Gentlemen of wisdom;



I am a licensed home inspector in North Carolina. I have 30+
years experience in electronics repair (Microwave Radio and Large System
Computer), no real experience in electrical wiring but have acquired some
knowledge.

As a licensed home inspector, I am required to report any
sub-panels that do not have neutral and ground isolated from each other in
the sub-panel.

I have questioned many electricians as to the reason behind
isolating the neutral and ground with answers ranging from “well that’s
dangerous” to “because its code”. The best answer I have found was posted
on a web site explaining the possibility of a ground fault following a
parallel path (neutral and ground wires) back to the main panel. The
objectionable current on the ground wire would ruin someone’s day by flowing
to all of the outlets along the way.

I understand that current does not follow only the least resistant path,
however the amperage in each path is inversely proportional to the
resistance. With the average 110 volt circuit run in most residences less
than 200 feet, and #14 gauge wire 2.5 ohms resistance per 1000 ft. that’s
maybe ½ ohm plus connection resistances. So if the #14 gauge wire is over
fused with a 20amp breaker, and a short to the safety ground occurs, 10 amps
run through the ground and 10 amps through the neutral. With 10amps across
½ ohm the voltage developed is 5 volts rms across the length of the run. At
this point a person would have to be standing in the tub, with copper drain
lines (most are plastic now) and licking the cover plate screw on the outlet
that should be well out of reach, to feel anything until the breaker trips.
Not likely to ruin many peoples day.

I am aware of the noise problem that can occur due to current on the safety
ground and concede that ground loops are a problem with computers, stereos,
etc.

The problem I have with this is what I see as a more hazardous
condition. Mr. Homeowner is shaving with an electric razor and one hand on
the faucet. (still see copper supply plumbing) There have been intermittent
electrical problems and the electrician’s helper Dilbert has been called to
fix the problem. Dilbert finds the neutral buss conductor connection is
corroded in the sub-panel and disconnects it to clean the wire. The 5 watt
razor is opposite 100 watt bulbs etc. in the 220 volt sub-panel. The razor
now sees voltages approaching 220 volts and goes into afterburner before
melting in the hand of Mr. Homeowner. The GFCI does nothing as current is
equal in hot and neutral.

The above scenario is one that happened to a co-worker of mine a
few years ago, with exception to the razor. He was standing beside Dilbert
when the neutral wire was disconnected. Moments later his daughter came
down from her bedroom yelling “all the lights are doing strange things and
there is a smell in the house”. The electrician’s insurance company
replaced one gas range, five VCR’s, four televisions, six clock radios, one
microwave and one DVD player.

Had the neutral and ground been bonded together in the sub-panel
the un-balance loads would have been carried by the ground wire back to the
main panel.

The reason I am sending you this is to find what is wrong with
my concern and to feel better about writing up neutral ground isolation
problems in the sub-panels, which I find all the time.



Thanks for any enlightenment you can shed on me.

Vern Heiler wrote:

So if the #14 gauge wire is over
fused with a 20amp breaker, and a short to the safety ground occurs, 10 amps
run through the ground and 10 amps through the neutral. With 10amps across
½ ohm the voltage developed is 5 volts rms across the length of the run.

It doesn't take much current to cause harm. There's a reason why GFCIs
trip around 5-6 milliamps.

Above 15.5 milliamps 99% of adult males cannot let go. 18 milliamps can
cause suffocation in adult males. Above 60 milliamps can cause
ventricular fibrillation in adults.
(http://www.bassengineering.com/E_Effect.htm)

The problem I have with this is what I see as a more hazardous
condition. Mr. Homeowner is shaving with an electric razor and one hand on
the faucet. (still see copper supply plumbing) There have been intermittent
electrical problems and the electrician’s helper Dilbert has been called to
fix the problem. Dilbert finds the neutral buss conductor connection is
corroded in the sub-panel and disconnects it to clean the wire.

Before doing this, the subpanel should have been shut off. It's the
same reason that neutrals must be pigtailed in multi-wire circuits.

Chris

"Vern Heiler" wrote in message
...
Gentlemen of wisdom;



I am a licensed home inspector in North Carolina. I have 30+
years experience in electronics repair (Microwave Radio and Large System
Computer), no real experience in electrical wiring but have acquired some
knowledge.

As a licensed home inspector, I am required to report any
sub-panels that do not have neutral and ground isolated from each other in
the sub-panel.

I have questioned many electricians as to the reason behind
isolating the neutral and ground with answers ranging from "well that's
dangerous" to "because its code". The best answer I have found was
posted on a web site explaining the possibility of a ground fault
following a parallel path (neutral and ground wires) back to the main
panel. The objectionable current on the ground wire would ruin someone's
day by flowing to all of the outlets along the way.

