I am a DIYer and want to do this project on my own. I do have a licensed electrician that I can fall back on, and will use at the end of the project to check it, but I'd really like to do this. I've wired my second floor, but have not done this type of project before.

From what I understand at this point, I'd like to use a 100 amp subpanel in a detached garage that is approximately 90' away (15' of which is outside) from the 200amp main panel. I believe that I need 6/3 wire with conduit at least 18" underground.

Is a 100amp breaker in the main panel sufficient? I want to run a fridge, A/C, multiple power tools, an electric range, a HE heater, along with other general household items.

I understand I'll need a grounding rod that's at least 8 feet (Garage used to have electricity, so I assume there is one somewhere, but can't find it). How do you get this driven so far into the ground?

Where does the wire (#6, I believe) from the grounding rod connect in the subpanel?

Once I have the panel set up, I'm good. I just need to get this in before winter.

Thank you for all your help.

  • Is this a detached garage?
    – Tester101
    Oct 25, 2017 at 13:48
  • Welcome to DIYSE, Joe. I removed your product recommendation request. Please see the help pages for why. In order to suggest a panel and breaker size we'd need to know something about your power needs in the garage. Please edit your question to describe that.
    – isherwood
    Oct 25, 2017 at 13:55
  • 2
    Have you tried searching the site? All your questions have probably been answered at some point (probably multiple times). Don't use the StackExchange search, it is terrible. Use Google, but include "diy.stackexchange.com" in the query.
    – Tester101
    Oct 25, 2017 at 13:57
  • 2
    @JoeLaFrance How close you are to bedrock, usually.
    – Tester101
    Oct 25, 2017 at 16:11
  • 1
    People always seem to ask this question too late, but if you put an UFER ground in the concrete slab or wall footing, you don't need a ground rod at all (and you'll have a better ground.) But that has to be planned before the slab is poured.
    – Ecnerwal
    Oct 25, 2017 at 17:29

2 Answers 2


Well, you asked several questions and if you search on this site you will find many questions and answers regarding sub-panels. We have covered this same subject many times. It may be the most asked questions from novices.

It would be a Code violation, and safety issue, to protect #6 wire with a 100 amp breaker. You will need #3 copper or #1 aluminum if you want to protect it with a 100 amp breaker. You can use whatever size panel you want at the garage but if you want to fully utilize it you should feed it with proper sized wire and protect that with a properly sized breaker.

You can drive the ground rod with a fence post driver they sell at the farm centers. If you have good soil they are easy to drive.

The #6 grounding electrode conductor connects to the ground bus and the neutral bus is kept isolated. Take the green screw (or the jumper strap) that came with your panel and throw it away.

Good luck and stay safe!

  • #3 wire. Got it. how did the grounding electrode connect to the grounding rod, with some sort of connector? I have clay, so it will not be easy, but I figured I'd ask. Oct 25, 2017 at 18:54
  • 1
    @JoeLaFrance #1 aluminum. You don't want to use copper at those large sizes, it's needlessly costly and you will have dissimilar metal corrosion since the panel lugs are aluminum. Oct 25, 2017 at 22:09
  • 1
    The #6 grounding electrode conductor usually attaches to the ground with what is called an acorn clamp. You can also use a small ground clamp. The National Electrical Code has an exception that allows you to bury the ground rod horizontally IF the soil is such that makes driving it impractical. Also if you have 1\2" re-rod or larger in the footing that is exposed you can use that for a grounding electrode in place of the ground rod.
    – ArchonOSX
    Oct 26, 2017 at 0:52
  • 1
    As Harper said if you price out copper and aluminum you will probably want to buy the aluminum. Just make sure you use anti-oxidation paste on the aluminum wire where you terminated it at the panel and breaker. And torque the terminals to the specs of the manufacturer.
    – ArchonOSX
    Oct 26, 2017 at 1:00

For driving the ground rods in:

Obtain various lengths of 3/4 inch (19 mm) pipe—galvanized and black—in various lengths from 3 inches to 5 feet (7.5 cm and 150 cm). I bought two 3/4 inch caps available to be sacrificed in the process. The pipe is not harmed.

Start with a pipe in the 3–5 foot range (for an 8 foot (2.4 m) rod). Screw on one cap and slide the pipe plus cap over the top of the rod and bang it into the ground using only the pipe. (That is, slide it up a few feet and then forcibly slide it down which causes the pipe cap to strike the top of the rod.) This is easy to do without a ladder or hammer.

Once the rod has submerged far enough, the pipe is stopped by the ground so change to a shorter pipe (like in the 2–3 foot range). Even when I switch down to a 12 inch pipe, I still get good driving progress even though the pipe's mass is distinctly light. With the rod protruding about a foot, it is then easy to use a sledge or other heavy hammer to drive it below ground level. I keep the top of the rod beautiful by protecting it with a 3 inch pipe and cap when bashing away with the hammer.

Usually two pipe caps survive long enough for installation of two ground rods, though that depends strongly on the hardness of the soil.

Here is the top end of a grounding rod (it's upside down; notice the end finish so you can't cut it off without it being obvious): enter image description here

Here is a cable clamp for the grounding rod: enter image description here

Here is how it looks installed: enter image description here

  • So it does not have to be one be continuous rod? How are the pieces connected otherwise? Oct 25, 2017 at 18:50
  • @JoeLaFrance: Huh? Each grounding rod has to be whole and in one piece. They come that way from the supplier. I'll at photos of a rod and a clamp.
    – wallyk
    Oct 25, 2017 at 20:54
  • 1
    I had to re-read your post. I get it now, and really appreciate your help. Oct 26, 2017 at 0:33
  • 2
    The picture of a green clamp wallyk posted is what we call an "acorn" clamp.
    – ArchonOSX
    Oct 26, 2017 at 0:56
  • @ArchonOSX: Why is that called an "acorn clamp"? Does that look like (or taste like) an acorn?
    – wallyk
    Oct 26, 2017 at 5:36

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.