Hi all:

Six years ago, I built my workshop about 150ft from the house with a
100A service. I ran a four-conductor cable to the subpanel in the
shop, and kept the ground and neutral conductors isolated from each
other. I did not bond the sub-panel ground to its own ground rod,
thinking it might cause a ground loop and/or noise in the intercom
circuit bewteen the buildings. More recently, when I put in a spa with
it's own GFCI breaker, I had several people advise me to drive a
separate ground rod for it, and that I should have done the same for my
workshop. So far, I have had no issues, but I want to make sure I did
the right thing.

My searches here have yielded many debates on the need to keep the
ground and neutral bonded only in the main panel and not the subs
(which is how I did it), but nothing about the ground rod question.
Does a remote subpanel need its own ground rod or not?
Thanks in advance,
John.

Yup you need a ground rod and that gets connected to the ground bus, The
neutral still stays isolated

On 12 Jan 2005 12:50:24 -0800, "the_tool_man"
wrote:

Hi all:

Six years ago, I built my workshop about 150ft from the house with a
100A service. I ran a four-conductor cable to the subpanel in the
shop, and kept the ground and neutral conductors isolated from each
other. I did not bond the sub-panel ground to its own ground rod,
thinking it might cause a ground loop and/or noise in the intercom
circuit bewteen the buildings. More recently, when I put in a spa with
it's own GFCI breaker, I had several people advise me to drive a
separate ground rod for it, and that I should have done the same for my
workshop. So far, I have had no issues, but I want to make sure I did
the right thing.

My searches here have yielded many debates on the need to keep the
ground and neutral bonded only in the main panel and not the subs
(which is how I did it), but nothing about the ground rod question.

2002NEC 250.32(b)2

Paraphrase, if you have no grounding method between your main panel
and the garage panel, then you bond your sub panels grounded(neutral)
and grounding conductors in the sub panel.

Does a remote subpanel need its own ground rod or not?

2002NEC 25.32(A) Exception

Paraphase:if you have only one branch circuit supplies your subpanel,
and it has an equipment grounding conductor, then you are ok without
the ground rod.


Thanks in advance,
John.

No debate, all in black and white in the blessed book. :-P

hth,

tom @ www.FreelancingProjects.com

Would a seperate ground cause a difference of potential ? Causing a hazzard?
"the_tool_man" wrote in message
oups.com...
Hi all:

Six years ago, I built my workshop about 150ft from the house with a
100A service. I ran a four-conductor cable to the subpanel in the
shop, and kept the ground and neutral conductors isolated from each
other. I did not bond the sub-panel ground to its own ground rod,
thinking it might cause a ground loop and/or noise in the intercom
circuit bewteen the buildings. More recently, when I put in a spa with
it's own GFCI breaker, I had several people advise me to drive a
separate ground rod for it, and that I should have done the same for my
workshop. So far, I have had no issues, but I want to make sure I did
the right thing.

My searches here have yielded many debates on the need to keep the
ground and neutral bonded only in the main panel and not the subs
(which is how I did it), but nothing about the ground rod question.
Does a remote subpanel need its own ground rod or not?
Thanks in advance,
John.

"the_tool_man" wrote in message
oups.com...
Hi all:

Six years ago, I built my workshop about 150ft from the house with a
100A service. I ran a four-conductor cable to the subpanel in the
shop, and kept the ground and neutral conductors isolated from each
other. I did not bond the sub-panel ground to its own ground rod,
thinking it might cause a ground loop and/or noise in the intercom
circuit bewteen the buildings. More recently, when I put in a spa with
it's own GFCI breaker, I had several people advise me to drive a
separate ground rod for it, and that I should have done the same for my
workshop. So far, I have had no issues, but I want to make sure I did
the right thing.

My searches here have yielded many debates on the need to keep the
ground and neutral bonded only in the main panel and not the subs
(which is how I did it), but nothing about the ground rod question.
Does a remote subpanel need its own ground rod or not?
Thanks in advance,
John.


