requirements for Grounding and Bonding.

The following general requirements identify what grounding and bonding
of electrical systems are required to accomplish. The prescriptive
methods contained in Article 250 shall be followed to comply with the
performance requirements of this section.

(A) Grounded Systems.

(1) Electrical System Grounding. Electrical systems that are grounded
shall be connected to earth in a manner that will limit the voltage
imposed by lightning, line surges, or unintentional contact with
higher-voltage lines and that will stabilize the voltage to earth during
normal operation.


The actual grounding of electric systems is not done for electrical
safety but rather for limiting damage to the system from "lightning,
line surges, or unintentional contact with higher-voltage lines."

The conductors that actually provide a safe level of touch potential on
the exposed non current carrying metallic parts of the wiring system are
called Equipment Grounding Conductors because they connect the exposed
metallic parts to the Grounding Electrode Conductor. The connection
that actually clears any fault is the main bonding jumper. That conducts
the stray current back to the neutral of the service and to the Xo of
the transformer. If the fault that is allowing the current to get into
the exposed metallic parts in the first place is of a low enough
impedance sufficient current flows to trip the Over Current Protective
Device. If the fault impedance is too high for this then the low
impedance pathway provided by the EGCs keeps the touch potential below
dangerous levels.
--
Tom

According to Postmaster :

Are you lost, just quarrelsome or both. Have you ever actually measured
a ground loop current in access of one amp. Natural ground gradients
never produce currents of 5.5 amperes. Ground loops occur from voltage
gradients that are measured in millivolts. The only hazard a naturally
occurring ground loop causes is to electronic signal quality between
digital equipment connected to grounds with differing potentials.

Two comments:

1) Ground loops cause the flow of continuous current from one place to another,
usually including one or more "sub-optimal" connections. Ie: buried/wet.
Which can lead to galvanic corrosion and connection failure. Even if the
current flow is very low...

2) It's not just "natural" ground gradients you need to worry about.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

On 10/27/03 7:44 PM, in article ,
"new" wrote:

The cable guy pointed out that I had about 5.5 amps of current going through
the grounding rod outside my home.

Wondering if this was connected to the flickering light problem I had I
called the electric company (who I must say got right on it in 3 hours).

The wires from the pole coming to the house were rubbing against the tree in
the front yard. The neutral from the pole was virtually cut.

The current in my ground wire as I understand it resulted from the current
going through either of the two hot legs of the 220 to the neutral in the
circuit box that is attached to the neutral coming in from the pole. As
this was cut, the current instead flowed to the ground rod outside (the box
is also grounded to the plumbing system).

My question is: I guess neutral and ground are joined on the neutral bar in
the circuit box. Why goes not the current always flow to ground? WHat am
I forgetting from my ancient BSEE degree?

Also does this mean when I was checking the ground wire of the cable system
(were it is lugged to the ground wire on the way to the ground rod) could I
have fried myself?


Doesn't Kirchoff's Law have something to do with this even if the
"neutral" is good? On a 3 wire service the ground rods and the earth will
form a parallel path with the neutral and there will be a small amount of
current flowing through the rods.
I know livestock operations had some problems with transient voltage with
3 wire hookups. Four wire hookups are recommended now for things like
milking barns etc.

Dean



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According to Dean Hoffman :
Also does this mean when I was checking the ground wire of the cable system
(were it is lugged to the ground wire on the way to the ground rod) could I
have fried myself?

Doesn't Kirchoff's Law have something to do with this even if the
"neutral" is good? On a 3 wire service the ground rods and the earth will
form a parallel path with the neutral and there will be a small amount of
current flowing through the rods.

Absolutely true. But consider: ground rod connectivity isn't that good
usually.

Do the calculations - if the ground rod to dirt resistance is, say, 25 ohms
[permissible in the NEC], and the neutral wire resistance is, say, .1 ohms
(which is probably much higher than it should be), what would the neutral
wire current be for the ground rod current to be 5.5A? Secondly, what would
the voltage on the grounding system (eg: your plumbing, appliance
cases etc) be relative to dirt?

Something on the order of 1400A (the service wires will melt) and 120V
(danger! danger! don't touch that pipe!) respectively.

Measureable current through ground over a few milliamps means
there's a problem. High current guarantees there's something
VERY wrong with the neutral or something else major.