Garage Sub-Panel Feed Cable

[Underdog57]

I have a 200 amp main panel at my house and want to feed a 100 amp panel in the garage. The feeder cable will be buried about 20'. I know the sub-panel ground and neutral bars must be isolated. I plan on putting a 100 amp breaker in the main panel to feed the sub panel. I have several questions,

1. What size and type cable do I need? (I think I need #2 wire?)

2. Can I use a 3 wire cable (2/2/2) and put a ground rod in at the sub panel or should I use a 4 wire cable (2/2/2/4) and carry the ground from the main panel to the sub panel?

3. Is Aluminum Cable ok to use?

4. If I used mobile home feeder cable and put it in pvc conduit could it be buried?

5. How deep should it be buried (frost line is 42" here) ?

I'm sure I'll think of something else later, but I'll put this out there for now.
Thanks in advance

 

[LD1]

Don't know what's code, I am not a residential electrician, but can tell you how I would do it.

2-2-2-4. Two hots, neutral, and ground. As well as a ground rod at the garage.

Aluminum feeder is fine, used everyday. But there are some regulations in putting feeder in conduit. Amp ratings are basically how hot the wire is allowed to get before the insulation fails.

Wire made to be buried directly in the ground, assumes the ground is gonna keep the wire cool. When you burry that wire in a plastic (insulated) tube, that wire "can" get too hot.

Depth....thus ain't water. Frost depth is of little concern. Typically code is 24" for a secondary feeder

 

[Deere Dude]

I just put one in last year and the consensus from what I remember at the time is no ground rod in the garage. The ground must go back to the main panel and the garage panel must be unbonded, in other words the ground and neutral must not be co-joined.

But with this stuff I would like to hear from qualified electricians of which I am not. I just did what made sense to me after reading from TBN and other forums.

 

[Ron50]

2/2/2/4 up to 100'. Suggested 1/1/1/2 beyond 100' to minimize voltage drop during higher use, Do not bond neutal and ground in a sub panel, hence 4 wires. You do need to ground the panel with a ground rod or copper wire in the footing depending on your local code.

 

[Qapla]

You may get a variety of information and suggestions here on the form. This is a great place to get some very qualified direction.

That said - in the long run, you need to use whatever YOUR local code requires - ask them.

 

[varmint]

From the little I know, Ron50's advice sounds dead on. Sometimes code officials can be too fussy for your own good.

We had a PV solar system installed, and the electric code requirements were over the top (since rationalized and simplified) mostly because it was new territory for them, so they erred on what they thought was the side of caution. Cost us extra money, though. We probably have the best grounded system in the area- I think 4 new ground rods got installed- two new ones at the house panel, one where the feed entered the house, and one at the barn, where the panels are. They wanted the demand water heater, which was within sight of the panel, to have bonded grounds installed on any copper piping, even though the well feed and most of the house piping is plastic.

 

[Underdog57]

Thanks guys, very good info. Got all the parts and the trench is dug (24"). Got the 2/2/2/4 mobile home feeder cable for direct burial (Menards had a 30' remnant for $35.) Gonna work on it tomorrow.

 

[jimmysisson]

Clean sand only around that cable. Very unpleasant to have a frost-pushed rock take out your power in winter. BTDT. Jim

 

[varmint]

Clean sand only! Especially around buried copper gas pipe. Stupidly let a vibratory compactor run over our gravel drive, and the gas line... a rock got "compacted" into the line, and bingo- leak.