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I am wanting to convert a one gang to a two-gang wall outlet. I'd like some advice to make sure that I wire it correctly. I have full access to the box so that is not an issue. Attached is the back of the current outlet.

Do I connect all of the white wires together and run a pigtail off of them and do the same for the black wires? After installing the new second outlet, run a wire from the old to the new outlet?

I know how I stated the steps may be very simplified but hopefully, it allows you to see my thinking on the wiring. Please provide me insight of steps that need to change and/or adjusted. Thank you.
 

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Do I connect all of the white wires together and run a pigtail off of them and do the same for the black wires? After installing the new second outlet, run a wire from the old to the new outlet?
That will work but I would make two pigtails and run one to each receptacle.
I definitely would not use the back stab connections. They are a very common cause of loose connections.
 

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Discussion Starter #4
That will work but I would make two pigtails and run one to each receptacle.
I definitely would not use the back stab connections. They are a very common cause of loose connections.
Thank you for the suggestions. Just to be clear, putting together all of the black and white wires, I would end up with 5 black and five white wires together(with one of them being a pigtail for each)?

I agree with the backstabbing suggestion. This was done by the electrician when the house was built.

Just curious, with the white/black wires in my pictures, what are the three wires? Most of my other boxes I have looked at have two black and white wires and not 3. Just wondering. Thanks.
 

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You would need two pigtails for both hot and neutral, one for each receptacle.
Three cables would one power in from panel and two power out to other parts of the circuit.
 

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Discussion Starter #6
You would need two pigtails for both hot and neutral, one for each receptacle.
Three cables would one power in from panel and two power out to other parts of the circuit.
Just curious, is it possible to just use a short piece of wire and run it from the open screw off the old plug and run it to the new plug?
 

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Just curious, is it possible to just use a short piece of wire and run it from the open screw off the old plug and run it to the new plug?
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Yes, but it isn't the best way. Individual pigs are best workmanship. You replace a receptacle later if needed without dismounting both of them. Also it's not desirable to use a device for a junction... not a violation but just not good practice. I'd do it only in a pinch where the box was filled to capacity.

What is the depth of your new 2 gang box and will it have a mud ring installed? You may already be overfilled.
 

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Yes, but it isn't the best way. Individual pigs are best workmanship. You replace a receptacle later if needed without dismounting both of them. Also it's not desirable to use a device for a junction... not a violation but just not good practice. I'd do it only in a pinch where the box was filled to capacity.

What is the depth of your new 2 gang box and will it have a mud ring installed? You may already be overfilled.
The depth of the PVC two gang box is 2.5 inches and no mud ring, it is being installed on an exposed joist with no drywall.
 

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Your present box fill count is 10 #12 wires + 1 for all grounds + 4 for 2 switches (2 each per code) = 15 total fill count and a volume of approximately 34 in³. The box you are using has approximately 36.3 in³ (allowing for box thickness deduction) so you are OK for code compliance but it's close to max.

That's giving you the benefit of a doubt since the box may have the capacity marked at less than the calculations... depends on how it's constructed. Do you see any capacity marking on it?
 

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I cannot tell from the photos, but is half of that outlet controlled by a switch?
Perhaps that is the reason you have the third wire.

And as far as pig tailing....I would wire one outlet to pig tails and wire the second outlet parallel. (screw to screw). That will be one wire less under the wirenut. As it is you are going to have a hell of a time shoving all of those wires in the box.
Better yet, pick up two outlets which clamp on the wires instead of wind around the screws.
 

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Discussion Starter #11
Your present box fill count is 10 #12 wires + 1 for all grounds + 4 for 2 switches (2 each per code) = 15 total fill count and a volume of approximately 34 in³. The box you are using has approximately 36.3 in³ (allowing for box thickness deduction) so you are OK for code compliance but it's close to max.

That's giving you the benefit of a doubt since the box may have the capacity marked at less than the calculations... depends on how it's constructed. Do you see any capacity marking on it?
Is there a "better" sized box to use? I am just getting a "standard" box from a big box.
 

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You may need to grab one of these 3" deep ones to comply if you are using a box with cable ties built in since that reduces the capacity down to around 32 in³ or less. If that's true, your box is overfilled even if you don't pigtail the receptacles.
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3" deep pvc box
 

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Discussion Starter #13
I cannot tell from the photos, but is half of that outlet controlled by a switch?
Perhaps that is the reason you have the third wire.

And as far as pig tailing....I would wire one outlet to pig tails and wire the second outlet parallel. (screw to screw). That will be one wire less under the wirenut. As it is you are going to have a hell of a time shoving all of those wires in the box.
Better yet, pick up two outlets which clamp on the wires instead of wind around the screws.
No switch that I'm aware of, it's in an unfinished storage room. The breaker for the outlet is labeled, House GFI.

two outlets which clamp on?? I wasn't aware of this kind. Possible to show me an example of this kind? Appreciate the suggestion.
 

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Just curious, is it possible to just use a short piece of wire and run it from the open screw off the old plug and run it to the new plug?
Yes.


Better yet, pick up two outlets which clamp on the wires instead of wind around the screws.
I agree. These are called back wired receptacles (as opposed to back stabbed). These allow you to put two wires under one screw. Image of this type of screw terminal shown below. Available at big box stores.

Thank you for the suggestions. Just to be clear, putting together all of the black and white wires, I would end up with 5 black and five white wires together(with one of them being a pigtail for each)?
That is correct and you will have a difficult time getting 5 wires twisted and under one wire nut.

Your present box fill count is 10 #12 wires + 1 for all grounds + 4 for 2 switches (2 each per code) = 15 total fill count
I don't see the wire size stated anywhere. Present wire count is 9. Three black, three white, one ground and two for the device. The addition of another receptacle will up the wire count by two to 11. A conductor, no part of which leaves the box, is not counted.


Use of the back wired receptacle, putting two blacks under one screw and the third black and a pigtail to the second receptacle under the other screw is far easier and superior to trying to put five wires in one wire nut. Same thing for the white wires.
 

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