Mine came with an autotransformer but the machine wants 240-3ph so I left the transformer out. You only need it if you are coming off 460 or something else like that. The transformer has an overtemp sensor in it that connects to the machine. If you don't have that, you will need to short pin2 to pin1 on the P6 plug in the R6 receptacle on the input module (upper right inside cabinet behind the output module ). See attached pic, I am pointing at the shorting wire on my machine.