As the previous poster said, ask the inspector:

http://ths.gardenweb.com/forums/load/wiring/msg1115444822420.html

Not correct if the panel is in a detached structure.

If you do not have a water pipe, use two grounding rods.

You can use a single rod if it is less than 25 ohms to earth ground.
To make the measurement you need to drive another rod.
Since you are only required to add one additional rod if the original is over 25 ohms, and no one want to remove a rod, just drive two rods from the start and skip the measurement.

It's not complicated if you look for the following:

Form the cited post:

"The requirement for no other metallic connections is very important. No phone line, cable tv lines, metal water lines. NO connection.
This is to prevent the return of any currents on a secondary ground connection.
If the conenction was made, the return currents would divide based on circuit impedance and a phone line would likely be quickly destroyed."

If a structure has more than one circuit, it must have a grounding system. That means a primary ground system (two ground rods will do although there are other ways) plus you have to bond any water piping, structural metal, etc...
This is the way it has been for decades.

Prior to 2008, the no metallic connection exception allows you to avoid running a grounding conductor between the buildings. That exemption NO LONGER EXISTS and it was never a particularly good idea to begin with.

You are confusing bonding of neutral (groundED conductor) and earth grounding of the panel.

As a sub-panel the neutral is not bonded to earth ground in the separate building.
As a separate building grounding electrodes are required.

Any metal water pipe must be bonded to the breaker box ground so that a wire fault to any pipe causes a circuit breaker to trip. Connecting to water pipes is bonding for human safety. And is earthing that is insufficient.

This is only about what electrode is sufficient. Whether that sub-panel must be earthed is another and different topic.

Thanks. I was misreading the question. That's the problem with me and the small phone screens. I apologize.

Thanks for all the responses. In my case, and given that I'm a total newbie at this, I think "ask the inspector" was probably the best advice.

But just to clear up my situation: I have a detached garage. Currently (no pun intended) I have a single 110V circuit running out to it from the house via an underground conduit that powers a couple of lights and receptacles.

However, I'm planning to move my woodworking shop out there and two of my machines run off of 220V. Since the basement is finished now, reworking the circuit that runs from the house to the garage would be very difficult and disruptive.

But it would be relatively easy to bring entirely new, separate service in from the overhead street wires that run right in front of garage, and that's what I'm planning to do. So it wouldn't be a sub panel... it would be a brand new main panel with its own meter.

I'm just wondering though... would it be possible to use the existing underground conduit in lieu of a water pipe? My only concern is that the panel would probably have to be mounted in the corner diagonally opposite where the conduit comes into the garage. So a ground from that panel would have to run around 30' of walls to get to the conduit.

I'm going to ask the local Building Dept. anyway, but feel free to comment.

No offense, but you are supposed to know what you are doing BEFORE you do a job.
An inspector is NOT there to tell you what to do. He/she is there to (hopefully) catch the mistakes you might make.
Also, it's absolutely NOT up to what he or she "wants". It is up to them to interpret and enforce the codes in place in your area.

And any AHj should tell you to learn how to do re job.

They are not here to give advice, and that is what you are asking.
They do answer code questions that are asked many times, but rarely are wiling to lay out how to do a job.

"would it be possible to use the existing underground conduit in lieu of a water pipe? My only concern is that the panel would probably have to be mounted in the corner diagonally opposite where the conduit comes into the garage. So a ground from that panel would have to run around 30' of walls to get to the conduit."

The long distance is not a good idea, and will decrease the performance of the grounding electrode system. It will also be sort of pricey given the size of the grounding electrode conductor required (and that depends on te service ampacity).

Listed electrodes are not all that expensive, and you would likely meet some resistance from the AHJ trying to re-purpose a section of conduit as a grounding electrode, if they would allow it at all.
At the very least they would be well within their rights to want it exposed for examination.

Just count on driving two rods at least 6 feet apart.
Services are not a really good idea for a beginner.

There are many details (including dealing with the local POCO) that all must be done correctly.
Some of the rules you need to follow are not even in the NEC, since it technically does not apply to the distribution line from the POCO.
The NEC has some rules for overhead lines, clearances, masts, etc. but the POCO still has the final say, not even the AHJ.

How about you get your facts in order and arm yourself with knowledge against uninformed inspectors.

They ONLY have the last word on things IF they are correct in their code interpretations. They CANNOT just make shi* up.

And job insecurity when something goes wrong and you can no longer get insurance.

The NEC called for a single grounding electrode for many years, and it could even be a metal water line with 10 feet i in earth contact.

This was changed after it was simply found inadequate in some soil condition.

A rod was than added along with the water line is usable.

If no water line is available you must show the rod is 25 ohms or less to earth.
Making this measurement requires a second rod to measure against.
No one want to bother removing the second rod, and even if the first rod is more than 25 ohms, only one additional rod is required.
In most cases it is just not worth the hassle, so two rods are driven.
The NEC also requires the bonding of all electrodes, even from other systems (phone, cable TV, TV & radio antennas, etc.) to form a single grounding electrode system.

There is not any great risk in this.

In the USA we have way over 50 authorities, all using whatever code they have adopted (often the NEC as a basis, but with local alterations).

The federal labor department has no say over things like state and local licensing, and licenses are issued with all sorts of limits (one city, one county, one state) but there are NO nationwide licenses.

The USA is a republic, made up of 50 sovereign states.

We hold individuals responsible for their actions, and saying 'the inspector made me do it' is not going to hold up well in a civil action (though it may protect you from criminal action).

Once you lose a major civil action you will find your errors and omissions insurance painfully expensive (and in many places it is required to be in business).

Probbaly time to find another profession.

The reason I brought it up is because it does not good for brick to argue NEC procedures to the Canadians nor you to argue CEC rules to those south of the border.

Since the original questioner was from the US, I would recommend he followed us who gave the correct, legal, and safe rules that apply in the US.

Just keep your socialist utopia on your side of the border.

There is no reason to even try to "catch up" with such a scheme.