If I am wiring a 100 amp subpanel in my detached garage with 240 using
2-2-2-4 AL, I am carrying the ground from my house's main panel (60 amp
breaker). Does NEC require that I have a grounding rod at my detached
garage? If that is the case, should I only be running 2-2-2AL?
thanks. Any arguments for using copper? The AL seems like it may be
overrated, but cheaper in the end.

According to :
If I am wiring a 100 amp subpanel in my detached garage with 240 using
2-2-2-4 AL, I am carrying the ground from my house's main panel (60 amp
breaker). Does NEC require that I have a grounding rod at my detached
garage? If that is the case, should I only be running 2-2-2AL?

It is a trifle confusing. In our codes, not all outbuildings need their
own grounding system. But if it does, the feed should only be 3-wire,
not four. This is probably something you need to ask your local
code authority/inspectors.

#2 is a bit of overkill for 60A. Why aren't you breakering it for 100A
at the main?

thanks. Any arguments for using copper? The AL seems like it may be
overrated, but cheaper in the end.

Yeah, you seem to be a bit large for the AL. My 100A subfeed to
the garage (buried) is #3 (I think) Al. In copper, it'd be #4.
The Al was about a third of the price of it in copper. With 60A,
you could probably go a size smaller.

While copper is vastly perferred for ordinary circuits, for high amperage
subpanel feeds Al is perfectly fine (if the proper attention is paid
to connectors, anti-oxidant grease etc).
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

wrote in message
oups.com...
If I am wiring a 100 amp subpanel in my detached garage with 240 using
2-2-2-4 AL, I am carrying the ground from my house's main panel (60 amp
breaker). Does NEC require that I have a grounding rod at my detached
garage? If that is the case, should I only be running 2-2-2AL?
thanks. Any arguments for using copper? The AL seems like it may be
overrated, but cheaper in the end.


Grounding is done at the electrical service. Any installed panel after the
service (meter location) is considered a sub panel. Sub panels must have
seperate hots neutral and ground conductors. Using the earth as return path
can be dangerous. ( ya I know lots of places do it and are installing it as
I type, still wrong).

A supplemental ground rod at the garage is confusing and complicated. I
encourage you to go to the library and find the "Soars book on Grounding"
Simplified explanations for a complex subject. Lots of good pictures and
illustrations.

2-2-2-4 is correct, better check your 60 amp breaker, I will bet you have
trouble landing #2.


As long as you understand AL and work to its needs there is nothing wrong
with the wire. Every problem I have seen in 20 plus years of electrical work
with AL can be attributed to the workmanship. Utilities seldom use copper
any more. Cost and weight is their issues.

Some jurisdictions require grounding at remote buildings. Best check
anonymously before you go to far astray.

wrote in message
oups.com...
If I am wiring a 100 amp subpanel in my detached garage with 240 using
2-2-2-4 AL, I am carrying the ground from my house's main panel (60 amp
breaker). Does NEC require that I have a grounding rod at my detached
garage? If that is the case, should I only be running 2-2-2AL?
thanks. Any arguments for using copper? The AL seems like it may be
overrated, but cheaper in the end.


Read article 250.32(A). Run the four conductors from your main service.
Install a ground rod or two for your detached garage. Install a grounding
terminal bar in the garage subpanel to connect the #4 aluminum from your
main feed and the grounding electrode conductor (#6 or #4 copper) from your
ground rods together. All grounding conductors for your branch circuits
should also terminate on this bar. Keep the neutral conductor isolated from
the grounding conductors. The #2 aluminum is good for 75 or 90 amps
depending on your terminal ratings. Have your work inspected.

It is okay to use aluminum, but I don't recommend its usage underground and
especially for direct burial. Moisture and aluminum don't go well together.


