Dealing with old wires?

I am going to split a circuit at an existing junction box. Can I just wirenut the old feed and leave it in the junction box?
The wiring is a real rats nest and there is no way telling where the feed wires come from, or I would certainly pull them out. (Though I suppose adding more wires will only make it worse...)
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When I re-wire old wiring, I remove all the old wiring and install all new wiring, junction boxes, etc. Especially if the old wiring is in bad condition (not safe) and the boxes are outdated or rusted.
I sleep better knowing all that old stuff is gone. But doing this requires ripping out walls and making a big mess. But then if ripping out walls, you can add more outlets, computer wiring, TV wiring, etc.
If just adding a new circuit and not doing a major re-wiring job, then I would examine the old wiring to be sure it is safe. If the insulation is cracking or falls to pieces when you bend the wire, then I would do whatever it takes to remove the old wire.
Also you should not have a "rats nest" in a junction box. This is called "box fill". The junction box should be large enough to hold all the wires. If there will be too many wires in the junction box, don't add any more. Install another junction box near it or install a larger junction box.
Box fill table... http://www.geocities.com/Colosseum/Bleachers/4589/Box-Fill.htm
"Wade Lippman" wrote in message

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