I understand that current does not follow only the least resistant path,
however the amperage in each path is inversely proportional to the
resistance. With the average 110 volt circuit run in most residences
less than 200 feet, and #14 gauge wire 2.5 ohms resistance per 1000 ft.
that's maybe ½ ohm plus connection resistances. So if the #14 gauge wire
is over fused with a 20amp breaker, and a short to the safety ground
occurs, 10 amps run through the ground and 10 amps through the neutral.
With 10amps across ½ ohm the voltage developed is 5 volts rms across the
length of the run. At this point a person would have to be standing in
the tub, with copper drain lines (most are plastic now) and licking the
cover plate screw on the outlet that should be well out of reach, to feel
anything until the breaker trips. Not likely to ruin many peoples day.

I am aware of the noise problem that can occur due to current on the
safety ground and concede that ground loops are a problem with computers,
stereos, etc.

The problem I have with this is what I see as a more hazardous
condition. Mr. Homeowner is shaving with an electric razor and one hand
on the faucet. (still see copper supply plumbing) There have been
intermittent electrical problems and the electrician's helper Dilbert has
been called to fix the problem. Dilbert finds the neutral buss conductor
connection is corroded in the sub-panel and disconnects it to clean the
wire. The 5 watt razor is opposite 100 watt bulbs etc. in the 220 volt
sub-panel. The razor now sees voltages approaching 220 volts and goes
into afterburner before melting in the hand of Mr. Homeowner. The GFCI
does nothing as current is equal in hot and neutral.

The above scenario is one that happened to a co-worker of mine
a few years ago, with exception to the razor. He was standing beside
Dilbert when the neutral wire was disconnected. Moments later his
daughter came down from her bedroom yelling "all the lights are doing
strange things and there is a smell in the house". The electrician's
insurance company replaced one gas range, five VCR's, four televisions,
six clock radios, one microwave and one DVD player.

Had the neutral and ground been bonded together in the
sub-panel the un-balance loads would have been carried by the ground wire
back to the main panel.

The reason I am sending you this is to find what is wrong with
my concern and to feel better about writing up neutral ground isolation
problems in the sub-panels, which I find all the time.



Thanks for any enlightenment you can shed on me.


Several OSHA safety rules for working on electrical circuits have been
violated in your descriptions..
First disconnect the power and check the circuit with a meter to insure is
not energized before beginning work.
Second, if you can't disconnect the circuit, insulate any one and yourself
from coming in contact with circuit components and if possible turn off and
lock out all equipment that may become energized. If equipment can become
energized install barriers to keep persons out of danger.
Reasons for keeping the neutral (or grounded conductor) and the equipment
grounding conductor separated on the load side of the service are explained
in many books. One reason is that the equipment grounding conductor is
designed to carry enough current for a short time (like less than 1/10
second) in order to trip the circuit breaker or open a fuse. The equipment
grounding conductors are not designed to carry current for long periods of
time under normal operating conditions.
Also, you state:
With the average 110 volt circuit run in most residences less than 200
feet, and #14 gauge wire 2.5 ohms resistance per 1000 ft. that's maybe ½
ohm plus connection resistances. So if the #14 gauge wire is over fused
with a 20amp breaker, and a short to the safety ground occurs, 10 amps run
through the ground and 10 amps through the neutral. With 10amps across ½
ohm the voltage developed is 5 volts rms across the length of the run.

The resistance of No. 14 is about 3 ohms per 1000 ft. For 200 ft. the
resistance is 3 x( 200/1000) = 0.6 ohms
The ground fault current is 110 volts / .6 = 183 amperes
This high amperage is sufficient to trip a 15 ampere circuit breaker or open
a 15 ampere fuse in time. Generally we look for five times the rating of
the circuit breaker or 75 amperes in this case.
You assumed 10 amperes fault current and this is simply incorrect.

Thanks to both you and Chris for the correction on the amount of current.
It is obvious that Dilbert needed to find a new carrier. However my concern
rests in the fact that if you have a mechanical connection you have the
opportunity for failure. The other part of the equation is the resistance
to ground of the body and other materials, like rubber sneakers, wood floor,
etc. that are so prevalent today. We have all worked on 110 circuits live
and sometimes without knowing it until a blinding spark tells you. I find
neutrals and grounds tied together all the time, usually due to handyman
wiring, but never see discolored wire or any sign of problems. Fear not, I
will continue to report the condition when I find it. It's just that I feel
I see another problem. Maybe not!
"Gerald Newton" wrote in message
...

