If you are having trouble with your heat bed cutting out, your polyswitch fuse on the arduino is oversensitive. You can buy a $5 part at radio shack to prevent your heat bed from cutting out ever again. http://www.radioshack.com/product/index.jsp?productId=20875286 The heat bed will still be control in the exact same way. Only the wiring changes. I soldered the connections to the relay switch but you can also use Butt Terminals (double sided crimps). You don't have to take your bed off for this fix. It's shown in the picture that way for clarity.