Replies

1. 
   DougB | Dec 24, 2004 07:59pm | #1

   I recently built my dream detached garage (more workshop than garage) and did not ground separately.   It is connected to the house main panel and that is grounded.  One thing I did, however, was invest in shop safety as I have 2 young children.  I have a 100 amp feed coming into the garage.  On the first panel I have only 4 breakers, three of which control the lights, door opener, and several single outlets.  Among other things, these outlets provide power to my heater, radio, battery charger, etc..  One breaker is another 100 amp that feeds a separate, and larger panel.  This panel has about a dozen breakers feeding power to stationary tools as well as outlets portable tools are plugged into.  When not in the shop I only need to turn off one breaker and every tool in my shop is immobilized.  My additional investment only amounted to $70 but that is a small price to pay to ensure the safety of my children.

   happy wiring and Merry Christmas

   doug

1. 
   Manchild | Dec 24, 2004 08:31pm | #2

   Good idea Doug. It's details like these that can make something special.

2. 
   bones | Dec 24, 2004 09:30pm | #3

   You say you have a 100 amp panel in the garage. By that, do you mean you have a 100 amp sub-panel wired off of your main service entrance? If so, the ground of the sub-panel should be bonded to the main panel. I am assuming the garage is attached to the house (not far from the main). If you pull the cover off of your main service panel, you will see two bus-bars (most-likely) running down the center (if you have a breaker-box). Each supplies 120. You should also see a neutral/ground bar.  The main box should have a large copper ground wire going from the panel out to a ground rod somewhere. The neutrals and grounds are bonded together. I don't know the code in your area, but here, you need two ground points. I have a #4 copper ground to a ground rod, and a second ground to the copper plumbing that goes into the slab and to ground.  Hope this helps.

1. 
   Manchild | Dec 25, 2004 01:25am | #5

   Thank you! I will run a #6 or larger back to the main. I'll look in my subpanel to see if there is a way to disconnect one bar to make it separate from the common.

1. 
   Manchild | Dec 25, 2004 02:46am | #6

   I just read the instructions for the sub-panel. I need to buy a separate bar for the ground.

3. 
   BarryO | Dec 24, 2004 10:49pm | #4

   David,

   since you have an attached garage, the garage panel needs to be wired as a subpanel.  There must be four wires from the main panel to the subpanel: 2 hots, 1 "neutral" (called the "grounded" conductor in the Code), and 1 equipment grounding conductor.  The "neutral" and grounding conductors are wired to seperate bus bars in the subpanel that are not bonded together.  You don't need additional ground electrodes; if you do install any additional ones anywhere, they must be connected back to the ground rods already in place with at least a #6 copper wire.

   Doug,

   since your detached garage is a separate building, and you have more than one branch circuit in it, you must install a grounding electrode system at the garage.  From the 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.

   The only exception made is if there is only one branch circuit in the garage.

   You can wire the garage panel as a subpanel, with 4 wires running back to the main.  You may be able to wire the garage panel as a main panel instead, with only 3 wires running back to the house panel:

   (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 system 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.