Number of wires under one neutral bus bar terminal screw?
 

I was looking at our main panel today (residential, 100A service) with the cover removed. I noticed that in a couple of places, more than one neutral or ground is terminated under a single terminal screw on the neutral bus bar. Is this kosher? I don't know if there's a "one terminal, one wire" type rule regarding the neutral/ground bus bars.

For neutrals, it's one wire per screw. For grounds it may be 1,2,or 3 depending on the panel manufacturer. There should be a label either inside the panel or on the door that will tell you how many are allowed on the ground.

Thanks House, I'll look that up!

How did they use all the terminals up? They usually have enough for full capactity of the "skinny" breakers...

I put a new breaker panel in at at our house last weekend and I had to double encumber a few of the lugs because there simply wasn't enough slack in the wires to reach the next lug down. I thought it made more sense than making a splice inside of the panel.

Better to put a splice than chance a loose neutral due to more than one wire under a screw. There is no restriction to wirenutting two wires together inside a panel as long as there is enough space to do so. Most modern panels have that space.

Househelper, thanks for the info. I'll wirenut them asap.

This might resolve my first issue. I was checking to see if there's space to swap out the bedroom breakers for AFCI breakers, and to swap two other breakers for a SSP. I know the pigtails for the AFCIs and the SSP /must/ be as short as possible. So, I could if necessary splice a few other lines together to make room? Or is it better to get a longer length neutral bus bar and install it?

You do NOT want to be combining several neutrals under one wire nut with a pigtail to the buss: you risk overloading the pigtail. And most neutral bars are not replaceable.
For each AFCI breaker you add, you will be removing a neutral from the bus (it will now go to the breaker). If the breaker pigtail won't reach the now open hole, just add a short length of white wire to the pigtail to extend it.

Right, what I meant was that if there is a ground wire in a spot I need on the neutral bus, I could move that ground wire into a shared spot with another ground wire. Assuming my particular panel allows more than one wire under a screw in the neutral bus, that is. The neutral wire coming from the AFCI breaker would not share a hole. The idea being that I could move a ground wire to another spot if doing so would allow the neutral wire from the SSP to be take the shortest path possible.

Well when you put it that way, that is a good plan as long as this is a main panel (you said it was) and the neutral and ground buses are the same.

Would a licensed electrician be able to install a longer neutral bus bar if the existing one is already at safe capacity?

Yes, but I think adding a ground bar and moving the grounds to it would be easier and cheaper. The end result (more room on the neutral bar) would be the same.