Unless you have a connection between your garage and main dwelling such as
water pipe, you need to install a ground rod for your sub panel. You don't
need to put in a ground rod to your spa.
You do, however, need to bond any grounded metal within 5' of the spa water
to the bonding lug on your spa panel, using bare solid copper.

"the_tool_man" wrote in message
oups.com...
Hi all:

Six years ago, I built my workshop about 150ft from the house with a
100A service. I ran a four-conductor cable to the subpanel in the
shop, and kept the ground and neutral conductors isolated from each
other. I did not bond the sub-panel ground to its own ground rod,
thinking it might cause a ground loop and/or noise in the intercom
circuit bewteen the buildings. More recently, when I put in a spa with
it's own GFCI breaker, I had several people advise me to drive a
separate ground rod for it, and that I should have done the same for my
workshop. So far, I have had no issues, but I want to make sure I did
the right thing.

My searches here have yielded many debates on the need to keep the
ground and neutral bonded only in the main panel and not the subs
(which is how I did it), but nothing about the ground rod question.
Does a remote subpanel need its own ground rod or not?
Thanks in advance,
John.

Supplemental grounding gets tricky pretty fast.
Excellent choice for the 4 wire service to the garage.
Now if you drive a ground rod at the garage then the grounding conductor
back to the service must be of the same size as your service ground. If not
you COULD have a problem with an fault.... note could..
As for the spa driving another ground rod is just complicating the issue. I
assume that you took a grounding conductor to the spa, if it is connected
correctly you do not need a ground rod there.
Try reading the Soars book on Grounding. Lots of pictures and easy text to
understand.
Heck I probably do not understand what your doing cause I can not see it.

Since you ran a grounding conductor with the feed to the subpanel, you do
not need to install a ground rod at that location.

If you feel the need to install a ground rod it should be at the main panel.
What is your current main ground?


John Grabowski
http://www.mrelectrician.tv



"the_tool_man" wrote in message
oups.com...
Hi all:

Six years ago, I built my workshop about 150ft from the house with a
100A service. I ran a four-conductor cable to the subpanel in the
shop, and kept the ground and neutral conductors isolated from each
other. I did not bond the sub-panel ground to its own ground rod,
thinking it might cause a ground loop and/or noise in the intercom
circuit bewteen the buildings. More recently, when I put in a spa with
it's own GFCI breaker, I had several people advise me to drive a
separate ground rod for it, and that I should have done the same for my
workshop. So far, I have had no issues, but I want to make sure I did
the right thing.

My searches here have yielded many debates on the need to keep the
ground and neutral bonded only in the main panel and not the subs
(which is how I did it), but nothing about the ground rod question.
Does a remote subpanel need its own ground rod or not?
Thanks in advance,
John.

SQLit wrote:
"the_tool_man" wrote in message
oups.com...

Hi all:

Six years ago, I built my workshop about 150ft from the house with
a 100A service. I ran a four-conductor cable to the subpanel in
the shop, and kept the ground and neutral conductors isolated from
each other. I did not bond the sub-panel ground to its own ground
rod, thinking it might cause a ground loop and/or noise in the
intercom circuit bewteen the buildings. More recently, when I put
in a spa with it's own GFCI breaker, I had several people advise me
to drive a separate ground rod for it, and that I should have done
the same for my workshop. So far, I have had no issues, but I want
to make sure I did the right thing.

My searches here have yielded many debates on the need to keep the
ground and neutral bonded only in the main panel and not the subs
(which is how I did it), but nothing about the ground rod question.
Does a remote subpanel need its own ground rod or not? Thanks in
advance, John.


Supplemental grounding gets tricky pretty fast. Excellent choice for
the 4 wire service to the garage. Now if you drive a ground rod at
the garage then the grounding conductor back to the service must be
of the same size as your service ground. If not you COULD have a
problem with an fault.... note could..

If he ran a 100A feeder to the garage panel, the grounding wire is at
least 6 gauge, and maybe 4. IIRC, #6 is the largest wire you are ever
required to use to connect a ground rod to the grounding electrode system.

I would probably drive a ground rod at the garage. I don't know if it
is required or not (but I think it is.) Since there's a seperate
grounding wire already, I don't think it's all that important.