"Vern Heiler" wrote in message
...
Gentlemen of wisdom;



I am a licensed home inspector in North Carolina. I have 30+
years experience in electronics repair (Microwave Radio and Large System
Computer), no real experience in electrical wiring but have acquired some
knowledge.

As a licensed home inspector, I am required to report any
sub-panels that do not have neutral and ground isolated from each other
in the sub-panel.

I have questioned many electricians as to the reason behind
isolating the neutral and ground with answers ranging from "well that's
dangerous" to "because its code". The best answer I have found was
posted on a web site explaining the possibility of a ground fault
following a parallel path (neutral and ground wires) back to the main
panel. The objectionable current on the ground wire would ruin someone's
day by flowing to all of the outlets along the way.

I understand that current does not follow only the least resistant path,
however the amperage in each path is inversely proportional to the
resistance. With the average 110 volt circuit run in most residences
less than 200 feet, and #14 gauge wire 2.5 ohms resistance per 1000 ft.
that's maybe ½ ohm plus connection resistances. So if the #14 gauge
wire is over fused with a 20amp breaker, and a short to the safety ground
occurs, 10 amps run through the ground and 10 amps through the neutral.
With 10amps across ½ ohm the voltage developed is 5 volts rms across the
length of the run. At this point a person would have to be standing in
the tub, with copper drain lines (most are plastic now) and licking the
cover plate screw on the outlet that should be well out of reach, to feel
anything until the breaker trips. Not likely to ruin many peoples day.

I am aware of the noise problem that can occur due to current on the
safety ground and concede that ground loops are a problem with computers,
stereos, etc.

The problem I have with this is what I see as a more hazardous
condition. Mr. Homeowner is shaving with an electric razor and one hand
on the faucet. (still see copper supply plumbing) There have been
intermittent electrical problems and the electrician's helper Dilbert has
been called to fix the problem. Dilbert finds the neutral buss conductor
connection is corroded in the sub-panel and disconnects it to clean the
wire. The 5 watt razor is opposite 100 watt bulbs etc. in the 220 volt
sub-panel. The razor now sees voltages approaching 220 volts and goes
into afterburner before melting in the hand of Mr. Homeowner. The GFCI
does nothing as current is equal in hot and neutral.

The above scenario is one that happened to a co-worker of mine
a few years ago, with exception to the razor. He was standing beside
Dilbert when the neutral wire was disconnected. Moments later his
daughter came down from her bedroom yelling "all the lights are doing
strange things and there is a smell in the house". The electrician's
insurance company replaced one gas range, five VCR's, four televisions,
six clock radios, one microwave and one DVD player.

Had the neutral and ground been bonded together in the
sub-panel the un-balance loads would have been carried by the ground wire
back to the main panel.

The reason I am sending you this is to find what is wrong with
my concern and to feel better about writing up neutral ground isolation
problems in the sub-panels, which I find all the time.



Thanks for any enlightenment you can shed on me.


Several OSHA safety rules for working on electrical circuits have been
violated in your descriptions..
First disconnect the power and check the circuit with a meter to insure is
not energized before beginning work.
Second, if you can't disconnect the circuit, insulate any one and yourself
from coming in contact with circuit components and if possible turn off
and lock out all equipment that may become energized. If equipment can
become energized install barriers to keep persons out of danger.
Reasons for keeping the neutral (or grounded conductor) and the equipment
grounding conductor separated on the load side of the service are
explained in many books. One reason is that the equipment grounding
conductor is designed to carry enough current for a short time (like less
than 1/10 second) in order to trip the circuit breaker or open a fuse.
The equipment grounding conductors are not designed to carry current for
long periods of time under normal operating conditions.
Also, you state:
With the average 110 volt circuit run in most residences less than 200
feet, and #14 gauge wire 2.5 ohms resistance per 1000 ft. that's maybe ½
ohm plus connection resistances. So if the #14 gauge wire is over fused
with a 20amp breaker, and a short to the safety ground occurs, 10 amps run
through the ground and 10 amps through the neutral. With 10amps across ½
ohm the voltage developed is 5 volts rms across the length of the run.

The resistance of No. 14 is about 3 ohms per 1000 ft. For 200 ft. the
resistance is 3 x( 200/1000) = 0.6 ohms
The ground fault current is 110 volts / .6 = 183 amperes
This high amperage is sufficient to trip a 15 ampere circuit breaker or
open a 15 ampere fuse in time. Generally we look for five times the
rating of the circuit breaker or 75 amperes in this case.
You assumed 10 amperes fault current and this is simply incorrect.

