First check the label on the portable classroom. If it has a label it may also have instructions on the type of supply.
Does it have a label on the side saying "connect 120 / 240 volt single phase four wire feeder here". ?
When in doubt read the instructions or check with the manufacturer. I have not seen any portable classrooms that did not have a service located outside and a four wire feeder to the panel in the unit.
Alan --Inspector.
