According to the Feed the Beast Wiki article, Electrical Engines take 6 EU/t and output 2 MJ/t. Since I'm powering a forestry machine outside of my main power station, I wanted to use efficient cabling to transfer power to the engines. So I thought I'd use Tin Cable because it's much cheaper than Glass Fibre Cable. However, Tin Cable can only withstand 5 EU/t; no problem, just upgrade my Electrical Engines with a Small Curcuit Board containing an Iron Electron Tube, which reduces the power required by 1 EU/t.
So I built two Electric Engines, and gave them both a Small Curcuit Board upgrade with Iron Electron Tube. I connected them to a Logger and Arboretum, and then wired up some Tin Cable from an LV transformer pulling off of my main power storage. As soon as I placed the last cable, the whole cable exploded and disappeared! Isn't the EU/t based on what is being requested on the far end, which should be 5 EU/t? Why can't I use Tin Cable in this situation?