Another sub-panel in the garage thread.

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  #1  
Old 10-24-10, 09:43 PM
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Another sub-panel in the garage thread.

I am Installing a sub-panel in my garage a 100 amp square d homeline. I am running it on a 50 amp breaker from my 125 amp main. I will only be using half the available breaker slots. I was given about 850 feet of (new) 6 awg wire and a roll of 8 awg for the ground. My distance is between 60 to 75 feet max through my attic .

1. I am using 3/4 conduit also free! How many wires can fit of this size? (three #6 and one #8?)

2. since I have so much wire can I double the number of wires? (four #6 and two #8) or will that not fit or is ill advised? meaning using two wires as one to increase capacity to maybe utilize a 70 amp breaker?

3. what will #6 wire carry 50 amp, 60 amp?

I assume that the doubling of wires is not permitted but I am not sure. Any help is greatly appreciated.
 
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Old 10-24-10, 09:52 PM
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Assuming the insulation on the wire is type THHN, THWN or THWN-2 you could have up to four #6 wires in a 3/4 inch conduit so three #6 plus one #8 is okay. Be sure there are no more than 360 degrees of bends in the conduit between access points, either a conduit fitting Tee, or Ell fitting with cover or a junction and pull box. Use plenty of wire pulling lubricant when pulling the wire and pull all wires at the same time.

Wire sizes less than 1/0 may not be paralleled. No exceptions.

#6 type THHN, THWN or THWN-2 has an Ampacity of 65 amperes at 75 degrees Celsius.
 
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Old 10-24-10, 09:56 PM
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Awesome help! Thanks for the quick reply
 
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Old 10-24-10, 10:11 PM
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Thought I once read that when more than 3 wires are utilized in a raceway (conduit in this case), de-rating of ampacity must always be taken into account.
 
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Old 10-24-10, 10:32 PM
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Originally Posted by sidecutter View Post
Thought I once read that when more than 3 wires are utilized in a raceway (conduit in this case), de-rating of ampacity must always be taken into account.
They do and the number of % of derate will depending on the numbers of conductors in the conduit and type and tempture { in few case it will affect it }

4 to 6 conductors - 80%
7 to 9 conductors - 70%

But becarefull some local codes may not allow more than 9 conductors { Chicago is one of few spots I know they will go that way }

Merci.
Marc
 
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Old 10-24-10, 10:47 PM
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Merci Marc____Hope your in good health. Herb
 
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Old 10-25-10, 12:46 AM
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Originally Posted by sidecutter View Post
Thought I once read that when more than 3 wires are utilized in a raceway (conduit in this case), de-rating of ampacity must always be taken into account.
That would be more than three current-carrying conductors. In this example the fourth conductor is the equipment grounding conductor which is NOT a current-carrying conductor execpt under fault conditions therefore no derating is necessary. There are also certain circumstances where a neutral conductor is not considered a current-carrying conductor such as multi-wire branch circuits because the neutral only carries the unbalanced current between the "hot" wires.
 
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Old 10-25-10, 11:38 AM
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Originally Posted by sventinker View Post
I was given about 850 feet of (new) 6 awg wire and a roll of 8 awg for the ground.
One techical issue here is that the neutral wire must be white and the ground must be green or bare. The code officially does not allow #6 or smaller wires to be remarked with colored tape; however most inspectors are flexible on this. If the job is inspected I recommend getting the verbal okay first or he could make you pull out the neutral and and ground repull conductors in the correct colors.

3. what will #6 wire carry 50 amp, 60 amp?
Assuming copper and assuming THHN/THWN-2 (please post back if this assumption is wrong). In this case 65A, which you could round up to a 70A breaker if you wanted. There is no need to go above 50A or 60A if that's all the power you need.

I assume that the doubling of wires is not permitted but I am not sure.
Doubling (paralleling) of conductors is not allowed in this case. You could install a second subpanel right next to the first one if you really wanted to use up the free materials. I would probably use what I needed and sell or donate the rest to essentially get a free project done.
 
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