John Grabowski
http://www.mrelectrician.tv

If you don't run the ground with the feed conductors, you have to meet
certain conditions like nothing conductive and grounded can be installed
between the two buildings. At least where direct burial cable is concerned,
you get one little nick in it and it disintegrates



"Chris Lewis" wrote in message
...
According to John Grabowski :

wrote in message
oups.com...
If I am wiring a 100 amp subpanel in my detached garage with 240 using
2-2-2-4 AL, I am carrying the ground from my house's main panel (60 amp
breaker). Does NEC require that I have a grounding rod at my detached
garage? If that is the case, should I only be running 2-2-2AL?
thanks. Any arguments for using copper? The AL seems like it may be
overrated, but cheaper in the end.

Read article 250.32(A). Run the four conductors from your main service.
Install a ground rod or two for your detached garage. Install a
grounding
terminal bar in the garage subpanel to connect the #4 aluminum from your
main feed and the grounding electrode conductor (#6 or #4 copper) from
your
ground rods together. All grounding conductors for your branch circuits
should also terminate on this bar. Keep the neutral conductor isolated
from
the grounding conductors. The #2 aluminum is good for 75 or 90 amps
depending on your terminal ratings. Have your work inspected.

Are you _sure_ about the four wire with ground interconnected to a new
ground rod
in the outbuilding?

As I understand it, it's either 3 wire plus new ground electrode, or 4
wire with
no new ground electrode. In both cases with the ground/neutral lug
_removed_
in the subpanel. Not a mixture of both. Ground loops.

It is okay to use aluminum, but I don't recommend its usage underground
and
especially for direct burial. Moisture and aluminum don't go well
together.

Copper and moisture don't go well together in the presence of electricity
_either_. Appropriately rated underground Al cable will be no worse than
the
equivalent Cu. The difference is in the care needed with terminations,
not
the cable itself.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

Chris Lewis wrote:

According to John Grabowski :

wrote in message
groups.com...

If I am wiring a 100 amp subpanel in my detached garage with 240 using
2-2-2-4 AL, I am carrying the ground from my house's main panel (60 amp
breaker). Does NEC require that I have a grounding rod at my detached
garage? If that is the case, should I only be running 2-2-2AL?
thanks. Any arguments for using copper? The AL seems like it may be
overrated, but cheaper in the end.


Read article 250.32(A). Run the four conductors from your main service.
Install a ground rod or two for your detached garage. Install a grounding
terminal bar in the garage subpanel to connect the #4 aluminum from your
main feed and the grounding electrode conductor (#6 or #4 copper) from your
ground rods together. All grounding conductors for your branch circuits
should also terminate on this bar. Keep the neutral conductor isolated from
the grounding conductors. The #2 aluminum is good for 75 or 90 amps
depending on your terminal ratings. Have your work inspected.


Are you _sure_ about the four wire with ground interconnected to a new ground rod
in the outbuilding?

As I understand it, it's either 3 wire plus new ground electrode, or 4 wire with
no new ground electrode. In both cases with the ground/neutral lug _removed_
in the subpanel. Not a mixture of both. Ground loops.

If you run 3 wires (assuming 2 hot wires and a grounded neutral) you
most definitely do leave the bonding lug (screw) in the panel -- the
panel is a "service entrance".

If you run a separate ground wire to an outbuilding, the rules get kind
of fuzzy. You would remove the bonding lug (screw) from the panel, and
it's now a subpanel rather than a service entrance, but I think a
supplemental grounding electrode would still be a *good* thing.

Note that if the buildings are interconnected by a common water or gas
pipes, telephone lines, CATV, etc, you are *required* to run a separate
ground wire.

Bob

According to RBM rbm2(remove :
If you don't run the ground with the feed conductors, you have to meet
certain conditions like nothing conductive and grounded can be installed
between the two buildings. At least where direct burial cable is concerned,
you get one little nick in it and it disintegrates

Which is what John was proposing - ground conductor with feed (4 wire) and
grounding electrodes at _both_ ends. Ground loop. The electrodes themselves
will disintegrate.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

According to zxcvbob :

As I understand it, it's either 3 wire plus new ground electrode, or 4 wire with
no new ground electrode. In both cases with the ground/neutral lug _removed_
in the subpanel. Not a mixture of both. Ground loops.

