Pigtail electrical wires to install new electrical outlet?

Is the "Tab" broken off on one side of the receptacle?

I found your description a little hard to track, but you gave enough clues to make me think you missed a detail. Having the white connected in a wire connector with the blacks is wrong unless feeding a switch. I think one half of that duplex is or was controlled by a switch. If I'm right this is what you should have if wired right. (But first a disclaimer, any good electrician would find the other end of the white connected with the blacks and confirm it is connect to a switch, this would require a continuity tester like this, http://www.amazon.com/gp/product/B00064CH6A/ref=as... , to confirm switching, you can get one for under $10 at your local big box hardware store.)

To control 1/2 the receptacle, with the other half hot:

1) The cable with the white attached to the blacks should go to a switch, the black should attach to a gold screw on the small blade side of the receptacle with the gold tab broke off.

2) The white from the same cable should attach in a wire connector to all the other blacks including your new one, and a pigtailed piece of wire to the other gold screw side of the receptacle.

3) The rest of the whites need to go together with a pigtailed piece going to a white screw on the tall blade side of the receptacle. If the tab has been broken on that side then a pigtail needs to go to both top and bottom white screws.

4) All the bare grounds need to be connected together and pigtailed to the receptacle.

Basically, the short wire (black) (white) that run from their respective pigtails connect the outlet to the wires. The green (with one long) is specifically for grounding. That MUST be there to keep you safe.

When adding in a new line (two wire system with ground) you can probably just hook onto the second set of screws on the outlet. Just keep black with black and white with white and ground with ground.

It's important to note that the plug is polarized. That means the hot is ALWAYS on one side of the plug and the neutral on the other. The brass screws are for the HOT and the silver screws are for the NEUTRAL (((((CORRECTED INFORMATION))))). Another way to tell which is which is by looking at the blade slots. The hot blade slot is always shorter than the neutral. WHY? Because you want to be able to get power away from the plug better than you can get it in. The ground is also there to help in the event of a short circuit. Don't ignore it. It's important for your safety.

Hope this helps.

'av'a g'day mate.

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ADDITIONAL: "Not as think" is right, the brass screw IS the hot and not the way I had it. I WAS WRONG. Sorry, it was an oversight. Thanks for clarifying my error. I'm not a proud man, more like humble.

But yes, the brass IS the hot. Sorry for any confusion I may have created. I'll have to take my drawing down so no one else gets confused.

Pigtail Electrical Outlet

the dog up there has the polarity backwards, the hot goes to the brass screws and the neutral to the silver (sorry to call you out, but safety first)

Duplex receptacles have (4) screws for termination points along with a green screw dedicated for ground. One side of the receptacle has (2) brass screws and the other side has (2) silver screws. The hot side of the circuit (black wire) should be wired to the brass screws while the neutral side of the circuit (white wire) should be wired to the silver screws.

It would seem that is not the end of your circuit. I can't tell from your description how best to proceed, unfortunately. Have someone experienced come take a look at it.