Robert Green wrote:
Bobby That last idea is a problem right from the start. The reason that the electric code specifically forbids connecting two neutral conductors under one terminal is that the two circuits will be loaded and unloaded in a random way during normal use. Each of the conductors will then expand and contract at different times causing the connection to the more lightly loaded of the two wires to be looser than the connector is designed to be and inducing heating in that connection beyond it's design limits. That leads to connection creep which gradually makes the connection less and less firm. Eventually arcing occurs and the neutral goes open leaving a circuit that appears to be dead energized from the breaker all the way back to the open neutral connection inside the panel. As one example of the danger to persons the screw shell of Edison based screw in light bulbs would be energized at 120 volts to ground. Someone thinks the bulb is burned out and tries to change it. If their finger comes in contact with the screw shell while they are unscrewing the bulb they get a shock. Even if there is no path to ground through their body their startle reaction alone could throw them off of a ladder or cause them to fall. If they are also in contact with some grounded conductive surface such as the metal surface of an installed lighting fixture they could receive a fatal shock. SquareD makes an isolated ground buss bar that is designed to be added to a panel were isolated grounds need to pass through a panel without being connected to other Equipment Grounding Conductors (EGC) in that panel. Installing one of those buss bars is a perfectly safe way to add additional neutral terminations to any panel No matter what the panel is being used for. It would be a technical violation of the panels listing and the listing of the isolated grounding buss bar but it would not in fact be unsafe as long as there is plenty of room in the existing cabinet to install the buss bar and the room to bend the additional conductors to each terminal. The additional buss bar would be connected to the the original buss bar by a copper conductor at least as large as the main bonding jumper called for in 250.28 Main Bonding Jumper. (D) Size.
250.28 Main Bonding Jumper. For a grounded system, an unspliced main bonding jumper shall be used to connect the equipment grounding conductor(s) and the service-disconnect enclosure to the grounded conductor of the system within the enclosure for each service disconnect. (D) Size. The main bonding jumper shall not be smaller than the sizes shown in Table 250.66 for grounding electrode conductors.If your panel is two hundred amps or smaller then that wire need be no larger than number four copper. IF AND ONLY IF YOUR PANEL IS ALSO THE SERVICE DISCONNECTING MEANS FOR YOUR HOME you could just install a supplemental Grounding buss as others have already suggested. Since the Equipment Grounding Conductors and the Grounded Current Carrying Conductors; by which read neutrals; are bonded to each other and to the cabinet you can use the supplemental EGC buss bar in the same way you use the neutral buss bar. In order to avoid having neutral current traveling on the bonding connections through the steel of the panel's cabinet you just add a main bonding jumper between the two buss bars so that current from any neutrals you terminate on the extra buss bar will have a low impedance pathway back to the utility neutral and thence back to it's source in the utilities transformer secondary winding.
-- Tom Horne