Does the NEC say that you can only connect one set of wires per device in a box? The reason I ask is because I was working with an electrician and he had me pigtail every connection where we fed multiple outlets with one feed. Here's what I don't understand about that. If I am running a feed to a pigtail which is made using either wire nuts, or those push in three hole connectors, how is that a more "failsafe" connection than using the screws on the sides (top and bottom) of the outlet? I have seen times where a wirenut has fallen off of a connection (I assume from vibrations caused from walking or jumping around) and the push in connectors, although very quick to use, seem to work similar to the push in feature in the back of outlets which I was told from a teacher never to use because they only make contact with a small area of the conductor and that isn't as solid of a connection. Would someone clarify this for for me? I wired my house using the top and bottom of the outlet and just pigtailing the ground, but now I am thinking I might have to go through and add pigtails to the hot and neutral too.
Thanks