Garage Panel Feed - Aluminum?

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Old 03-06-16, 06:57 AM
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Garage Panel Feed - Aluminum?

Currently my garage is fed by one 20amp circuit and that is just not enough for my use. I plan on adding a small sub panel box in the garage fed by a 50 or 60 amp breaker. Question being, can I feed this with #4 aluminum? Approx. length is about 80' or less from the panel inside to the garage. I've always used copper, but if I'm allowed to use aluminum it is a far cheaper alternative. 6/3 UF is over $3/ft whereas the 4/4/4 AL is around $1-$1.50/ft.
 
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Old 03-06-16, 07:03 AM
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Aluminum is fine but you need a 4 wire feed and the existing circuit needs to be abandoned. I recommend aluminum 2-2-2-4 Mobile Home Feeder (MHF). As a branch feeder the #2 Al is good for up to 90A, but you can feed it from a 50A or 60A breaker if you want to. It sells for around $1.50 ft. It's a direct bury cable but it's best to put it in conduit underground, but it does have to be in conduit where installed inside.

MHF can be purchased online... http://www.wireandcabletogo.com/2-2-...der-Cable.html

If you do use three #4 Al you need to add at the least a #8 Al for the equipment ground.
 
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Old 03-06-16, 07:26 AM
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As far as the separate ground, the ground and neutral is not separated in the main box (passed inspection). Would I still need to do a separate ground? I was planning on installing a separate ground rod for the dwelling.
 
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Old 03-06-16, 07:36 AM
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At the main panel if that's the first main disconnect point the grounds and neutrals are together (bonded). You should have an electrode grounding wire that connects to the ground/neutral bar in the main panel that runs to two grounding rods. The detached garage needs the same (2 rods) but the grounds and neutral are separate with the neutral being isolated (not bonded to the panel/ground).

I forgot to ask is this garage detached? If not then everything I've said is wrong. You mentioned UF cable so I assumed detached.
 
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Old 03-06-16, 07:49 AM
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Yea it's a separate building. So what I'm gathering I still need to connect a ground at the main building? I'm usually good with electrical, but have never hooked up an outside dwelling. When I lived in the South I knew people would just run 3 wire cable and call it good.
 
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Old 03-06-16, 07:57 AM
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NEC changed some years ago and 4 wire feeders are now required. When you say ground at main building are you talking about adding a grounding electrode system ( ground rods). I assume you have ground wires in your branch circuits that are on the neutral/ground bar in the main panel. If you're talking about the equipment ground from the garage back to the main panel then yes that's the 4th wire you need and it connects to the ground/neutral bar in the main panel and the ground bar in the sub.

Here's a good diagram.....

http://www.garagejournal.com/forum/p...ictureid=16967
 
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Old 03-06-16, 08:11 AM
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That diagram was exactly what I was planning to do after thinking it over. I was going to do a separate ground rod at the garage, but that would not be correct.
 
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Old 03-06-16, 08:26 AM
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I was going to do a separate ground rod at the garage, but that would not be correct.
If it is a detached garage it would be correct. Is your garage detached?
 

Last edited by ray2047; 03-06-16 at 10:17 AM.
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Old 03-06-16, 08:45 AM
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I was going to do a separate ground rod at the garage, but that would not be correct.
Pay close attention to the diagram I linked, it's for a detached structure. Since your garage is detached you do need ground rods off of the subpanel in the garage. The main panel should also have grounding rod(s).
 
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Old 03-06-16, 09:33 AM
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Is your garage detached?
See post #5

I was going to do a separate ground rod at the garage, but that would not be correct.
A ground rod is required for a separate structure along with the ground with the feeder. A Ground rod does not provide a ground, it is only to dissipate high current events such as lighting strikes or surges.
 

Last edited by Tolyn Ironhand; 03-06-16 at 09:57 AM.
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Old 03-06-16, 09:41 AM
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Ah, thanks guys for clearing that up!
 
 

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