Bob

On Wed, 12 Jan 2005 19:46:39 -0600, zxcvbob
wrote:

SQLit wrote:
"the_tool_man" wrote in message
oups.com...

Hi all:

Six years ago, I built my workshop about 150ft from the house with
a 100A service. I ran a four-conductor cable to the subpanel in
the shop, and kept the ground and neutral conductors isolated from
each other. I did not bond the sub-panel ground to its own ground
rod, thinking it might cause a ground loop and/or noise in the
intercom circuit bewteen the buildings. More recently, when I put
in a spa with it's own GFCI breaker, I had several people advise me
to drive a separate ground rod for it, and that I should have done
the same for my workshop. So far, I have had no issues, but I want
to make sure I did the right thing.

My searches here have yielded many debates on the need to keep the
ground and neutral bonded only in the main panel and not the subs
(which is how I did it), but nothing about the ground rod question.
Does a remote subpanel need its own ground rod or not? Thanks in
advance, John.


Supplemental grounding gets tricky pretty fast. Excellent choice for
the 4 wire service to the garage. Now if you drive a ground rod at
the garage then the grounding conductor back to the service must be
of the same size as your service ground. If not you COULD have a
problem with an fault.... note could..

If he ran a 100A feeder to the garage panel, the grounding wire is at
least 6 gauge, and maybe 4. IIRC, #6 is the largest wire you are ever
required to use to connect a ground rod to the grounding electrode system.


thought 6 was small, so went looking. 2002nec table 250.66 for copper
3/0 is the largest, and for aluminum 250 kcmils. They are a little
bigger than 6awg.

I would probably drive a ground rod at the garage. I don't know if it
is required or not (but I think it is.) Since there's a seperate
grounding wire already, I don't think it's all that important.

Good point, it doesn't seem to be anything against driving another
grounding rod, but then, if he wired it correctly, nothing seems to
indicate he needs to.


Bob


imho,

tom @ www.WorkAtHomePlans.com

wrote:
On Wed, 12 Jan 2005 19:46:39 -0600, zxcvbob

If he ran a 100A feeder to the garage panel, the grounding wire is at
least 6 gauge, and maybe 4. IIRC, #6 is the largest wire you are ever
required to use to connect a ground rod to the grounding electrode system.


thought 6 was small, so went looking. 2002nec table 250.66 for copper
3/0 is the largest, and for aluminum 250 kcmils. They are a little
bigger than 6awg.

(I wish I could find my code book, even though it's 10 years old.) I
don't think NEC ever requires a conductor that big to connect a ground
rod to the electrode grounding system. In fact, I think there is a
specific exception that says it never has to be larger than #6 copper or
#6 copper-clad aluminum. It probably does require an equipment
grounding conductor (ground wire), or grounded conductor (neutral wire)
that big for 200A or larger feeder circuits, but that's not what we are
talking about.


I would probably drive a ground rod at the garage. I don't know if it
is required or not (but I think it is.) Since there's a seperate
grounding wire already, I don't think it's all that important.


Good point, it doesn't seem to be anything against driving another
grounding rod, but then, if he wired it correctly, nothing seems to
indicate he needs to.


Bob

Since you ran a grounding conductor with the feed to the subpanel, you do
not need to install a ground rod at that location.


Simply not true. Anything beyond a single branch circuit to a remote building
requires a ground electrode system. The only thing a 3 wire vs 4 wire feeder
affects is regrounding the neutral at the remote building.
http://members.aol.com./gfretwell/su...g2subpanel.htm

don't think NEC ever requires a conductor that big to connect a ground
rod to the electrode grounding system

Right on Bob
The GEC to a "made electrode" (rod or plate) does never have to be bigger than
#6 copper

Greg, I think you misinterpreted the pictures as indicating a ground rod for
each panel. The grounding symbol is used to only illustrate a common
ground. Read the text and you will see that an additional grounding
electrode is not required if a grounding electrode conductor was run with
the service feeder.

The original poster did the job correctly by running four wires and keeping
his grounding conductor separate from his grounded conductor (Neutral).