"Vern Heiler" wrote in message
...
Gentlemen of wisdom;



I am a licensed home inspector in North Carolina. I have 30+
years experience in electronics repair (Microwave Radio and Large System
Computer), no real experience in electrical wiring but have acquired some
knowledge.

As a licensed home inspector, I am required to report any
sub-panels that do not have neutral and ground isolated from each other in
the sub-panel.

I have questioned many electricians as to the reason behind
isolating the neutral and ground with answers ranging from "well that's
dangerous" to "because its code". The best answer I have found was
posted
on a web site explaining the possibility of a ground fault following a
parallel path (neutral and ground wires) back to the main panel. The
objectionable current on the ground wire would ruin someone's day by
flowing
to all of the outlets along the way.

I understand that current does not follow only the least resistant path,
however the amperage in each path is inversely proportional to the
resistance. With the average 110 volt circuit run in most residences
less
than 200 feet, and #14 gauge wire 2.5 ohms resistance per 1000 ft. that's
maybe ½ ohm plus connection resistances. So if the #14 gauge wire is
over
fused with a 20amp breaker, and a short to the safety ground occurs, 10
amps
run through the ground and 10 amps through the neutral. With 10amps
across
½ ohm the voltage developed is 5 volts rms across the length of the run.
At
this point a person would have to be standing in the tub, with copper
drain
lines (most are plastic now) and licking the cover plate screw on the
outlet
that should be well out of reach, to feel anything until the breaker
trips.
Not likely to ruin many peoples day.

I am aware of the noise problem that can occur due to current on the
safety
ground and concede that ground loops are a problem with computers,
stereos,
etc.

The problem I have with this is what I see as a more hazardous
condition. Mr. Homeowner is shaving with an electric razor and one hand
on
the faucet. (still see copper supply plumbing) There have been
intermittent
electrical problems and the electrician's helper Dilbert has been called
to
fix the problem. Dilbert finds the neutral buss conductor connection is
corroded in the sub-panel and disconnects it to clean the wire. The 5
watt
razor is opposite 100 watt bulbs etc. in the 220 volt sub-panel. The
razor
now sees voltages approaching 220 volts and goes into afterburner before
melting in the hand of Mr. Homeowner. The GFCI does nothing as current is
equal in hot and neutral.

The above scenario is one that happened to a co-worker of mine
a
few years ago, with exception to the razor. He was standing beside
Dilbert
when the neutral wire was disconnected. Moments later his daughter came
down from her bedroom yelling "all the lights are doing strange things and
there is a smell in the house". The electrician's insurance company
replaced one gas range, five VCR's, four televisions, six clock radios,
one
microwave and one DVD player.

Had the neutral and ground been bonded together in the
sub-panel
the un-balance loads would have been carried by the ground wire back to
the
main panel.

The reason I am sending you this is to find what is wrong with
my concern and to feel better about writing up neutral ground isolation
problems in the sub-panels, which I find all the time.



Thanks for any enlightenment you can shed on me.



I've known about the shock hazard, but I wanted to see if there were other
concerns so I went to UL.com for some info. Check out this:
http://www.ul.com/regulators/panelboards.pdf on page 15, paragraph 50. "If
neutrals are bonded at distribution points, the neutral currents take
parallel paths through neutral feeder conductors and metal raceways. If
neutral feed conductors are open, the full neutral current flows over the
grounded raceway or the grounding conductor system. When this happens, the
steel raceway joints and box connections overheat. This is a fire hazard"

So according to Underwriters Laboratories, there is a fire hazard in
addition to a shock hazard with having the neutral bonded to ground in a
subpanel. I think it only takes 25 - 30 milliamperes to stop a human heart.

"Vern Heiler" wrote in message
...
Gentlemen of wisdom;



I am a licensed home inspector in North Carolina. I have 30+
years experience in electronics repair (Microwave Radio and Large System
Computer), no real experience in electrical wiring but have acquired some
knowledge.

As a licensed home inspector, I am required to report any
sub-panels that do not have neutral and ground isolated from each other in
the sub-panel.

I have questioned many electricians as to the reason behind
isolating the neutral and ground with answers ranging from "well that's
dangerous" to "because its code". The best answer I have found was
posted on a web site explaining the possibility of a ground fault
following a parallel path (neutral and ground wires) back to the main
panel. The objectionable current on the ground wire would ruin someone's
day by flowing to all of the outlets along the way.