If you run 3 wires (assuming 2 hot wires and a grounded neutral) you
most definitely do leave the bonding lug (screw) in the panel -- the
panel is a "service entrance".

We're talking subpanels (downstreams from main panels) here exclusively, not
separate service entrances.

If you leave the bonding lug in the panel, the subpanel's grounding goes through
the subpanel feed's neutral. Distinctly bad. Lose that neutral and all hell
breaks loose.

Subpanels always have their bonding lugs out. Either they get their grounding
from the fourth wire in the feed, or they get their grounding from grounding
electrode[s]. In neither case is it connected to the neutral.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

Chris Lewis wrote:

According to zxcvbob :


As I understand it, it's either 3 wire plus new ground electrode, or 4 wire with
no new ground electrode. In both cases with the ground/neutral lug _removed_
in the subpanel. Not a mixture of both. Ground loops.



If you run 3 wires (assuming 2 hot wires and a grounded neutral) you
most definitely do leave the bonding lug (screw) in the panel -- the
panel is a "service entrance".


We're talking subpanels (downstreams from main panels) here exclusively, not
separate service entrances.

If you leave the bonding lug in the panel, the subpanel's grounding goes through
the subpanel feed's neutral. Distinctly bad. Lose that neutral and all hell
breaks loose.

Subpanels always have their bonding lugs out. Either they get their grounding
from the fourth wire in the feed, or they get their grounding from grounding
electrode[s]. In neither case is it connected to the neutral.


From the main panel's perspective, we are talking about a subpanel.

But from the outbuilding's perspective, the box is a service entrance
and must be listed as such if it is fed without a separate grounding
conductor (which is what I think you were proposing.)

Maybe the rules are different up there in Canada, but I installed a
3-wire 240/120V feeder to an outbuilding 1.5 year ago and had it
inspected. The incoming grounded neutral wire is bonded to the panel,
and I had to add a grounding electrode.

Bob

I did one just two months ago in NY. A detached garage with an existing
three wire feed in pvc to the house. I had to run two ground rods and did
have to bond the neutral. Like Bob said, I was given specific instructions
about not having any other conductive, grounded paths. i.e.. telephone,
catv, gas, water



"zxcvbob" wrote in message
...
Chris Lewis wrote:

According to zxcvbob :


As I understand it, it's either 3 wire plus new ground electrode, or 4
wire with
no new ground electrode. In both cases with the ground/neutral lug
_removed_
in the subpanel. Not a mixture of both. Ground loops.


If you run 3 wires (assuming 2 hot wires and a grounded neutral) you most
definitely do leave the bonding lug (screw) in the panel -- the panel is
a "service entrance".


We're talking subpanels (downstreams from main panels) here exclusively,
not
separate service entrances.

If you leave the bonding lug in the panel, the subpanel's grounding goes
through
the subpanel feed's neutral. Distinctly bad. Lose that neutral and all
hell
breaks loose.

Subpanels always have their bonding lugs out. Either they get their
grounding
from the fourth wire in the feed, or they get their grounding from
grounding
electrode[s]. In neither case is it connected to the neutral.


From the main panel's perspective, we are talking about a subpanel.

But from the outbuilding's perspective, the box is a service entrance and
must be listed as such if it is fed without a separate grounding conductor
(which is what I think you were proposing.)

Maybe the rules are different up there in Canada, but I installed a 3-wire
240/120V feeder to an outbuilding 1.5 year ago and had it inspected. The
incoming grounded neutral wire is bonded to the panel, and I had to add a
grounding electrode.