"Greg" wrote in message
...
Since you ran a grounding conductor with the feed to the subpanel, you do
not need to install a ground rod at that location.


Simply not true. Anything beyond a single branch circuit to a remote
building
requires a ground electrode system. The only thing a 3 wire vs 4 wire
feeder
affects is regrounding the neutral at the remote building.
http://members.aol.com./gfretwell/su...g2subpanel.htm

John Grabowski wrote:

"the_tool_man" wrote in message
oups.com...

Hi all:

Six years ago, I built my workshop about 150ft from the house with a
100A service. I ran a four-conductor cable to the subpanel in the
shop, and kept the ground and neutral conductors isolated from each
other. I did not bond the sub-panel ground to its own ground rod,
thinking it might cause a ground loop and/or noise in the intercom
circuit bewteen the buildings. More recently, when I put in a spa with
it's own GFCI breaker, I had several people advise me to drive a
separate ground rod for it, and that I should have done the same for my
workshop. So far, I have had no issues, but I want to make sure I did
the right thing.

My searches here have yielded many debates on the need to keep the
ground and neutral bonded only in the main panel and not the subs
(which is how I did it), but nothing about the ground rod question.
Does a remote subpanel need its own ground rod or not?
Thanks in advance,
John.

Since you ran a grounding conductor with the feed to the subpanel, you do
not need to install a ground rod at that location.

If you feel the need to install a ground rod it should be at the main panel.
What is your current main ground?


John Grabowski
http://www.mrelectrician.tv

Sorry John but that is bad information.

Every building that has more than a branch circuit to supply it has to
have a grounding electrode system. That can be as little as a single
ground rod if it has an impedance to ground of twenty five ohms or less.
If the impedance of the single rod is higher you have to add a second
rod. Most electricians do not bother to measure it and just add a
second rod. If the building already has an electrode such as a concrete
encased electrode then you only have to bond the service equipment
enclosure to it and your done. In all cases each separate building gets
a grounding electrode system. There are no exceptions under the US NEC.
The objective is to "limit the voltage imposed by lightning, line
surges, or unintentional contact with higher-voltage lines" and
"stabilize the voltage to earth during normal operation."

250.50 Grounding Electrode System.
If available on the premises at each building or structure served, each
item in 250.52(A)(1) through (A)(6) shall be bonded together to form the
grounding electrode system. Where none of these electrodes are
available, one or more of the electrodes specified in 250.52(A)(4)
through (A)(7) shall be installed and used. Copyright 2002 National
Fire Protection Association.

In short every building
1) needs a grounding electrode system if it is supplied with more than a
branch circuit.
2)The building disconnecting means gets bonded to the grounding
electrode system.
--
Tom H

the_tool_man wrote:
Hi all:

Six years ago, I built my workshop about 150ft from the house with a
100A service. I ran a four-conductor cable to the subpanel in the
shop, and kept the ground and neutral conductors isolated from each
other. I did not bond the sub-panel ground to its own ground rod,
thinking it might cause a ground loop and/or noise in the intercom
circuit bewteen the buildings. More recently, when I put in a spa with
it's own GFCI breaker, I had several people advise me to drive a
separate ground rod for it, and that I should have done the same for my
workshop. So far, I have had no issues, but I want to make sure I did
the right thing.

My searches here have yielded many debates on the need to keep the
ground and neutral bonded only in the main panel and not the subs
(which is how I did it), but nothing about the ground rod question.
Does a remote subpanel need its own ground rod or not?
Thanks in advance,
John.


John
The debates on this topic are endless and I won't try to settle them.
I will say that the US NEC requires that every building that has an
electrical supply that is more than a branch circuit must have a
grounding electrode system. There are no exceptions.

What you have done so far is great. Since you have an intercom between
the two buildings the code requires you to run an Equipment Grounding
Conductor (EGC) with the feeder conductors which you did. All that is
left to do is to connect the building disconnecting means to any
grounding electrodes at the garage / shop building or in the absence of
existing electrode you must install an electrode system. The point of
termination of the Grounding Electrode Conductor (GEC) to the
disconnecting means enclosure is usually done on the buss bar within the
enclosure that is bonded to the enclosure. In a three wire feeder the
bonded buss bar is the neutral buss. In a four wire feeder the bonded
buss bar is the EGC buss.

