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Old 05-27-2010, 02:33 PM   #1
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Adding 100amp Subpanel for basement


Hello,
This is Raj from Atlanta, GA. I am planning to add a GE 100amp subpanel to finish the basement. Currently I have a 200amp main panel.

Its a 1300sq.ft basement, with possibly heat pump (possibly 10kW heat strip). I was told that a 100amp subpanel would be good enough (upstairs I have gas furnaces).

I am planning to get the GE 100amp contractor panel from Home depot. The subpanel will be 15 feet away from the mail panel (both of them inside the basement). I am thinking to use 2 gauge wire for the hot. The following are the questions I have:
1. Should I run two hots from main to sub, please confirm the wire size.
2. What wire size should I use for neutral and ground?
3. Should I run all the above wires thru a conduit even though itís a inside and dry run?
4. Should I have one breaker or two breakers in the main panel (one 100 amp?)

Any help is appreciated Thanks in advance...

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Old 05-27-2010, 08:30 PM   #2
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Adding 100amp Subpanel for basement


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Originally Posted by trajendra_babu View Post
Hello,
1. Should I run two hots from main to sub, please confirm the wire size.
2. What wire size should I use for neutral and ground?
3. Should I run all the above wires thru a conduit even though it’s a inside and dry run?
4. Should I have one breaker or two breakers in the main panel (one 100 amp?)

Any help is appreciated Thanks in advance...
You can get away with smaller wire if you use THHN in conduit (as opposed to cable pre-bundled). I'd run it in PVC conduit.

2 Hots (red/black): #3 THHN
1 Neutral (white): #3 THHN
1 Ground (green): #6 THHN

You must use a 2-pole (240v) 100-amp breaker in your main panel to feed the subpanel. The sub can be a main breaker panel or a main lug panel (no shutoff in the sub). If you are buying a contractor pack, it probably includes a main breaker too. This is fine. Just make sure your two hots are fed off a 100-amp double-pole breaker, and each hot coming out of the breaker should be on its own hot bus bar.

The neutrals and grounds in your subpanel MUST be on separate bars, ie. NO connectivity between the two bars. Main breaker panels usually come with the two bars connected with a jumper. This must be removed to use it as a sub. You can test for (lack of) continuity between the two bars with a continuity tester before installing the unit or connecting any wires.

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Last edited by secutanudu; 05-27-2010 at 08:34 PM.
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Old 05-27-2010, 09:56 PM   #3
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Adding 100amp Subpanel for basement


Thank you Andrew
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Old 06-08-2010, 07:27 PM   #4
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Adding 100amp Subpanel for basement


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You can get away with smaller wire if you use THHN in conduit (as opposed to cable pre-bundled). I'd run it in PVC conduit.

2 Hots (red/black): #3 THHN
1 Neutral (white): #3 THHN
1 Ground (green): #6 THHN

You must use a 2-pole (240v) 100-amp breaker in your main panel to feed the subpanel. The sub can be a main breaker panel or a main lug panel (no shutoff in the sub). If you are buying a contractor pack, it probably includes a main breaker too. This is fine. Just make sure your two hots are fed off a 100-amp double-pole breaker, and each hot coming out of the breaker should be on its own hot bus bar.

The neutrals and grounds in your subpanel MUST be on separate bars, ie. NO connectivity between the two bars. Main breaker panels usually come with the two bars connected with a jumper. This must be removed to use it as a sub. You can test for (lack of) continuity between the two bars with a continuity tester before installing the unit or connecting any wires.
I changed the location of the subpanel. The wire length is now around 32ft. Do I need to keep the wire in a conduit? If so, what type. Thanks.
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Old 06-08-2010, 07:43 PM   #5
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Adding 100amp Subpanel for basement


THHN wire must be in conduit the entire run
Grey PVC is for electric wires, need matching glue too
32' is not a problem for distance
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Old 06-08-2010, 07:48 PM   #6
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Adding 100amp Subpanel for basement


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THHN wire must be in conduit the entire run
Grey PVC is for electric wires, need matching glue too
32' is not a problem for distance
The wire I got from Lowes 2-2-2-4 Aluminum says "XHHW-2". Does this also need a conduit? Thanks.
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Old 06-08-2010, 07:51 PM   #7
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Adding 100amp Subpanel for basement


I think #2 Alum (according to chart) is only rated for 90a
Are you feeding with a 90a breaker now instead of a 100a ?
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Old 06-08-2010, 07:53 PM   #8
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Adding 100amp Subpanel for basement


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I think #2 Alum (according to chart) is only rated for 90a
Are you feeding with a 90a breaker now instead of a 100a ?
I am feeding 100amp breaker. I did talk to three local electricians who said they would use 2-2-2-4. Please let me know.
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Old 06-08-2010, 07:55 PM   #9
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Adding 100amp Subpanel for basement


I don't use Alum, but according to NEC chart 310.16 #2 Alum is only good for 90a
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Old 06-08-2010, 08:00 PM   #10
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Adding 100amp Subpanel for basement


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I don't use Alum, but according to NEC chart 310.16 #2 Alum is only good for 90a
I shall talk to the an local inspector again. What about the conduit for the XHHW-2 type of wire? The problem is I cannot run the plastic conduit as I cannot get in between the studs. BTW the cable says "TYPE SE" on it... Thanks...

Last edited by trajendra_babu; 06-08-2010 at 08:04 PM.
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Old 06-09-2010, 08:24 AM   #11
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Adding 100amp Subpanel for basement


Type se can be run without conduit.
All the inspectors in my area allow that wire on a 100 amp breaker, but check with the local guy.
If they will not allow it on a 100 amp breaker, find an elcetrical supply and order a 90 amp breaker for the main panel.
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Old 06-09-2010, 11:26 AM   #12
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Adding 100amp Subpanel for basement


In the 90 deg column is lists XHHW-2 as 100 amps. so if the 100 amp breaker is 90 degs. then it should be good. Check with your inspector though.
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Old 06-09-2010, 11:35 AM   #13
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Adding 100amp Subpanel for basement


Under the 2008 NEC SE and SER cable is rated the same as NM when for wiring other than service equipment. It's ampacity is rated using the 60 deg C column of 310.16. #2 Al is only rated at 75 amps.
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Old 06-11-2010, 06:12 PM   #14
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Adding 100amp Subpanel for basement


Here is the top view of my main panel:
http://img811.imageshack.us/img811/3199/img0340.jpg

How should I get the 2-2-2-4 Al cable out from the main panel? Any suggestions please? Thanks...
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Old 06-11-2010, 06:19 PM   #15
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Adding 100amp Subpanel for basement


Why is there framing in front of the panel ?
You are required to keep an area 30" wide & 36" in front of the panel clear

There also appears to be 3 sets of wires with a black spacer around them?
Are these secured at the breaker case somehow ?


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