How many conductors do you have to run to a main breaker subpanel which is located in a garage 100 ft away. Can you get away with 2 hots and a neutral If you pound a ground rod at the subpanel. I cannot find the answer in the code book.

A subpanel must be a four wire feed.

Neutral and ground may not be bonded together at the subpanel.

A separate grounding system must be installed at the subpanel.

Do you need me to get the sections from the NEC 2008 for you?

My advice is the same as Don's, 4 wire is needed, althou, there is an exception to allow a 3 wire feeder, however, that exception is based on specific requirements that can be difficult to determine.

We basically have a standard answer here for all questions such as this, 4 wire.

The cost of one more conductor is far better than the possibility of being incorrect to allow the exception.

By the way, sounds like you have read the Code and trying to find the statement, " A subpanel in a detached building needs x- wire feeder", or something of that nature.

Stop looking, you will not find it. The Code is not a design guide, and certainly not an how to instruction book. It takes some time invested to understand the Code, and without having field knowledge is difficult to understand and apply the Code properly.

I will however take Don up on his offer, to provide the relevant Code section(s) that apply to your question. Not as a challenge, or a test, but I know that Don is and has been on a mission to learn the Code, correctly and in depth, so, then, I suppose it is a test of sorts.

Don, lets see what you have.

Four wire requirement - 250.32(B) - Equipment grounding conductor and connection requirement. How does this apply? Your feeder must have two ungrounded (hot) conductors and one grounded (neutral) conductor. Article 250.32(B) requires that an equipment grounding conductor be run from the main panelboard to the secondary panelboard. Therefore, four conductors are needed. Also, there is a requirement that says all conductors are to be in the same raceway or cable. So, you would need an SER cable from the main service panel to the second panelboard.

More than one structure 225.31
Disconnect - 225.32
Lighting - 210.70 (2)
Grounding Electrode - 250.32(A)
Equipment grounding conductor - 250.32(B)