..How big is the "j-box"..? you have to watch how many wires you're cramming into that box..and if you are running another circuit in there..don't splice all your neutrals together..egc's can all be spliced together,..Common handle tie on the breaker,..?..no.Only when you have 2 phases on the same yolk or device..ie;a receptacle with the hot side bridging taken off...that you have to use a 2-pole breaker...Different phases..? it won't matter as the neutrals of each circuit should be separated anyway!! Hope this helps ya.. AR
.."if it ain't fixed,don't break it...call a Licensed Electrician"