The right way to do this is to have the N/G bond at the transfer switch, so you run five wire (L/L/L/N/G) from each genset to the transfer switch, where you have a neutral bar, a ground bar, and a link between the two being the N/G bond, so all solidly connected together, and a three pole transfer switch. ...
That could meet the NEC rules as well but IMO there is no 'right way' only peoples preferred way. ...
Bob - You're right, of course. However, db's response points out an excellect design issue that gets important real quick.
With a bond in one gen only, there is no easy to disconnect (take completely off line) that gen, to pull electrical maintenance.. A system fault puts the tech at risk. And 4W transfer switches just aren't common. And, depending on the size of the gens, the transfer switch may well be two CBs in the Switchboard.
The following discussion is not concerned with the NEC, rather the best way to install for safety and maintenance. And it probably exceeds the NEC as well.
Tiger -
From your posts, you appear to have a pretty good handle on the issues - which is good, you will get this.
Most of my work is multiple generation, both isolated and parallel, mostly located off-grid. I highly recommend following db's design:
Assuming 3phase:
Wire each gen 5W to the transfer switch, solid neutral. If I could, I'd put the N-G bond in the main panel after the transfer switch.
Additionally, for safety in maintenance, install a neutral disconnect switch on each gen. It only has to be large enough to carry the design neutral current. If all you have are fused disconnects, slug the fuse slot - No Fuses In The Neutral. Lock this disconnect open as part of your LOTO when you are doing electrical maintenance.
If you are concerned with leaving it open when the maintenance is completed, wire one of the un-used poles onto the gen start circut. That way the gen won't run with out the switch being in the closed position. Aux contacts on disconnects are not common, and the disconnect will be a two or three pole - so there will be extras.
I don't know what you have for generation, so assuming you are 208V - 480V, 200A - 400A, the neutral disconnect will likely be in the 100A - 200A range. I'm sure someone will give you grief for using a 4/0 disconnect lug for a #14 control wire. Not to worry, there are several methods to fix this. The simplist is to unbolt the lugs and use crimp terminals on the control wires big enough to fit the lug mounting studs. If that is not available, I'm sure you will figure out a safe connection.
Good luck. Stay safe. Write back and let us know how the job comes out.
cf