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Old 08-24-2011, 08:04 PM   #1
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How many amps can 6 THW Copper handle


Hi,

I have wire that feeds into my garage load center from the house. The wire jacket says "6 THW 600 volt AMMCO". I am wondering how many amps this can handle.

However, the wire enters into the house into a service box. For whatever reason, the wire that it is connected to that runs back to the main panel is 10 guage aluminum wire. It is my understanding that the 10 guage aluminum can only handle up to 25 amps. Currently there is a 50 amp double pole breaker in the main panel.

So basically what I am wondering is if I replace the 10 guage aluminum wire back to the main panel with more 6 THW, what is the maximum size of the breaker I can use in the main panel?

Also, if I bought new wire would it still be called THW, or is that something out of date?

Hope that made sense.

Thanks in advance.

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Old 08-24-2011, 08:19 PM   #2
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How many amps can 6 THW Copper handle


#6 copper THW is good for 65 amps. But your cable may be only 55.

You can use Romex and keep the 50 amp breaker.

It may possible to increase to a 60. Do you need 60?

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Old 08-24-2011, 08:36 PM   #3
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How many amps can 6 THW Copper handle


I think I can get away with 50. I really just want to be able to take full advantage of the wire that is already going out to the garage. However, I know I can't do that with the aluminum wire that is there right now.

What I really want to do is replace the box in the garage that only supports 4 breakers. If I am only running 50 amps to the garage, is there a limitation on the number of circuits I can run? Someone told me that if I had 3 20 amps circuits it would be too much. I don't plan to run much load on any of the circuits, but in the event of tripping a breaker I don't want too much going out, if that makes sense.
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Old 08-24-2011, 08:42 PM   #4
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How many amps can 6 THW Copper handle


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Originally Posted by dw1256 View Post
I think I can get away with 50. I really just want to be able to take full advantage of the wire that is already going out to the garage. However, I know I can't do that with the aluminum wire that is there right now.

What I really want to do is replace the box in the garage that only supports 4 breakers. If I am only running 50 amps to the garage, is there a limitation on the number of circuits I can run? Someone told me that if I had 3 20 amps circuits it would be too much. I don't plan to run much load on any of the circuits, but in the event of tripping a breaker I don't want too much going out, if that makes sense.
I assume that this a 4 wire cable.

The person was wrong.

As long as the circuits are "lightly loaded", you can put in a bigger panel. A 8 space is common on a 50 amp breaker.
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Old 08-24-2011, 08:59 PM   #5
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How many amps can 6 THW Copper handle


Yes, it is 4 wire. Two hot, neutral, and ground.

My plan was to swap it out for a main lug panel with 8 spots.

I think this is my last question. There are also some other wires that run out from the basement to the garage that power lights on side of the garage and the roof. They do not get any power from the load center, but they do run through the panel as if it were a junction box. Any idea if that is not allowed?

Thanks again. You have been very helpful.
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Old 08-24-2011, 09:09 PM   #6
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How many amps can 6 THW Copper handle


Is the garage attached or a seperate structure?
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Old 08-24-2011, 09:13 PM   #7
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How many amps can 6 THW Copper handle


60a to a workshop is common and usually ample power. I have 60a on #6 to a nearly full 12 slot panel in my workshop/garage. There I have a MIG welder, air compressor, lights, table saw, misc. power tools, heater, etc. Also powers my motorhome when parked at home. All works great.
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Old 08-24-2011, 09:15 PM   #8
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How many amps can 6 THW Copper handle


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Originally Posted by dw1256 View Post
Yes, it is 4 wire. Two hot, neutral, and ground.

Good


My plan was to swap it out for a main lug panel with 8 spots.

That is fine. You need a separate ground bar also.


I think this is my last question. There are also some other wires that run out from the basement to the garage that power lights on side of the garage and the roof. They do not get any power from the load center, but they do run through the panel as if it were a junction box. Any idea if that is not allowed?

That is legal. Panel should be labeled to indicate this for safety.



Thanks again. You have been very helpful.
You are welcome.
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Old 08-25-2011, 02:15 AM   #9
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How many amps can 6 THW Copper handle


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Originally Posted by Code05 View Post
#6 copper THW is good for 65 amps. But your cable may be only 55.

You can use Romex and keep the 50 amp breaker.

It may possible to increase to a 60. Do you need 60?
I just don't want to step on your toes but I hope you did not read the wrong tempture chart due the OP mention THW not the THHW IIRC the THW is on 75C rating not on the 90C

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Old 08-25-2011, 05:06 AM   #10
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How many amps can 6 THW Copper handle


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Is the garage attached or a seperate structure?
Separate structure.
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Old 08-25-2011, 05:10 AM   #11
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How many amps can 6 THW Copper handle


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I just don't want to step on your toes but I hope you did not read the wrong tempture chart due the OP mention THW not the THHW IIRC the THW is on 75C rating not on the 90C

Merci,
Marc
What does it mean if it is on the 75 rating?
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Old 08-25-2011, 08:25 AM   #12
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How many amps can 6 THW Copper handle


Quote:
Originally Posted by frenchelectrican View Post
I just don't want to step on your toes but I hope you did not read the wrong tempture chart due the OP mention THW not the THHW IIRC the THW is on 75C rating not on the 90C

Merci,
Marc
65 amps is the 75C ampacity for THW. His cable is probably limited to 55 amps at 60C.
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Old 08-25-2011, 08:27 AM   #13
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Separate structure.
You need 2 ground rods if they are not there already. Separate grounds and neutrals.
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Old 08-25-2011, 08:30 AM   #14
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How many amps can 6 THW Copper handle


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What does it mean if it is on the 75 rating?

You have a code book, it would be easier to explain.

I will see if I have a link.
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Old 08-25-2011, 09:11 AM   #15
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Quote:
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Separate structure.
Panel will require a main if there are more than six breakers.

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