We are working on a project where there will be a portable generator brought to a facility in the event of a power failure. 480V 3-phase. We will have a fused disconnect located outside the building with cam lok connectors. Not knowing what portable generator will be used, I am trying to determine if a 3-pole or 4-pole transfer should be used. I am trying to find info on the portable generator (to see how the neutral is bonded at the genset), but they may have several and whichever one is available will be pulled up and plugged in. It is almost like there needs to be a sign someplace saying what type of generator can be used. How is this normally handled when you never know what unit will be plugged into it?
Since the important difference between an SDS and non-SDS connection is whether there is an earth-neutral bond at the generator (for non-SDS there cannot be, since that would be a second bonding point) I suggest the following:
If there is a ground-neutral bond internal to the supplied generator which you do not have the option of disconnecting, then you will want to switch the neutral, so that the ground-neutral bond used for the POCO service does not become a second bonding point. This will be an SDS installation.
That means that you will have to use a 4-pole transfer switch.
If there is not a ground-neutral bond at the supplied generator, you have the option of making one or else connecting the generator as a non-SDS.
In that case you do not want the neutral to be switched. The simplest way to do that with an installed 4-pole transfer switch is simply to connect a jumper across that pole of the switch.
So provide a convenient, well marked place to install that jumper, and document when it should or should not be installed.
You will also need to make sure that you provide for a 5 wire connection to the generator, not just 4. The EGC will never be switched though.
PS: If the generator is a 480V delta only, there will not be a neutral, while if it is a 480Y/277 there will be a neutral. It is my current understanding in the latter case that if your facility does not use the neutral for any loads, it still has to be brought to the the transfer switch and connected to any grounded conductor that may be present there.
In the first case, the grounding of the generator output has to be compatible with what your facility uses.