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Old 09-24-2018, 09:04 PM   #1
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Why two circuits on the same outlet?


I was doing some demo today, and had to get a dead end outlet out of the way. I was a little confused though, as it was wired with 12-3, with the red going to the top gold screw, the black to the bottom, and the tab in between was broken. Of course, I thought I had killed the circuit and got bit when I touched the red, so there are two breakers.


I know a bit about shared neutrals and tying breakers together etc. but I just don't get the reasoning behind this. (a licensed electrician will be wiring this so it's just to satisfy my curiosity.) This is a family room in a finished basement, not some workshop or something.
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Old 09-24-2018, 09:14 PM   #2
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Re: Why two circuits on the same outlet?


It provides a separate circuit for each half of the receptacle, so twice as much power is available total. This may have been intended for a specific piece of equipment, like an air conditioner. Current code requires the two breakers to have a handle tie, or the use of a double pole breaker.
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Old 09-24-2018, 09:14 PM   #3
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Re: Why two circuits on the same outlet?


Either a 'split receptacle' on a multwire branch circuit or half the receptacle is controlled by a switch. If you know for sure it is connected to two breakers, then it is the former, but unusual in a family room. For that setting, more likely the latter.


Split receptacles with a shared neutral allow breaker current - usually 15a - available at each port of the receptacle.
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Old 09-24-2018, 09:31 PM   #4
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Re: Why two circuits on the same outlet?


While the code at the time may not have required the two breakers to
be connected by a handle tie, or the use of a double pole breaker, it
wouldn't be a bad idea to upgrade it with one of the above.
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Old 09-24-2018, 10:00 PM   #5
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Re: Why two circuits on the same outlet?


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Originally Posted by Marson View Post
I was doing some demo today, and had to get a dead end outlet out of the way. I was a little confused though, as it was wired with 12-3, with the red going to the top gold screw, the black to the bottom, and the tab in between was broken. Of course, I thought I had killed the circuit and got bit when I touched the red, so there are two breakers.


I know a bit about shared neutrals and tying breakers together etc. but I just don't get the reasoning behind this. (a licensed electrician will be wiring this so it's just to satisfy my curiosity.) This is a family room in a finished basement, not some workshop or something.
The switch that controls the black half may just have been off, not conventional but a lot of residential work is done by underpaid beginners and hacks.........and even ignorant DIYers

First find the switch that turns half of that receptacle off and on (why am I so sure there is one? because it's a common arrangement)
There may not be two circuits at all, do you have a multimeter? set it to read volts and stick each probe in the hot sides of each receptacle, if it reads "1"(digital multimeters) it's at least the same phase, if it reads 220 or thereabouts then it's two phases and definitely on two breakers.
Find the circuit breaker that turns either half off, if both halves are off then' it's the same circuit. When you open the switchbox you might see a black wire coming off the switch and entering a cable with a black and a white and ground wire too, the black wire going to a wire nut that the other wire (feeding) to the switch comes out of.

A trade convention fact for you, when professionals wire things with 12-3 we use the black for line voltage (constant hot) and red for the switched wire (switch leg), you might notice that photocells and occupancy sensors often use this same convention.

Last edited by Sparkomatic; 09-24-2018 at 10:13 PM.
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Old 09-24-2018, 10:11 PM   #6
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Re: Why two circuits on the same outlet?


Quote:
Originally Posted by mpoulton View Post
It provides a separate circuit for each half of the receptacle, so twice as much power is available total. This may have been intended for a specific piece of equipment, like an air conditioner. Current code requires the two breakers to have a handle tie, or the use of a double pole breaker.
most likely for a lamp in a family room, more likely the same circuit.
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Old 09-25-2018, 06:25 AM   #7
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Re: Why two circuits on the same outlet?


There are two breakers, not switched. I guess someone thought overbuilding was a good idea.
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