I'm getting different thoughts on this, so ask the people I trust.
I'm putting in my subpanel soon out in the car port. I'm connecting it to the sub panel in my garage on a 50 amp breaker. The subpanel is connected to the main on a 50amp breaker, with '#6 UHF cable, but we also tied a bare wire from the subpanel to the house ground, which is I think where I'm getting confused.
At the carport, I have buried a copper ground bar, and have bare '#6 for connecting the panel to the rod.
Do I have to run 4 lines to connect to the house, or just 3 because I'm grounding the panel in the car port?
I already have 4 lines bought, but before I open them and start running things, I'm just making sure I need all 4.
Not that it matters, but the lines are 6 gauge stranded THHN and will be run through 1" conduit.
I did a similar sub panel run of 8 gauge THHN to my garage on a 50 amp breaker through 3/4" (inner diameter) liquid-tight conduit. I used 4 wires, but since you have the ground already, I (THINK) you would only need 3. I'm still learning some of this electrical stuff, so double check me.
My recommendation would be to return all 4 wires, and get a 500' spool of 8 gauge. I got mine through Lowe's and it came out to be a really good deal. Plus you'll only need 3 wires. Apparently 8 gauge THHN, individual strands through conduit, is rated for 55 amps.
Lowe's 500' 6-gauge
Lowe's 500' 8-gauge
Though, depending on where you got the original wire, some return policies on wire are strict...
armchair electrician here:
run all 4 wires, but you can never have too many grounds.
My garage is supplied with a pair of 4g hots, a 4g common, and is grounded to it's own ground rod. It was approved. I ran 70 amps out there for overkill
I went with 6 for the length of the run, 8 isn't thick enough if I run 240 in the carport to risk it.
6 will give me 60 amps to 165 feet, I'm at 95 feet right now, which is at or past what 8 is rated to.
The 55 for taking back the one roll of 6 is better than replacing it all with something thinner that might not take the current if I hook up a welder or big compressor.
I won't be pulling cable till Sunday at the earliest so I have time to do more research. Just kills me I used to know all this crap, but having not used these skills in 10 years, I might as well be a first timer.
I'm a software guy, not a EE or an electrician. All I know is that if you're pulling cable, ALWAYS pull more than you think you'll need. :)
You need to run all 4 conductors, but I would go ahead and tie to the buried ground bar.
rustyvw wrote:
You need to run all 4 conductors, but I would go ahead and tie to the buried ground bar.
So much for cheaping out. An electrician friend came by tonight to get some beer I don't drink anymore and said pretty much the same. Oh well, I got lube and a pull rope. Hopefully I can get this done this weekend.
Is your wire on spools, or is it cut and coiled?
IIRC you bought a new panel. That panel should have come with a green screw, about 1 1/4" long. Ask your electrician friend if you should install it after you decide on your grounding.
You need all 4, but I'm pretty sure the bare wire can be smaller than the others. At least thats how I did all of mine and I installed what the inspector told me to install. I ran mine in 2" schedule 80 PVC pipe. Stuff is cheap enough and gave me the satisfaction of knowing I have options without digging it up later. I even ran a separate spare 2" pipe from the house to the garage which I later used to run phone and cable wires in.
Robbie wrote:
armchair electrician here:
run all 4 wires, but you can never have too many grounds.
Mr. Lucas vehemently disagree with you.
Oh, he would also like to encourage the use of bullet connectors.
paranoid_android74 wrote:
Is your wire on spools, or is it cut and coiled?
IIRC you bought a new panel. That panel should have come with a green screw, about 1 1/4" long. Ask your electrician friend if you should install it after you decide on your grounding.
cut and coiled 
PITA that it is. Just checked the weather, rain all day tomorrow, 30 on Sunday, so I guess laying it out in the sun to straighten up is out.
I kinda figured I needed it, but I've seen a few people who have done it without, so I thought I'd ask the hive about it. I also assumed since it hit 80 today, this trend would continue and I'd get done this weekend.
tr8todd wrote:
You need all 4, but I'm pretty sure the bare wire can be smaller than the others. At least thats how I did all of mine and I installed what the inspector told me to install. I ran mine in 2" schedule 80 PVC pipe. Stuff is cheap enough and gave me the satisfaction of knowing I have options without digging it up later. I even ran a separate spare 2" pipe from the house to the garage which I later used to run phone and cable wires in.
It's just what I have on hand. I have maybe 10ft of bare 6 guage hanging in the garage. The bury length is 60 ft underground, followed by 10 ft up and 18 to go across the garage ceiling, and 6 to the panel. Damn, that's cutting it close. I have 140 ft of 1", so I'm actually considering running a second for an airline or now I'm thinking ethernet cable at some point in the future, but just to have.
In reply to RevRico:
Well shoot. It might be a little extra work then.
Remember that on a sub panel the ground and neutral bars have to be separate, not bonded together. Do not drive the screw through the neutral bar into the panel structure like you would on the main panel. Do not mix your neutral and grounds together on the same bar either.