I understand that current does not follow only the least resistant path,
however the amperage in each path is inversely proportional to the
resistance. With the average 110 volt circuit run in most residences
less than 200 feet, and #14 gauge wire 2.5 ohms resistance per 1000 ft.
that's maybe ½ ohm plus connection resistances. So if the #14 gauge wire
is over fused with a 20amp breaker, and a short to the safety ground
occurs, 10 amps run through the ground and 10 amps through the neutral.
With 10amps across ½ ohm the voltage developed is 5 volts rms across the
length of the run. At this point a person would have to be standing in
the tub, with copper drain lines (most are plastic now) and licking the
cover plate screw on the outlet that should be well out of reach, to feel
anything until the breaker trips. Not likely to ruin many peoples day.

I am aware of the noise problem that can occur due to current on the
safety ground and concede that ground loops are a problem with computers,
stereos, etc.

The problem I have with this is what I see as a more hazardous
condition. Mr. Homeowner is shaving with an electric razor and one hand
on the faucet. (still see copper supply plumbing) There have been
intermittent electrical problems and the electrician's helper Dilbert has
been called to fix the problem. Dilbert finds the neutral buss conductor
connection is corroded in the sub-panel and disconnects it to clean the
wire. The 5 watt razor is opposite 100 watt bulbs etc. in the 220 volt
sub-panel. The razor now sees voltages approaching 220 volts and goes
into afterburner before melting in the hand of Mr. Homeowner. The GFCI
does nothing as current is equal in hot and neutral.

The above scenario is one that happened to a co-worker of mine
a few years ago, with exception to the razor. He was standing beside
Dilbert when the neutral wire was disconnected. Moments later his
daughter came down from her bedroom yelling "all the lights are doing
strange things and there is a smell in the house". The electrician's
insurance company replaced one gas range, five VCR's, four televisions,
six clock radios, one microwave and one DVD player.

Had the neutral and ground been bonded together in the
sub-panel the un-balance loads would have been carried by the ground wire
back to the main panel.

The reason I am sending you this is to find what is wrong with
my concern and to feel better about writing up neutral ground isolation
problems in the sub-panels, which I find all the time.



Thanks for any enlightenment you can shed on me.

The hazard with common neutral and ground in sub-panels is the possibility
that if the neutral back to the main panel is interrupted the ground
conductor will continue to carry the currrent without any obvious signs.
Should the ground conductor then develop a high resistance under these
conditions, all grounded items will develop a voltage to ground, up to 120
volts. This would be an extremely dangerous situation which is totally
avoided by simply isolating the ground and neutral.

Isolation in the main panel would also be safer in this regard, but there is
a greater hazard there that the power feed neutral may become disconnected
and having the ground available to carry the neutral current can reduce the
resulting voltage unbalance.

All code requirements are actually carefully evaluated risks, remedies, and
costs, even though it may not be readily apparent. Code violations rarely
make an installation safer or in any other way "better".

Don Young

Thanks to all. It makes me feel better about writing them up having a
better knowledge of why.

"Don Young" wrote in message
...

"Vern Heiler" wrote in message
...
Gentlemen of wisdom;



I am a licensed home inspector in North Carolina. I have 30+
years experience in electronics repair (Microwave Radio and Large System
Computer), no real experience in electrical wiring but have acquired some
knowledge.

As a licensed home inspector, I am required to report any
sub-panels that do not have neutral and ground isolated from each other
in the sub-panel.

I have questioned many electricians as to the reason behind
isolating the neutral and ground with answers ranging from "well that's
dangerous" to "because its code". The best answer I have found was
posted on a web site explaining the possibility of a ground fault
following a parallel path (neutral and ground wires) back to the main
panel. The objectionable current on the ground wire would ruin someone's
day by flowing to all of the outlets along the way.

I understand that current does not follow only the least resistant path,
however the amperage in each path is inversely proportional to the
resistance. With the average 110 volt circuit run in most residences
less than 200 feet, and #14 gauge wire 2.5 ohms resistance per 1000 ft.
that's maybe ½ ohm plus connection resistances. So if the #14 gauge
wire is over fused with a 20amp breaker, and a short to the safety ground
occurs, 10 amps run through the ground and 10 amps through the neutral.
With 10amps across ½ ohm the voltage developed is 5 volts rms across the
length of the run. At this point a person would have to be standing in
the tub, with copper drain lines (most are plastic now) and licking the
cover plate screw on the outlet that should be well out of reach, to feel
anything until the breaker trips. Not likely to ruin many peoples day.

I am aware of the noise problem that can occur due to current on the
safety ground and concede that ground loops are a problem with computers,
stereos, etc.

