I recently completed a design for a fire station. In that design I had an emergency panel fed from a generator. I used an automatic 3-pole transfer switch and bonded the system as a non-separately derived system(solidly connected neutrals, no bonding jumper or electrode at the generator). The client has now requested I make provisions so a portable generator can be brought in and back up the entire electrical system in addition to the on site generator. My initial reaction is to provide a manual 3-pole transfer switch and bond the system as a non-separately dervied system. Doing this leaves the neutrals of the 2-generator systems solidly connected, the only neutral to ground bonding jumper in the whole system is at the main service. Does any one know if this is an issue? Should I use a 4-pole transfer switch at the on site generator, to isolate the 2 generator systems all together?