Another subpanel grounding question

[Korey Atterberry]

Hey all-

First off, I apologize for asking a question that seems to be asked a lot around here. I've been reading posts on the subject for about 2 hrs this morning, but I'm missing something.

My situation: I have a main panel in my house, and I have an attached garage which my dad and I put a 60amp subpanel in. Now I know that I need to keep the neutral and ground separate in this subpanel (I've seen LOTS on this topic), but what I'm missing is, where do I connect the grounding bar in the subpanel? Grounding rod, ground wire back to the main panel, don't need it?

Right now we've got (and I know our setup is wrong) the main lug subpanel with just one bus bar, which is not connected to the case. Both the ground and neutral wires for the branch circuits for this panel are connected to this bar. We have two hot wires and one neutral run back to the main panel where I have a 60amp breaker. The inspector has been out and given the system his blessing (which makes me doubt him a bit). My dad did most of the work, I had second thoughts after the inspection, so that's why I'm here.

So to correct the situation, I presume I need to get a grounding bar kit for the subpanel and hook the branch circuit grounds to it (keeping the neutral isolated from the ground). But what do I hook the grounding bar to? Do I need a grounding rod or a ground wire back to the main panel?

Thank you in advance, Korey

[Greg]

You need a 4th wire back to the panel. It can be bare but the neutral must be insulated.

[zxcvbob]

You have three wires from the service panel to the subpanel? Is the neutral wire insulated? Is this a multiwire cable or individual wires in conduit, or individual wires taped together in a bundle, or what?

Let's assume for a minute you have 2 black wires and a white or gray wire. Run a bare or green wire back to the service panel, and if possible run it with the old wires (but if you can't don't worry about it.) Use this new wire for the ground and separate the grounds from the neutrals in the subpanel. You'll probably need a grounding kit. Don't forget to remove the bonding screw or strap that currently grounds your neutral bar to the metal subpanel cabinet.

If you have 3 insulated black wires (or 2 blacks and a green), wrap white tape around the ends of the neutral wire and proceed as above.

If you have 2 black wires and a bare wire, I'm not sure what the best way to handle it is without seeing it. You need another insulated wire for the neutral.

Bob

[xrongor]

in addition to what has been said, i believe code states that if your garage/shop is in a seperate building, not only do you need to ground it back to the panel in the house via a wire, but you need two grounding rods sunk in the ground at the garage.

so in short, i think you need both if you want it to be 'correct'

randy

[SQLit]

ground bars are attached to the can of the panel in the provided holes. The neutral bar must be isolated from the can. Get a ground bar/insulated neutral kit for the panel you bought. You need to carry a code gauge ground wire from the service to the subpanel. Driving an ground rod at the subpanel is allowed and is called a supplemental ground. It must have a ground wire as large as the service has. If you drive a ground rod and do not have a ground wire properly installed you have created a ground loop. Not a good safe way to use electricity. But then again there are a lot of people that choose this method.

[John Hines]

The grounding bar screws into the box, there should be a few small holes tapped into them, so that the ground bar can bolt right in.

It connects to the metal electrical box, via the mechanical connection of the screws that hold it to the box.

If you can not get one that fits properly, one can be added with self-tapping sheet metal screws, which make a good mechanical connection.

[zxcvbob]

Actually, if the subpanel is in a separate building, you have the option of *not* running 4 wires back to the main panel. There are restrictions on this 3-wire method, of course. All this is moot because OP said it was an attached garage.

Bob

[Korey Atterberry]

Thank you all for your help. To answer some questions and clarify, I have an attached garage, and I ran three insulated black wires in the trench. One wire we taped white to make a neutral. No other wires in the trench. I now have the grounding bar I need for the subpanel.

Can anyone explain why I need to run the ground back to the main panel, as opposed to sinking a couple of grounding rods outside near the subpanel? These rods would be about 60-70 feet from the rods at the main panel. Since the inspection is done I have mostly filled my trenches, so adding another wire will be a chore, but I want to do the right thing for safety (I guess meeting code is not as much of an issue seeing as the original setup passed inspection...)

[zxcvbob]

I would run a #8 green wire or a #6 bare wire back to the service panel by whatever route was easiest -- just staple it to the studs and joists. The ground wire is supposed to be run with the current-carrying conductors, but there is an exemption for adding a ground to "old work." #8 wire is easy to use but you're supposed to protect it from damage with a conduit (but you could skip that if it's not gonna be inspected and you promise to be careful never to abuse that wire ;-) #6 solid wire is a bitch to work with, but it can legally be run without a conduit.

Bob

[Korey Atterberry]

Thank you to all who replied. Based on your advice I'm going to run the #6 solid bare wire back to the main panel. I figure the #6 will be easier to push up/down the short length of conduit from the ground to the service elbow. I wish either myself, my dad, or the building inspector would have caught the mistake earlier, since I have to re-dig my trenches! Oh well, our clay was hard to dig the first time, but at least it is also pretty hard to tamp well, so the digging will go easier this time! I can't go through the house or garage since it's all finished (which coincidentally is the same reason I needed the subpanel in the first place).

Thanks again, Korey