The problem I have with this is what I see as a more hazardous
condition. Mr. Homeowner is shaving with an electric razor and one hand
on the faucet. (still see copper supply plumbing) There have been
intermittent electrical problems and the electrician's helper Dilbert has
been called to fix the problem. Dilbert finds the neutral buss conductor
connection is corroded in the sub-panel and disconnects it to clean the
wire. The 5 watt razor is opposite 100 watt bulbs etc. in the 220 volt
sub-panel. The razor now sees voltages approaching 220 volts and goes
into afterburner before melting in the hand of Mr. Homeowner. The GFCI
does nothing as current is equal in hot and neutral.

The above scenario is one that happened to a co-worker of mine
a few years ago, with exception to the razor. He was standing beside
Dilbert when the neutral wire was disconnected. Moments later his
daughter came down from her bedroom yelling "all the lights are doing
strange things and there is a smell in the house". The electrician's
insurance company replaced one gas range, five VCR's, four televisions,
six clock radios, one microwave and one DVD player.

Had the neutral and ground been bonded together in the
sub-panel the un-balance loads would have been carried by the ground wire
back to the main panel.

The reason I am sending you this is to find what is wrong with
my concern and to feel better about writing up neutral ground isolation
problems in the sub-panels, which I find all the time.



Thanks for any enlightenment you can shed on me.

The hazard with common neutral and ground in sub-panels is the possibility
that if the neutral back to the main panel is interrupted the ground
conductor will continue to carry the currrent without any obvious signs.
Should the ground conductor then develop a high resistance under these
conditions, all grounded items will develop a voltage to ground, up to 120
volts. This would be an extremely dangerous situation which is totally
avoided by simply isolating the ground and neutral.

Isolation in the main panel would also be safer in this regard, but there
is a greater hazard there that the power feed neutral may become
disconnected and having the ground available to carry the neutral current
can reduce the resulting voltage unbalance.

All code requirements are actually carefully evaluated risks, remedies,
and costs, even though it may not be readily apparent. Code violations
rarely make an installation safer or in any other way "better".

Don Young

"Vern Heiler" wrote in message
...
Thanks to all. It makes me feel better about writing them up having a
better knowledge of why.

Of equal importance to not bonding the neutral or grounded conductors on the
load side of the service is the importance of having a main bonding jumper
installed at the building service. Without the main bonding jumper a short
to ground will not trip the circuit breaker in many cases. I have found
main bonding jumpers missing in several inspections.
Let me give you a real life example that happened a Chena Hot Springs Resort
near Fairbanks, Alaska in about 1990 that almost got me killed.
A competent(?) master electrician had wired an 8 plex and I was performing
the final inspection. There was no rough in inspection since we don't have
State building permits here and I was the State Inspector. The building was
supplied from a generator at 240/120 volts located about 600 feet from the
building through an underground service lateral.
While preparing to write my inspection report I laid my metal tablet on the
Kitchen range of one unit. As I picked it up I accidentally placed my other
hand on the adjacent metal sink and received a jolt. I said what goes here?
I got my meter out of the car and checked and found 120 volts between the
range and the metal sink. Holy, mcMoley, I had just inspected the crawl
space and literal wrapped myself around metal pipes while crawling around.
I went to the service panel and checked there and again there was 120 volts
from ground to the neutral. The ranges had been grounded using the neutral
or grounded conductor and not the equipment grounding conductor as now
required. I had the master electrician come over to the open service panel
and asked him for a short piece of wire. I used the wire to temporarily
short the neutral bar to ground and whammo, a 20 ampere circuit breaker
popped. That 20 ampere circuit breaker fed a small water pump in the crawl
space. We went to it and found that the cover had pinched a hot wire to the
metal ground placing all the metal water pipes in the building at 120 volts
to whatever. We went back to the panel and sure enough the main bonding
jumper was missing. It was just a green screw that made the neutral bus
bond to the panel metal can and equipment grounding conductor.
There was a ground rod and it was bonded to the metal pipes and to the
equipment grounding bus in the service panel. Without the main bonding
jumper the fault current had to go through earth all the way to the
generator building to trip the circuit breaker and the ground resistance was
simply too high. The result was there was 120 volts potential between every
range and every metal sink in the entire building. The conclusion of this
is to never assume anything about the main bonding jumper. It is the first
thing I learned to look for when performing an inspection. Luckily, I lived
to tell this story.

On Tue, 6 Feb 2007 17:06:56 -0500, "Vern Heiler"
wrote:

Gentlemen of wisdom;



I am a licensed home inspector in North Carolina. I have 30+
years experience in electronics repair (Microwave Radio and Large System
Computer), no real experience in electrical wiring but have acquired some
knowledge.

As a licensed home inspector, I am required to report any
sub-panels that do not have neutral and ground isolated from each other in
the sub-panel.

