Elecraft KPA500 Owner's Manual - Manual (Page 7)

7
 Replace the fuse block so that the correct mains voltage appears in the window in the cover. The
orientation of the fuse holder sets the proper connections to the power transformer for each mains
voltage range. When replacing the fuse block in the holder squeeze the fuses against the spring
contact so they will slide into the holder.
 Be sure the fuse block is fully seated in the holder as shown below before trying to close the door.
You may feel a lot of resistance just before it is fully seated as the fuses reach the contacts inside the
holder. That is normal.