Bob

On Wed, 26 Oct 2005 16:08:13 -0400, "John Grabowski"
wrote:


wrote in message
roups.com...
If I am wiring a 100 amp subpanel in my detached garage with 240 using
2-2-2-4 AL, I am carrying the ground from my house's main panel (60 amp
breaker). Does NEC require that I have a grounding rod at my detached
garage? If that is the case, should I only be running 2-2-2AL?
thanks. Any arguments for using copper? The AL seems like it may be
overrated, but cheaper in the end.


Read article 250.32(A). Run the four conductors from your main service.
Install a ground rod or two for your detached garage. Install a grounding
terminal bar in the garage subpanel to connect the #4 aluminum from your
main feed and the grounding electrode conductor (#6 or #4 copper) from your
ground rods together. All grounding conductors for your branch circuits
should also terminate on this bar. Keep the neutral conductor isolated from
the grounding conductors. The #2 aluminum is good for 75 or 90 amps
depending on your terminal ratings. Have your work inspected.

It is okay to use aluminum, but I don't recommend its usage underground and
especially for direct burial. Moisture and aluminum don't go well together.


John Grabowski
http://www.mrelectrician.tv
Mr. Grabowski gave you the correct information.

Dan

"Chris Lewis" wrote in message
...
According to John Grabowski :

wrote in message
oups.com...
If I am wiring a 100 amp subpanel in my detached garage with 240
using
2-2-2-4 AL, I am carrying the ground from my house's main panel
(60 amp
breaker). Does NEC require that I have a grounding rod at my
detached
garage? If that is the case, should I only be running 2-2-2AL?
thanks. Any arguments for using copper? The AL seems like it
may be
overrated, but cheaper in the end.

Read article 250.32(A). Run the four conductors from your main
service.
Install a ground rod or two for your detached garage. Install a
grounding
terminal bar in the garage subpanel to connect the #4 aluminum
from your
main feed and the grounding electrode conductor (#6 or #4 copper)
from your
ground rods together. All grounding conductors for your branch
circuits
should also terminate on this bar. Keep the neutral conductor
isolated from
the grounding conductors. The #2 aluminum is good for 75 or 90
amps
depending on your terminal ratings. Have your work inspected.

Are you _sure_ about the four wire with ground interconnected to a
new ground rod
in the outbuilding?

As I understand it, it's either 3 wire plus new ground electrode, or
4 wire with
no new ground electrode. In both cases with the ground/neutral lug
_removed_
in the subpanel. Not a mixture of both. Ground loops.


From 1999 NEC:

250-32.Two or more Buildings or Structures Supplied from a Common
Service.

(a) Grounding Electrode. Where two or more buildings or structures are
supplied from a common ac service by a feeder(s) or branch
circuit(s), the grounding electrode(s) required in Part C of this
article at each building or structure shall be connected in the manner
specified in (b) or (c). Where there are no existing grounding
electrodes, the grounding electrode(s) required in Part C of this
article shall be installed.

Exception. A grounding electrode at separate buildings or structures
shall not be required where only one branch circuit supplies the
building or structure and the branch circuit includes an equipment
grounding conductor for grounding the noncurrent-carrying parts of all
equipment.

(b) Grounded Systems. For a grounded system at the separate building
or structure, the connection to the grounding electrode and grounding
or bonding of equipment, structures, or frames required to be grounded
or bonded shall comply with either (1) or (2).

(1) Equipment Grounding Conductor. An equipment grounding conductor as
described in Section 250-118 shall be run with the supply conductors
and connected to the building or structure disconnecting means and to
the grounding electrode(s). The equipment grounding conductor shall be
used for grounding or bonding of equipment, structures, or frames
required to be grounded or bonded. Any installed grounded conductor
shall not be connected to the equipment grounding conductor or to the
grounding electrode(s).