I have questioned many electricians as to the reason behind
isolating the neutral and ground with answers ranging from “well that’s
dangerous” to “because its code”. The best answer I have found was posted
on a web site explaining the possibility of a ground fault following a
parallel path (neutral and ground wires) back to the main panel. The
objectionable current on the ground wire would ruin someone’s day by flowing
to all of the outlets along the way.

I understand that current does not follow only the least resistant path,
however the amperage in each path is inversely proportional to the
resistance. With the average 110 volt circuit run in most residences less
than 200 feet, and #14 gauge wire 2.5 ohms resistance per 1000 ft. that’s
maybe ½ ohm plus connection resistances. So if the #14 gauge wire is over
fused with a 20amp breaker, and a short to the safety ground occurs, 10 amps
run through the ground and 10 amps through the neutral. With 10amps across
½ ohm the voltage developed is 5 volts rms across the length of the run. At
this point a person would have to be standing in the tub, with copper drain
lines (most are plastic now) and licking the cover plate screw on the outlet
that should be well out of reach, to feel anything until the breaker trips.
Not likely to ruin many peoples day.

I am aware of the noise problem that can occur due to current on the safety
ground and concede that ground loops are a problem with computers, stereos,
etc.

The problem I have with this is what I see as a more hazardous
condition. Mr. Homeowner is shaving with an electric razor and one hand on
the faucet. (still see copper supply plumbing) There have been intermittent
electrical problems and the electrician’s helper Dilbert has been called to
fix the problem. Dilbert finds the neutral buss conductor connection is
corroded in the sub-panel and disconnects it to clean the wire. The 5 watt
razor is opposite 100 watt bulbs etc. in the 220 volt sub-panel. The razor
now sees voltages approaching 220 volts and goes into afterburner before
melting in the hand of Mr. Homeowner. The GFCI does nothing as current is
equal in hot and neutral.

The above scenario is one that happened to a co-worker of mine a
few years ago, with exception to the razor. He was standing beside Dilbert
when the neutral wire was disconnected. Moments later his daughter came
down from her bedroom yelling “all the lights are doing strange things and
there is a smell in the house”. The electrician’s insurance company
replaced one gas range, five VCR’s, four televisions, six clock radios, one
microwave and one DVD player.

Had the neutral and ground been bonded together in the sub-panel
the un-balance loads would have been carried by the ground wire back to the
main panel.

The reason I am sending you this is to find what is wrong with
my concern and to feel better about writing up neutral ground isolation
problems in the sub-panels, which I find all the time.



There are no 100% perfect ground systems that address every concern.

It is interesting that there is such a variation in grounding (or
earthing) systems throughout the world. Each system is a matter of
tradeoffs and compromises. Wikipedia has a good article that
describes some of the tradeoffs.

http://en.wikipedia.org/wiki/Grounding_system

Note the US and Canada use the TN-C-S scheme. The UK has both the
TN-C-S and the older TN-S system. France, always different, uses the
TT system that requires a special device called a Residual Current
Detector for safety.

In the US system, the idea is that current should never flow on the
safety ground conductor except under fault conditions. If there is a
fault, the magnitude of the current should be such that it A) it is
sufficient enough to trip out the breaker or fuse or B) trip out the
GFI.

Bonding a subpanel to a neutral means that part of the neutral return
current could flow in the protective safety ground conductor, or a
water or gas pipe, or a heating duct, or the ground itself. This is
never a good idea. Why? Well one reason is that wherever there is
current flow, there can be a potential difference between two points
that are supposed to be at the same (ground) potential. This is
dangerous and presents an electrocution hazard.

The US system is also based on the assumption that the probability of
a neutral wire opening up is relatively low. This would cause a
severe shock hazard for certain 220V appliances such as a range or
dryer wired with the older 3 wire plugs. In such a case, the frame of
the appliance would become energized (with respect to ground) since
most US 220V dryers (for example) have motors that run at 120V and
normally require a neutral for the return current. The new
requirement is a 4 wire plug and a safety ground connected to the
frame of the appliance (as I'm sure you know).

Beachcomber

"Gerald Newton" wrote in message
...

"Vern Heiler" wrote in message
...
Thanks to all. It makes me feel better about writing them up having a
better knowledge of why.

