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Old 03-05-2019, 12:33 PM   #1
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10-3 cable on 100 amp load center?


Hi all. I am doing an attic master suite conversion and am going to power it off a load center (with no main breaker on that panel) in the attic run off my main panel in the basement. I'll have probably 6 circuits, all 120 volt, and a load calculation turned out to be 23 amps, so I'll use 10-3 wire. The load centers I'm seeing with enough spaces are typically 100 amp, but I'll use nowhere near 100 amps. If I use a 30 amp breaker in my main panel, I'm fine running 10-3 wire (probably 40 feet or so) to the 100 amp load center, correct? There's no 100 amp breaker in the load center, so I don't see why it should be an issue, but just wanted to verify. Thanks.
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Old 03-05-2019, 01:25 PM   #2
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Re: 10-3 cable on 100 amp load center?


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Hi all. I am doing an attic master suite conversion and am going to power it off a load center (with no main breaker on that panel) in the attic run off my main panel in the basement. I'll have probably 6 circuits, all 120 volt, and a load calculation turned out to be 23 amps, so I'll use 10-3 wire. The load centers I'm seeing with enough spaces are typically 100 amp, but I'll use nowhere near 100 amps. If I use a 30 amp breaker in my main panel, I'm fine running 10-3 wire (probably 40 feet or so) to the 100 amp load center, correct? There's no 100 amp breaker in the load center, so I don't see why it should be an issue, but just wanted to verify. Thanks.
Correct. The max rating of the load center is the max rating. You can feed it with whatever size circuit you want as long as it does not exceed 100 amps.
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Old 03-05-2019, 01:27 PM   #3
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Re: 10-3 cable on 100 amp load center?


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Originally Posted by eholmes77 View Post
I am doing an attic master suite conversion I'll have probably 6 circuits, all 120 volt,
...and a load calculation turned out to be 23 amps, so I'll use 10-3 wire.

If I use a 2P 30 amp breaker in my main panel, I'm fine running 10-3 wire (probably 40 feet or so) to the 100 amp load center, correct?
Electrically you're likely okay... but I suspect the code won't allow it.
but I also suspect the code won't allow an attic conversion either.
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Old 03-05-2019, 01:29 PM   #4
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Re: 10-3 cable on 100 amp load center?


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Electrically you're likely okay... but I suspect the code won't allow it.
but I also suspect the code won't allow an attic conversion either.


The project is all permitted and was designed by an engineer, so everything will have to be to code.


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Old 03-05-2019, 01:31 PM   #5
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Re: 10-3 cable on 100 amp load center?


You don't have to, but might be convenient to feed that sub with a breaker, so you can shut down that sub if you want to, rather than run to the main.
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Old 03-05-2019, 01:33 PM   #6
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Re: 10-3 cable on 100 amp load center?


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You don't have to, but might be convenient to feed that sub with a breaker, so you can shut down that sub if you want to, rather than run to the main.


I thought about that and may do it depending on cost, but itíll be rare that I have to shut that panel down.


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Old 03-05-2019, 01:37 PM   #7
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Re: 10-3 cable on 100 amp load center?


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You don't have to, but might be convenient to feed that sub with a breaker, so you can shut down that sub if you want to, rather than run to the main.


I also donít want to have to feed a 100 amp breaker panel with big wire, both due to expense and the fact itís hard to run that stuff.


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Old 03-05-2019, 02:22 PM   #8
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Re: 10-3 cable on 100 amp load center?


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I also donít want to have to feed a 100 amp breaker panel with big wire, both due to expense and the fact itís hard to run that stuff.


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You don't have to.... you can use a 30
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Old 03-05-2019, 02:28 PM   #9
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Re: 10-3 cable on 100 amp load center?


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You don't have to.... you can use a 30


Gotcha. Thanks.


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Old 03-05-2019, 03:25 PM   #10
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Re: 10-3 cable on 100 amp load center?


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You don't have to.... you can use a 30


I canít run 10-2 wire to a 100 amp sub panel with 100 amp breaker, right? Or can I since the 30amp breaker in the main panel would trip if it gets overloaded?


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Old 03-05-2019, 03:41 PM   #11
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Re: 10-3 cable on 100 amp load center?


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I canít run 10-2 wire to a 100 amp sub panel with 100 amp breaker, right? Or can I since the 30amp breaker in the main panel would trip if it gets overloaded?


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You could but the panel would only have 120 and half the spaces would be unusable.

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Old 03-05-2019, 03:53 PM   #12
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Re: 10-3 cable on 100 amp load center?


30 amp 2 pole in the main, 10/3 w/grnd to subpanel. If you buy a main breaker panel, the 100 amp breaker is OK as it is just acting as a disconnect. Over current is the 30 amp in main panel.
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Old 03-05-2019, 06:12 PM   #13
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Re: 10-3 cable on 100 amp load center?


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30 amp 2 pole in the main, 10/3 w/grnd to subpanel. If you buy a main breaker panel, the 100 amp breaker is OK as it is just acting as a disconnect. Over current is the 30 amp in main panel.


I only need 120, but if I only hook one hot wire to one of the two lugs I will lose half the slots, right? Do they even make 120 volt load centers? Or can I jump the two lugs together with a wire so all the slots work? I need to meet code.


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Old 03-05-2019, 06:38 PM   #14
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Re: 10-3 cable on 100 amp load center?


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I only need 120, but if I only hook one hot wire to one of the two lugs I will lose half the slots, right? Do they even make 120 volt load centers? Or can I jump the two lugs together with a wire so all the slots work? I need to meet code.


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There are compliant ways to do it but the connectors will cost note than the 10-3 cable. And the inspector may look at it doubtfully.

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Old 03-05-2019, 06:45 PM   #15
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Re: 10-3 cable on 100 amp load center?


I would like to suggest that instead of referring to the panels by their max Amperage capacity that you think of them as I do. Main panel and Sub-Panels.

Even though the "Main Panel" has a 100 amp main breaker in it, thus limiting it max amperage, the panel itself could be anywhere from 100 Amp to 200 Amp or more.

You need to buy your Sub Panel based on the number of circuits you want it to hold, while ensuring the breaker controlling it is rated under the max amperage of the Sub and Main Panels.

If your main panel is full, you can alway free up a couple of adjoining spaces by moving the circuits from the main to the sub-panel. Also, and I believe this is correct, you are not limited by the number of sub-panels you can have.

I have a sub-panel for my hot-tub. I needed 50 amp but it actually was cheaper to buy the better quality 60 amp. The 60 amp also allows me to add a couple of circuits for outdoor wiring.

I have another panel in my basement which allows me to clean up the wiring my idiot of a prior owner did. (Can you say splices just twisted together with electrical tape and no junction box?)
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