(2) Grounded conductor. Where (1) an equipment grounding conductor is
not run with the supply to the building or structure, and (2) there
are no continuous metallic paths bonded to the grounding systems in
both buildings or structures involved, and (3) ground-fault protection
of equipment has not been installed on the common ac service, the
grounded circuit conductor run with the supply to the building or
structure shall be connected to the building or structure
disconnecting means and to the grounding electrode(s) and shall be
used for grounding or bonding of equipment, structures, or frames
required to be grounded or bonded.

Part C, Section 250-50 covers the connection of metal underground
pipe, metal frame of the building, concrete encased electrodes, and
ground rings to form the grounding electrode system. Interior metal
water pipe located more than 5 feet from the point of entrance to the
building shall not be used as part of the grounding electrode system.
A metal underground pipe shall be supplemented by an additional
electrode.

Section 250-52. Made and Other Electrodes. Where none of the
electrodes specified in Section 250-50 is available, one or more of
the electrodes specified in (b) through (d) shall be used.

(b) other local metal underground systems or structures
(c) rod a pipe electrodes
(d) plate electrodes

My reading of 2005NEC 250.32 is:

If only a single branch ckt (or multiwire branch ckt) is run to the
building, and the circuit includes a ground wire, a ground rod is not
required at the building. In all other cases (including the feeder
described) ground rod(s) or other grounding electrode is required at the
building.

There are then 2 options :
1. A grounding conductor IS run to the building: the grounding conductor
is connected to a ground bar and ground rod. The neutral bar is not
connected to the panel ground. There is a parallel path with (neutral)
and (ground electrodes at both ends with earth) but the earth path will
have a significantly higher resistance.

2. A grounding conductor IS NOT run to the building: the neutral is
connected (through a main bonding jumper) to the ground system and
ground rod. This is like a service. There can be no other continuous
metal paths that are bonded the ground conductor at both ends, and the
feeder shall not be fed with a GFCI (which would cause an immediate trip).

(I have seen electricians argue over this section.)

bud--


wrote:

If I am wiring a 100 amp subpanel in my detached garage with 240 using
2-2-2-4 AL, I am carrying the ground from my house's main panel (60 amp
breaker). Does NEC require that I have a grounding rod at my detached
garage? If that is the case, should I only be running 2-2-2AL?
thanks. Any arguments for using copper? The AL seems like it may be
overrated, but cheaper in the end.

On Thu, 27 Oct 2005 11:35:05 -0500, Bud--
wrote:

My reading of 2005NEC 250.32 is:

If only a single branch ckt (or multiwire branch ckt) is run to the
building, and the circuit includes a ground wire, a ground rod is not
required at the building. In all other cases (including the feeder
described) ground rod(s) or other grounding electrode is required at the
building.



Can't you also just run 240V through two conductors, and drive an
isolation transformer with it's own local ground?

According to Chris Lewis :
According to zxcvbob :

But from the outbuilding's perspective, the box is a service entrance
and must be listed as such if it is fed without a separate grounding
conductor (which is what I think you were proposing.)

Maybe the rules are different up there in Canada, but I installed a
3-wire 240/120V feeder to an outbuilding 1.5 year ago and had it
inspected. The incoming grounded neutral wire is bonded to the panel,
and I had to add a grounding electrode.

Think logically about it for a moment - pull full amps on one side
of the subpanel. You'll pull the neutral 3V or so way from ground
potential. Yet, you have a grounding electrode at either end of it.
Means current flow between grounding electrode - in some cases
several amps in normal operation. Corrosion of grounding electrodes.

Worse, sever the subpanel neutral. Now the neutral return from the
whole subpanel is trying to go through the grounding electrodes, and
depending on electrode-to-dirt resistances, every grounded device
connected to the subpanel could present frame voltages relative to
ground as much as 120V.

Then I realized, if you _don't_ bond the grounding electrode to the neutral
in the outbuilding with a three wire feed, a hot ground short in the outbuilding
has to push the fault current thru the dirt. Which in most cases would NOT trip
a breaker.

Which is probably the worse of the above evils.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.