Need to install sub panel

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  #1  
Old 12-17-18, 05:13 PM
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Need to install sub panel

I have a 200Amp service. The breaker box (QO) is totally full with tandem breakers in all positions that can take one. I would like to finish my basement so I am going to have to add a sub panel. The basement is framed for 6 rooms including what will eventually be a full bathroom.

The sub panel would be located a couple of ft away from the existing panel. I understand the info wrt wiring the sub panel to the main panel including the grounding.

What size/type sub panel should I consider?

I will have to relocate a couple of circuits from the main panel to the sub panel to make room for the breaker that will feed the sub panel. What should the size of the breaker feeding the subpanel be 50Amp? Larger? Smaller
It is doubtful that the circuits I need to relocate will have wire long enough to get moved over to the sub panel. Can I leave the wires in the main box and wire from there to the sub panel.?

I have never has to get a permit and inspection for a project before. This is going to be a fun project and a good learning experience.

Appreciate any comments.
 

Last edited by ijourneaux; 12-17-18 at 06:12 PM.
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  #2  
Old 12-17-18, 06:47 PM
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Typically, a 60 A breaker feeding a 6/3 + ground cable is a good bet for a generic subpanel.

For the panel itself, a 12/18/20 space panel is a good start, it can be a 100A panel (though it will be still protected at 60A). You can get a main-lug panel, but often times it's cheaper to get a panel with a main breaker. Some of them even come in combo packs including some commonly used breakers. It's good form to use the same manufacturer panel as your main so the breakers are interchangeable, but not required.

Then pick the loads you want to move to the sub panel. Easiest is to pull them completely out of the main and into the sub. You can "jumper" them across the panel if you really want/need, but I'm sure your main is already pretty full with wires, so it's usually better to pull them out, even if they need to go into a separate box and extend the cable from there.

Make sure you read up on requirements for all your new basement electrical!

Good luck!
 
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Old 12-18-18, 06:08 PM
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Silly question what does 6 space 12 circuit mean? 6 space in the number of opennings in the panel but is 12 circuit because it allows for tandem breakers?
 
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Old 12-18-18, 06:21 PM
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You got it. 6/12 allows 6 standard size breakers or 6 tandem breakers.

While tandem breakers are fine, I would usually go for a 12/18 or similar since maxing out a panel right up front is usually a bad idea. You don't want to have to install yet another sub panel down the road!
 
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Old 12-18-18, 06:27 PM
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Also keep in mind that most new circuits need AFCI and those breakers are full size only.
 
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Old 12-19-18, 04:29 AM
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Thanks for the clarification on AFCI. Would this normally only apply to the new circuits in the subpanel or will I have to replace the breakers in the existing panel? Will definitely get a larger sub panel.
 
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Old 12-19-18, 08:30 AM
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If you wire new circuits to the existing panel they fall under the AFCI rules. All existing in the old panel should be fine if you don't touch them. Existing circuits moved to the new panel technically fall under the rules as they are "modified" but some inspectors give a pass.
 
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Old 12-19-18, 10:01 AM
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If I read this correctly, the 60amp breaker in the main panel will need to be AFCI (that one is expensive). I am going to have to move two existing circuits from the main panel to the new sub panel so they will need to be AFCI as well. And all new circuits in the sub panel will have to be AFCI.

For the cable connecting the main panel to the subpanel (at most 10-12ft long) 60AMP requires 6AWG 4 conductor. What is the correct way to refer to this wire?
6 AWG 3 Conductors + #8 Ground THHN?

I have a call into the inspector to figure out how to get that process started.
 
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Old 12-19-18, 10:57 AM
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No need for an AFCI breaker on the 60A sub panel breaker. Just the new circuits you're running (based on your code cycle).

For the main > sub cable, you can either use 6/3 NM cable (it includes a ground in it), or use a piece of PVC conduit between the panels and use three 6ga and one 10ga (ground) THHN wires. The NM cable is probably a few dollars cheaper, but the conduit might look cleaner - if that's important.
 
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Old 12-19-18, 12:50 PM
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Thanks for the clarification on the breaker. I have read that for home projects, It is acceptable to color code the individual wires with tape<?> In my application conduit would definitely look better.
 
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Old 12-19-18, 01:37 PM
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6/3 NM is rated at 55 amps. Heard of inspectors who won't allow it on a sub panel feed without a load calc.
 
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Old 12-19-18, 01:58 PM
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Per code you cannot recolor wires smaller than #4, however inspectors are often flexible on this point. You can never recode a green/ground.
 
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Old 12-19-18, 06:44 PM
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I would like to finish my basement so I am going to have to add a sub panel.

Most of the answers to your questions are just guesses till you can tell us what version of the NEC your city/town/county/state is on. Your very first step in planning is to consult the AHJ's office and ask about what codes you need to follow.
 
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Old 12-20-18, 10:28 AM
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My community, Cobb County, GA, is using the 2014 NEC.
 
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