On Friday, May 20, 2016 at 2:02:22 PM UTC-4, trader_4 wrote:
On Friday, May 20, 2016 at 12:56:53 PM UTC-4, wrote:
On Fri, 20 May 2016 10:33:02 -0400, wrote:

On Fri, 20 May 2016 13:09:00 GMT, (Scott Lurndal)
wrote:

John G writes:
I want to put a sub-panel in a connected garage. Can I use 6-ga. 3-wire to supply a panel with 4 breakers (20A each)? Do you have to consider the possible use of all of the circuits carrying the maximum load? Thanks!

You do need to consider what the total load of the panel will be at any given time. Will you be running machines constantly or intermittently? You do not have to total up the rating of the individual circuit breakers.

You need four wires for a sub-panel and I think a ground rod for lightning protection is a good idea.

Do not use a ground rod with the subpanel; aside from being a NEC
code violation, it can induce current in the grounding conductor.
There should only be one grounding point in the system, and that
should be at the service entrance.

There is no limit to the number of rods or other electrodes you use,
only a limit of one main bonding jumper where the neutral gets tied to
the grounding electrode system. In fact, if this sub panel is in a
separate structure, another electrode is required.
That was my interpretation too. Ground at avery distribution panel,
but only one ground to neutral bod (as close to the main service
entrance as possible)

You can have more than one ground, but a separate ground at every
subpanel is not required either.

....unless the sub-panels are each in different buildings.