I recently saw a sub-panel with 40 breakers and two bus bars on each side of the breakers with about 35 screws (taps) on each side. The neutral wires (white) were all attached in to the bus bar on the left side of the breakers and the ground wires (uninsulated copper conductors) were attached on the right side bus. Three neutral (white) and three ground wires going to each screw and a few screws on each bus bar (both the left and right) were unused. The question is should only one neutral wire to attached to one screw on the bus bar to avoid potentially overloading the circuits or is it OK to put multiple wires on a single screw. I have been told that only neutral wires should go on the left and right side bus bars and the ground wires should be attached to a bus bar located on the back side of the panel box. Any help to clarify this will be appreciated.
If you can avoid doubling up, you should. But it won't overload the circuit. Most of the older switchboards I work on have the earths soldered together behind the switchboard, but all the circuit breaker enclosures I buy have neutral and earth links inside the enclosure, so it can be done either way. What Form what I know wrote is a bit misleading. Every single phase appliance that is using power has the same load going through the neutral as the active(Unless there is earth leakage). It is only on three phase appliances (i.e a three phase motor) that there can be no load in the neutral. For the mains of a house, it is very very unlikely to have a perfectly balanced load where no current is traveling back through the neutral mains. If the neutrals weren't earthed and you lost the neutral from the powerline, You would have a lot new appliances to buy, Because the three phases create their own (floating)neutral and you get strange voltages everywhere and would blow stuff up.(But only if you have three phase)
Slow down with the thought of replacing wires because of that. As long as the entire system is wired to NEC specs (hot, neutral and ground) there shouldn't be a problem with the wiring. If you find a neutral that has no connectivity to ground, then there is an interruption in these wires, most likely in the grounding wire, otherwise you wouldn't have any power coming out of this circuit at all. Usually the neutral and ground are tied together in the breaker box (in some Canadian provinces and north eastern states it might be different, they're going for a separate neutral and ground), this is where you have to look for. Check for loose connections or corrosion, this may be the answer to the problem.
theoretically there is no load on the ground wires or the neutral wires when a load is present on the neutral wires it is usually due to an unbalanced load the ground wires are to be on a bus bar that is NOT isolated from the panel so that it can carry any short from the panel to ground and the neutral bus bar is isolated from the panel so that it is attached to the neutral going back to the service. it would be better if each wire landed on a terminal but you could wire several neutrals then just have one reach the bus bar so long as the neutral wires are returns from breakers that are in phase. where the bus bars are located makes no difference so long as they are identifiable having a bus bar on the back of a panel seems impractical since it may be inaccessible.
