subpanel and ground

[ms23410]

I am writing because I have a few basic questions about the installation of a Siemens 125 Amp Subpanel, Model E0408ML1125SU.

I am installing the subpanel in a workshop/shed located 82’ from the house. I will have a licensed electrician make the final connection to the main, but I have a very strong desire to have as much of the other work properly completed before the electrician makes the final connection. I am the kind of person that really wants to understand the process and love taking on new challenges.

My plan will be to have all of the outlets and lights in the workshop installed and wired myself. That part I understand and am very competent in completing. I would then have the electrician inspect the entire system before he makes the final connection to the main. I hope with this information someone can answer a few basic questions concerning the subpanel.

I will be feeding the subpanel with #8/3 with ground UF cable run underground in conduit. The total run of cable will be about 90’.

Here is my question: I have read every do-it-yourself book on wiring I can find and can’t seem to get a clear answer as to how to do the ground in the subpanel. Can I use the standard neutral/ground bus bar that comes installed in this panel and not worry about a grounding rod. Or do I need to install a separate grounding bus bar in the panel and ground it to a grounding rod? If this is the case, what do I do with the ground wire coming from the main?

It would be very helpful if someone could direct me to photographs or diagrams of the subpanel properly grounded.

[HayZee518]

wire size 8/3 is good for 40 amps. the bare wire that breaks out of the UF cable connects to an auxillary ground bus which you must install in direct contact with the enclosure. The neutral bonding screw is not used. The earth driven ground rod's wire goes to the aux ground bus along with the UF cable's ground.

[kactuskid]

First off, you need to use the proper size wire. For a 125 amp breaker you will need to install 1 AWG copper THHN/THWN wires in plastic conduit. This must also be buried 24". The ground wire must also be insulated. ABSOLUTLY "NO NM Cable" for this job. And NO NM cable should be installed in conduit anyhow. You need and want a 4 conductors installed between your main panel in the house and the subpanel in the garage. Then you also need to install 2 ground rods at the garage. Both the grounds from the ground rods and the ground wire from the house will be attached to a separate ground bar that you need to install inside your subpanel. Also make sure that the green bonding screw that connects your neutral buss bar to the panel is removed. The neutral buss bar must float above the ground and remain separated from the groundbar and the panel frame. Here's an excellent link that'll show you all the requirements for installing a subpanel in your garage and how to connect the grounds and feed cable.

http://www.selfhelpandmore.com/homewiringusa/2002/accessory/detgarage/index.htm

Sounds to me like you need to contact a licensed electrician FIRST and then you should get a copy of your local codes along with a permit. Ask back with any questions you may have.

[HayZee518]

kactus - read the post. He's got a 125 amp panel BUT he's feeding it with 8/3 - 8/3 is 40 amps four wire UF. He's not running 125 amps to the panel.
By the way ms UF cable is for direct burial NOT in a conduit. If you want the conduit route use thw for your feeder #8 ga.

[kactuskid]

Hey Hazy, I did read the question, and from what it says to me is that he's installing a 125 amp subpanel and running 8/3 cable to it. Nothing said from him about only using a 40 amp breaker. Can't take nothing for granted. Just trying to cover his behind, and ours.

[ms23410]

Thanks guys, this was helpful