split-bus panel neutral

[mjmike]

Have a question on the neural for older split-bus panels. There is an older split-bus panel with one section being normal/emergency and the other being emergency only. The panel is 1-phase 120/240 with each bus 100A rated. The panel currently uses the conduit as ground, separate phase conductors to each bus, but uses a common neutral. The existing panel is going to be reconnected to a generator system with a new E-only and N/E panel. The phase conductors aren't an issue, nor is the ground, but can the single neutral go to a JB then split/tapped so it is connected to both the new E-only and N/E panel? Not sure if the existing split bus panel has separate neutral bars or a single neutral bar.

If this is done, the possibility exists that one new panel can be off and the other on and there could be neutral current going to the panel turned off.

 

[PetrosA]

If this panel contains your service disconnect(s), I think you'd have a problem, since you'd be required to bond both neutral bars to ground, unless you can have one panelboard with both a service rated bus/neutral and an SDS + neutral bus together. Strange thought. If it's a sub, you should already have a floating neutral bar, so adding a second one would be easy enough. This is a curious setup.

 

[JoeStillman]

You need a neutral to run in the raceways of both feeders. The neutral current needs to offset the unbalanced phase current in order to prevent inductive heating in the raceways.