Wiring a Subpanel


Old 03-18-07, 12:33 PM
Thread Starter
Join Date: Jan 2007
Posts: 10
Wiring a Subpanel

I am planning to set-up a sub-panel to handle new circuiits on the second floor of an older home. My current thinking:

1 To the sub-panel run 6/3 approximately 50 feet from a newly wired breaker box with 100 amp service, protected with a double-pole 50 or 60 amp breaker.

2. From the sub-panel have 4 AFCI-protected circuits to the bedrooms @ 15 amps each.

3. From the subpanel have 1 GFCI-protected 15 amp circuit run to the bathroom.

4. From the subpanel have 1 circuit power lights in a small attic protected with a regular 15 amp breaker.

5. Circuits are all wired with 12/2.

Am I on track?

Am I overloading the 6/3 and subpanel with 6 15 amp circuits?

As I understand the rating for 6/3 I gather I should probably use a 50 amp breaker rather than 60, yes?

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Old 03-18-07, 02:06 PM
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
If you are using 12/2 wire, why are you running 15 amp circuits?

The bathroom needs a 20 amp circuit (in the US).

The number of circuits on a panel has nothing to do with the total power of the panel. What is important is what those circuits serve.
Old 03-18-07, 04:20 PM
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Join Date: Oct 2002
Location: Wally World
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Bob is correct. You need to determine the load that will be served from the new subpanel before you can correctly size the panel itself, breaker, and feeders.
Old 03-18-07, 05:41 PM
Join Date: Sep 2000
Location: United States
Posts: 18,497
You may use either a 50-amp or 60-amp breaker to protect the 6/3. You're not even close to overloading it with six circuits. You could comfortably put in twice as much load as you listed.

As Bob said, use 20-amp breakers if you're going to use 12-gauge wire. It's required for the bathroom receptacle, and it'll provide more flexibility everywhere else.
Old 03-19-07, 04:28 PM
Thread Starter
Join Date: Jan 2007
Posts: 10

I appreciate your feedback.

The point is well taken about the bathroom line and I'll be sure to put in a 20 amp GFCI breaker.

So what will happen if I use 15 amp AFCI breakers to the bedrooms with 12/2 wire?

Here's the scoop on use: all bedrooms except one will have "moderate" need with a few lamps, clock radio, and overhead lights. One bedroom will be used as a shared work space: computer, sewing machine, iron, small hand tools (e.g., a Dremel tool, small model-maker's lathe, resistance soldering unit), obviously not all running at the same time, but actively used.

Will the 15 amp breakers protest by tripping "prematurely."

By the way, I've been checking in with this forum since I began the project in January and appreciate the insights I've gotten. Thanks for your help.
Old 03-19-07, 05:01 PM
Join Date: Apr 2006
Location: New Bern, NC
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Get a good book. Read and understand what it says. (trust me it is not that hard).

Last edited by John Nelson; 03-19-07 at 06:51 PM. Reason: offensive post
Old 03-19-07, 05:30 PM
Join Date: Aug 2004
Location: NA
Posts: 1,065
If this is a small bathroom and your going to serve the lights and receptacle with one 20 amp circuit consider instead of a gfci breaker using a gfci type duplex receptacle wired line only, then pass constant power on to the lights. This will allow the gfci to trip and not take out your lights and it will save you 20 bucks. It also allows reset at the bathroom... you don't have to go to the subpanel.

Nothing will happen if you use 15 amp breakers but would really be a waste of power....1800 watts vs. 2400 watts. My opinion... anywhere that you will plug in a vacuum sweeper or laundry iron should be 20 amps. These items often stretch a 15 amp circuit to its limits.

If you have a 20 amp circuit you could run one 20 amp afci branch circuit to the two bedrooms that arent the multi-task room. This will save you some money on afci breakers.

Serve the multi-task room with one 20 amp circuit.

Note: There are a few specific's on wiring the feeder to the subpanel, so you might want to ask when you get ready to do this project.

I'm wondering also if maybe you have already purchased the afci breakers and that is the reason for your wiring design. It would be a real odd installation to use 12 awg with 15 amp breakers, it really doesnt make sense so consider exchanging them for 20 amp afci.

Old 03-19-07, 06:52 PM
Join Date: Sep 2000
Location: United States
Posts: 18,497
As Roger says, nothing bad will happen if you use 15-amp breakers on a circuit wired with 12-gauge wire. Go ahead and do it if you want to. It's fine.

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