a 480-120/240 50kva dry transformer, i am doing the bonding in the trans. do i ground the trans. frame with the 480 ground and remove the 120/240 strap to the frame. all raceways are pvc with on the 480 side i have 2 phases and a ground. also this trans is mounted on a portable plant with the 120/240 volt panel, the trans and panel are on the same steel frame. what is the proper grounding and bonding.
Leave the strap to the frame in place.
Bond the green wire from the 480 volt side and the green wire on the 120/240 side and the building steel and any metal water pipes in the vicinity served by the secondary to the enclosure. the strap will connect the equipment grounding system to the neutral connection of the transformer.
The objective here is to clear any ground faults by ensuring a low impedance path back through the equipment ground to the neutral connection at the transformer.
On the 480 volt side, the equipment grounding conductor needs to also be connected to the enclosure to create a low impedance path back to the 480 volt distribution center, then to the service and back to the utility transformer to clear any faults to the transformer enclosure.
We cannot clear any ground faults without a complete low impedance path through the equipment grounding system.
Make sure that the neutral on the secondary side is bonded to a grounding electrode system and to the EGCs for the loads. Many of the bonding straps in the transformer only bond the frame of the transformer to the case. Sometimes they bond the secondary neutral, but that is somewhat rare nowdays.