Found an interesting setup in an older home. Two separate circuits feed up into a junction box, with two separate neutrals, ground. From there they split into a 10/4 arrangement with one neutral feeding the two hots, and into a 10/3 single circuit for lighting. Later down the line the 10/4 has the second circuit on outlets and the first circuit on more lighting. Does this work? What problems might happen down the line? Should it be re-done? They are on two different phases.

I am having a little difficulty getting a picture in my mind how this is wired based on your explanation, but something sure does not sound correct.

Any chance you can make a sketch and post it as an image?

Sounds like any one of the two neutrals can be overloaded.

This may be nothing more than a branch circuit that has been divided to service two areas.

For example one run may be the feed for the receptacles in a room while the other is for the lights in the same room.

Yes a drawing or schematic would be terrific but if you have to manually map the circuit, you can do this by plugging in a radio and then turn off breakers one at a time until you find the correct circuit. Then see what size is on the breaker.

Where is the feed to the junction box?

What is the size of the breaker?

http://img521.imageshack.us/img521/2899/screenshot20101106at305.png

Sorry for the crude drawing... I just did it in word real quick.

Excellent job, thank you.

The neutral of the upper two wire plus ground circuit needs to be separated so that the feeder white only connects to the white continuing that upper circuit.

The black jumper from the upper circuit to the black on the lower circuit needs to be disconnected also, leaving the upper two wire plus ground completely separated.

This leaves the two whites joined together at the lower circuit, and the black of the lower circuit with no feed.

The 3 wire plus ground needs to be extended back to the panelboard.

Good catch, unfortunately I think you need to check other boxes that may be similar, as someone clearly did not understand circuitry.