Two Circuits Sharing Junction Box
I currently have a junction box inside a wall where a switched line separates to drive a light and a fan. (1 switch turns on the light and fan in a bath) I am pulling a new line to drive the fan but would like to attach inside the junction box as pulling the new wire all the way to the fan is problematic. Is this a bad idea? I wasn't sure if there are code restrictions on two circuits sharing a junction box.