So Locate the existing electrodes or install one or more new ones and
connect them to the disconnecting means using an appropriately sized GEC.
--
Tom H

Tom, I agree that each building needs to be connected to the grounding
electrode system. However my interpretation is that the grounding electrode
system originates at the main service entrance and can be extended to
secondary buildings along with the power. Therefore a ground rod at each
secondary building is not necessary as long as the building components
(Metal piping, steel, subpanel, etc.) are bonded to the grounding electrode
system that originates from the main service.

I seem to recall an article from a few years ago in one of the trade
magazines that discussed this issue of multiple grounding along a
distribution system. I think one of the problems is that it is possible
that the ground rod in a secondary building could have less resistance than
the primary ground rod (Or water pipe). Since electricity follows the path
of least resistance it is possible that the loss of a neutral could have
current travel away from the main service to a secondary building's ground
rod. Anyway, my memory isn't that great. I could be mistaken.

John G.


"HorneTD" wrote in message
ink.net...
John Grabowski wrote:

"the_tool_man" wrote in message
oups.com...

Hi all:

Six years ago, I built my workshop about 150ft from the house with a
100A service. I ran a four-conductor cable to the subpanel in the
shop, and kept the ground and neutral conductors isolated from each
other. I did not bond the sub-panel ground to its own ground rod,
thinking it might cause a ground loop and/or noise in the intercom
circuit bewteen the buildings. More recently, when I put in a spa with
it's own GFCI breaker, I had several people advise me to drive a
separate ground rod for it, and that I should have done the same for my
workshop. So far, I have had no issues, but I want to make sure I did
the right thing.

My searches here have yielded many debates on the need to keep the
ground and neutral bonded only in the main panel and not the subs
(which is how I did it), but nothing about the ground rod question.
Does a remote subpanel need its own ground rod or not?
Thanks in advance,
John.

Since you ran a grounding conductor with the feed to the subpanel, you
do
not need to install a ground rod at that location.

If you feel the need to install a ground rod it should be at the main
panel.
What is your current main ground?


John Grabowski
http://www.mrelectrician.tv

Sorry John but that is bad information.

Every building that has more than a branch circuit to supply it has to
have a grounding electrode system. That can be as little as a single
ground rod if it has an impedance to ground of twenty five ohms or less.
If the impedance of the single rod is higher you have to add a second
rod. Most electricians do not bother to measure it and just add a
second rod. If the building already has an electrode such as a concrete
encased electrode then you only have to bond the service equipment
enclosure to it and your done. In all cases each separate building gets
a grounding electrode system. There are no exceptions under the US NEC.
The objective is to "limit the voltage imposed by lightning, line
surges, or unintentional contact with higher-voltage lines" and
"stabilize the voltage to earth during normal operation."

250.50 Grounding Electrode System.
If available on the premises at each building or structure served, each
item in 250.52(A)(1) through (A)(6) shall be bonded together to form the
grounding electrode system. Where none of these electrodes are
available, one or more of the electrodes specified in 250.52(A)(4)
through (A)(7) shall be installed and used. Copyright 2002 National
Fire Protection Association.

In short every building
1) needs a grounding electrode system if it is supplied with more than a
branch circuit.
2)The building disconnecting means gets bonded to the grounding
electrode system.
--
Tom H

On Thu, 13 Jan 2005 16:19:57 GMT, HorneTD
wrote:

the_tool_man wrote:
Hi all:

Six years ago, I built my workshop about 150ft from the house with a
100A service. I ran a four-conductor cable to the subpanel in the
shop, and kept the ground and neutral conductors isolated from each
other. I did not bond the sub-panel ground to its own ground rod,
thinking it might cause a ground loop and/or noise in the intercom
circuit bewteen the buildings. More recently, when I put in a spa with
it's own GFCI breaker, I had several people advise me to drive a
separate ground rod for it, and that I should have done the same for my
workshop. So far, I have had no issues, but I want to make sure I did
the right thing.

