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Exterior electric feeder to detached garage: Copper to Aluminum

Exterior electric feeder to detached garage: Copper to Aluminum

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Old 09-17-14, 08:27 PM
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Exterior electric feeder to detached garage: Copper to Aluminum

Hello, Hoping someone can help clarify....

I've got a 24" trench in the ground going out to my detached garage (about 150'). I originally purchased a 125' UF-B direct burial copper 6/3 w/ ground to drop in the trench. Unfortunately the length was incorrectly measured

so I've picked up a 2-2-2-4 Aluminum direct burial service wire (and will return the too short 6/3 copper). This aluminum wire is rated at 100 amps. My concern is: the existing feeder inside the house that was roughed in during construction is a dual breaker 50 amp 240 volt circuit and the wire is a copper NM-B Romex 6/3 copper w/ ground. It's stubbed out the side of the house.

I need to find a box and method to terminate the 2-2-2-4 ALUMINUM wire to the existing 6/3 COPPER w/ ground Romex. Ideally this would be a disconnect box with separate terminal strips for Hot, Neutral, and Ground.

Having difficulty finding the correct box - most that I've seen are just two wire boxes... 240v hot plus a ground terminal block..... No neutral wire....

Any recommendations for the proper box and/or lugs, split bolts etc. to get this job done?
 
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Old 09-17-14, 09:28 PM
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Having difficulty finding the correct box - most that I've seen are just two wire boxes... 240v hot plus a ground
A 6x6 weather proof box will be fine. Use split bolts rated for copper and aluminum connections (they have a separator so the wires don't touch). Use anti oxidizer on the aluminum wire. Wrap first with rubber tape then PVC electrical tape.
Ideally this would be a disconnect box with separate terminal strips for Hot, Neutral, and Ground.
No disconnect at the house is needed except the 50 amp breaker in the main panel. A disconnect is needed at the garage if more than six breakers in the subpanel. This can be done by using a main breaker type panel. Note some URD is not rated to be run in a building so you may have to transition where you enter the garage. If it just says URD you can't use inside but USE/XHHW you can. (Pros correct me if I'm wrong.)
 

Last edited by ray2047; 09-17-14 at 09:51 PM.
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Old 09-18-14, 12:00 AM
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I did not check the box size but would advise Polaris connectors over split bolts and tape.
 
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Old 09-18-14, 04:20 AM
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Sometimes my age creeps into my replys. PCBoss gave the better answer. Use Polaris connectors in the box and verify a 6x6 will be big enough.
 
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Old 09-18-14, 05:27 AM
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Thanks guys - I will look into the polaris connectors today. I did pick up a 12 slot sub-panel with 50 Amp main breaker for the far end. If no disconnect is needed at the near end (other than at the main panel) that should work great. The box is 6x6x5deep - but if I need to go larger to support the better termination, I'm fine with that.
 
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Old 09-18-14, 06:08 AM
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Normally it would be cheaper to buy a 100 amp main breaker service panel kit. The main breaker and some branch circuit breaker are included. A 50 amp main breaker panel is a rare animal and therefore costs more. (Since the breaker in the sub is only used as a disconnect it doesn't matter if it is 100 amp.) Maybe you can return what you bought and get a cheaper solution.

Did you also buy a ground bar. You usually need to buy and add though. In addition you need a ground rod at the subpanel and a #6 wire (copper only) to connect it to the subpanel.
 
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Old 09-18-14, 06:21 AM
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I did pick up a 12 slot sub-panel with 50 Amp main breaker for the far end.
If that 50 amp breaker is just a plug-on version to attach to the bus and backfeed as a main breaker, you'll also need a main breaker retaining kit to hold it in place. I haven't checked the size of the box either, but 6 X 6 seems a bit tight to me. I don't think most 50 amp breakers will accept a #2 conductor, might be best to replace it with a 100 amp breaker, it's just a disconnect.
 
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Old 09-18-14, 06:41 AM
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I think the panel was on sale and not too crazy expensive - I see your point though. I did not pick up the ground rod though - can that be inside or outside and can it be buried (not visible)?

thanks
 
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Old 09-18-14, 07:21 AM
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The ground rod is driven flush with the ground. Do you have a ground bar for the panel?

You normally use a main lug panel for a back fed panel. Is that what you have not a main breaker panel? As mentioned if back fed you will need a breaker hold down bracket.

Main lug panel. Notice the lugs on top.
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A main breaker panel would have a large breaker instead of lugs.
 
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Old 09-18-14, 07:41 AM
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I've got the main breaker brakets to hold them down tight to the panel. I also have the ground bar for inside the panel. So my 6 awg ground wire connects to that and I can just use a split bolt to terminate on the ground rod? If flush to the ground is OK I will just hammer it down next to the foundation of the garage (concrete floor 30 x 40 shed). I was planning on coring through the concrete floor and bringing the electric up through the floor - can my ground wire go through that same hole out to the ground rod?
 
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Old 09-18-14, 09:05 AM
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I can just use a split bolt to terminate on the ground rod?
No you use a ground wire clamp.

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I've got the main breaker
No, back fed breaker that serves as a disconnect. Since the wires may be two large you may need to swap it for a 100 amp or compare price to a main breaker panel kit. When comparing price be sure to add the price of branch circuit breakers you will need to buy for the main lug with the price of breakers already included with a main breaker panel kit.

Just for information: Actually the main lug panel with a 50 amp back fed breaker was a good choice for 6-3 because #6 is sometimes too small for a 100 amp breaker and you have to pigtail with larger wire.
 
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Old 09-18-14, 11:23 AM
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I found some polaris connectors - they're pretty spendy, but probably worth it in the long run. Will pick those up with the ground rod and accessories tonight. I will check the sub-panel 50amp breakers for wire size - if too small I'll exchange for 100amp units.... I was thinking 6awg copper originally which is why I went with those... will measure twice next time.
 
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Old 09-18-14, 11:25 AM
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The Acorn clamp above on the left works better on a ground rod. The silver one is fine for an exposed pipe like a water line.
 
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