Of equal importance to not bonding the neutral or grounded conductors on
the load side of the service is the importance of having a main bonding
jumper installed at the building service. Without the main bonding jumper
a short to ground will not trip the circuit breaker in many cases. I have
found main bonding jumpers missing in several inspections.
Let me give you a real life example that happened a Chena Hot Springs
Resort near Fairbanks, Alaska in about 1990 that almost got me killed.
A competent(?) master electrician had wired an 8 plex and I was performing
the final inspection. There was no rough in inspection since we don't
have State building permits here and I was the State Inspector. The
building was supplied from a generator at 240/120 volts located about 600
feet from the building through an underground service lateral.
While preparing to write my inspection report I laid my metal tablet on
the Kitchen range of one unit. As I picked it up I accidentally placed my
other hand on the adjacent metal sink and received a jolt. I said what
goes here? I got my meter out of the car and checked and found 120 volts
between the range and the metal sink. Holy, mcMoley, I had just inspected
the crawl space and literal wrapped myself around metal pipes while
crawling around. I went to the service panel and checked there and again
there was 120 volts from ground to the neutral. The ranges had been
grounded using the neutral or grounded conductor and not the equipment
grounding conductor as now required. I had the master electrician come
over to the open service panel and asked him for a short piece of wire. I
used the wire to temporarily short the neutral bar to ground and whammo, a
20 ampere circuit breaker popped. That 20 ampere circuit breaker fed a
small water pump in the crawl space. We went to it and found that the
cover had pinched a hot wire to the metal ground placing all the metal
water pipes in the building at 120 volts to whatever. We went back to the
panel and sure enough the main bonding jumper was missing. It was just a
green screw that made the neutral bus bond to the panel metal can and
equipment grounding conductor.
There was a ground rod and it was bonded to the metal pipes and to the
equipment grounding bus in the service panel. Without the main bonding
jumper the fault current had to go through earth all the way to the
generator building to trip the circuit breaker and the ground resistance
was simply too high. The result was there was 120 volts potential between
every range and every metal sink in the entire building. The conclusion
of this is to never assume anything about the main bonding jumper. It is
the first thing I learned to look for when performing an inspection.
Luckily, I lived to tell this story.
I should have added that the service lateral from the generator was three
wire with no equipment grounding conductor.

Gerald Newton wrote:

"Gerald Newton" wrote in message
...

"Vern Heiler" wrote in message
. ..

Thanks to all. It makes me feel better about writing them up having a
better knowledge of why.


Of equal importance to not bonding the neutral or grounded conductors on
the load side of the service is the importance of having a main bonding
jumper installed at the building service. Without the main bonding jumper
a short to ground will not trip the circuit breaker in many cases. I have
found main bonding jumpers missing in several inspections.
Let me give you a real life example that happened a Chena Hot Springs
Resort near Fairbanks, Alaska in about 1990 that almost got me killed.
A competent(?) master electrician had wired an 8 plex and I was performing
the final inspection. There was no rough in inspection since we don't
have State building permits here and I was the State Inspector. The
building was supplied from a generator at 240/120 volts located about 600
feet from the building through an underground service lateral.
While preparing to write my inspection report I laid my metal tablet on
the Kitchen range of one unit. As I picked it up I accidentally placed my
other hand on the adjacent metal sink and received a jolt. I said what
goes here? I got my meter out of the car and checked and found 120 volts
between the range and the metal sink. Holy, mcMoley, I had just inspected
the crawl space and literal wrapped myself around metal pipes while
crawling around. I went to the service panel and checked there and again
there was 120 volts from ground to the neutral. The ranges had been
grounded using the neutral or grounded conductor and not the equipment
grounding conductor as now required. I had the master electrician come
over to the open service panel and asked him for a short piece of wire. I
used the wire to temporarily short the neutral bar to ground and whammo, a
20 ampere circuit breaker popped. That 20 ampere circuit breaker fed a
small water pump in the crawl space. We went to it and found that the
cover had pinched a hot wire to the metal ground placing all the metal
water pipes in the building at 120 volts to whatever. We went back to the
panel and sure enough the main bonding jumper was missing. It was just a
green screw that made the neutral bus bond to the panel metal can and
equipment grounding conductor.
There was a ground rod and it was bonded to the metal pipes and to the
equipment grounding bus in the service panel. Without the main bonding
jumper the fault current had to go through earth all the way to the
generator building to trip the circuit breaker and the ground resistance
was simply too high. The result was there was 120 volts potential between
every range and every metal sink in the entire building. The conclusion
of this is to never assume anything about the main bonding jumper. It is
the first thing I learned to look for when performing an inspection.
Luckily, I lived to tell this story.

I should have added that the service lateral from the generator was three
wire with no equipment grounding conductor.


Many people probably don't know a major function of a ground wire is to
cause enough current to flow when hot faults to ground to trip a
breaker. This requires the neutral-ground bond at the service to give a
low resistance path back to the transformer. If not bonded, the current
flows through the earth back to the transformer. The resistance will
very likely be too high to trip breakers.

--
bud--