My searches here have yielded many debates on the need to keep the
ground and neutral bonded only in the main panel and not the subs
(which is how I did it), but nothing about the ground rod question.
Does a remote subpanel need its own ground rod or not?
Thanks in advance,
John.


John
The debates on this topic are endless and I won't try to settle them.
I will say that the US NEC requires that every building that has an
electrical supply that is more than a branch circuit must have a
grounding electrode system. There are no exceptions.

What you have done so far is great. Since you have an intercom between
the two buildings the code requires you to run an Equipment Grounding
Conductor (EGC) with the feeder conductors which you did. All that is
left to do is to connect the building disconnecting means to any
grounding electrodes at the garage / shop building or in the absence of
existing electrode you must install an electrode system. The point of
termination of the Grounding Electrode Conductor (GEC) to the
disconnecting means enclosure is usually done on the buss bar within the
enclosure that is bonded to the enclosure. In a three wire feeder the
bonded buss bar is the neutral buss. In a four wire feeder the bonded
buss bar is the EGC buss.

So Locate the existing electrodes or install one or more new ones and
connect them to the disconnecting means using an appropriately sized GEC.

This subject gets hashed around among inspectors quite a lot. It
breaks down to the definition of a branch circuit. The NEC Handbook
shows an illustration and a statement that a sub-panel requires an
electrode connected to the ground from the main panel. You'll never
be wrong to install the ground provided it is connected to the ground
from the main. An individual inspector may interpret in different
ways so sometimes it is easier to install it and be sure.

Dan

On Fri, 14 Jan 2005 12:46:58 GMT, Dan Bolt wrote:

On Thu, 13 Jan 2005 16:19:57 GMT, HorneTD
wrote:

the_tool_man wrote:
Hi all:

Six years ago, I built my workshop about 150ft from the house with a
100A service. I ran a four-conductor cable to the subpanel in the
shop, and kept the ground and neutral conductors isolated from each
other. I did not bond the sub-panel ground to its own ground rod,
thinking it might cause a ground loop and/or noise in the intercom
circuit bewteen the buildings. More recently, when I put in a spa with
it's own GFCI breaker, I had several people advise me to drive a
separate ground rod for it, and that I should have done the same for my
workshop. So far, I have had no issues, but I want to make sure I did
the right thing.

My searches here have yielded many debates on the need to keep the
ground and neutral bonded only in the main panel and not the subs
(which is how I did it), but nothing about the ground rod question.
Does a remote subpanel need its own ground rod or not?
Thanks in advance,
John.


John
The debates on this topic are endless and I won't try to settle them.
I will say that the US NEC requires that every building that has an
electrical supply that is more than a branch circuit must have a
grounding electrode system. There are no exceptions.

What you have done so far is great. Since you have an intercom between
the two buildings the code requires you to run an Equipment Grounding
Conductor (EGC) with the feeder conductors which you did. All that is
left to do is to connect the building disconnecting means to any
grounding electrodes at the garage / shop building or in the absence of
existing electrode you must install an electrode system. The point of
termination of the Grounding Electrode Conductor (GEC) to the
disconnecting means enclosure is usually done on the buss bar within the
enclosure that is bonded to the enclosure. In a three wire feeder the
bonded buss bar is the neutral buss. In a four wire feeder the bonded
buss bar is the EGC buss.

So Locate the existing electrodes or install one or more new ones and
connect them to the disconnecting means using an appropriately sized GEC.

This subject gets hashed around among inspectors quite a lot. It
breaks down to the definition of a branch circuit. The NEC Handbook
shows an illustration and a statement that a sub-panel requires an
electrode connected to the ground from the main panel. You'll never
be wrong to install the ground provided it is connected to the ground
from the main. An individual inspector may interpret in different
ways so sometimes it is easier to install it and be sure.

Dan


Might be a can of worms, without the ground rod, you could pass. Now
that you put one in you could fail till you put a second in, since now
you might not meet the 25 ohm requirement.

Just saying, if you don't follow what is in black and wihite, and can
interpet it to be anythign, what was the reasoning behind of writing
it down in black and white. The nec chould have have been one line,
Article1: Do what you feel is the max to ensure safety. End.

later,

tom @ www.BookmarkAdmin.com

John Grabowski wrote:

"HorneTD" wrote in message
ink.net...

John Grabowski wrote:

"the_tool_man" wrote in message
egroups.com...


Hi all:

Six years ago, I built my workshop about 150ft from the house with a
100A service. I ran a four-conductor cable to the subpanel in the
shop, and kept the ground and neutral conductors isolated from each
other. I did not bond the sub-panel ground to its own ground rod,
thinking it might cause a ground loop and/or noise in the intercom
circuit bewteen the buildings. More recently, when I put in a spa with
it's own GFCI breaker, I had several people advise me to drive a
separate ground rod for it, and that I should have done the same for my
workshop. So far, I have had no issues, but I want to make sure I did
the right thing.

My searches here have yielded many debates on the need to keep the
ground and neutral bonded only in the main panel and not the subs
(which is how I did it), but nothing about the ground rod question.
Does a remote subpanel need its own ground rod or not?
Thanks in advance,
John.


Since you ran a grounding conductor with the feed to the subpanel, you

do

not need to install a ground rod at that location.

If you feel the need to install a ground rod it should be at the main

panel.

What is your current main ground?


John Grabowski
http://www.mrelectrician.tv

Sorry John but that is bad information.

Every building that has more than a branch circuit to supply it has to
have a grounding electrode system. That can be as little as a single
ground rod if it has an impedance to ground of twenty five ohms or less.
If the impedance of the single rod is higher you have to add a second
rod. Most electricians do not bother to measure it and just add a
second rod. If the building already has an electrode such as a concrete
encased electrode then you only have to bond the service equipment
enclosure to it and your done. In all cases each separate building gets
a grounding electrode system. There are no exceptions under the US NEC.
The objective is to "limit the voltage imposed by lightning, line
surges, or unintentional contact with higher-voltage lines" and
"stabilize the voltage to earth during normal operation."

250.50 Grounding Electrode System.
If available on the premises at each building or structure served, each
item in 250.52(A)(1) through (A)(6) shall be bonded together to form the
grounding electrode system. Where none of these electrodes are
available, one or more of the electrodes specified in 250.52(A)(4)
through (A)(7) shall be installed and used. Copyright 2002 National
Fire Protection Association.

In short every building
1) needs a grounding electrode system if it is supplied with more than a
branch circuit.
2)The building disconnecting means gets bonded to the grounding
electrode system.
--
Tom H
Tom, I agree that each building needs to be connected to the grounding
electrode system. However my interpretation is that the grounding electrode
system originates at the main service entrance and can be extended to
secondary buildings along with the power. Therefore a ground rod at each
secondary building is not necessary as long as the building components
(Metal piping, steel, subpanel, etc.) are bonded to the grounding electrode
system that originates from the main service.

I seem to recall an article from a few years ago in one of the trade
magazines that discussed this issue of multiple grounding along a
distribution system. I think one of the problems is that it is possible
that the ground rod in a secondary building could have less resistance than
the primary ground rod (Or water pipe). Since electricity follows the path
of least resistance it is possible that the loss of a neutral could have
current travel away from the main service to a secondary building's ground
rod. Anyway, my memory isn't that great. I could be mistaken.

John G.

John
We can talk what ifs until the cows come home. The requirement in the
US NEC is plain. If the building is supplied by a feeder rather than by
a branch circuit it must have a grounding electrode system and the
building disconnecting means must be bonded to it. It makes no
difference whether there is or is not an Equipment Grounding conductor
run with the feeder a grounding electrode system is still required at
each building. Which conductor of the feeder gets bonded to the
Grounding Electrode System at each building is dependent on whether
there is an EGC in the feeder. Either way you must bond the building
disconnecting means to a grounding electrode at the building that the
building disconnecting means serves. The US NEC does not allow any
other course of action.
--
Tom H