5 Circuit protection comes in many flavors. From the old-school glass fuses to modern ATO blade fuses, fusible links, and more. It’s imperative that for any add-on circuits you plan that they be protected. Usually the installation instructions will tell you what the fuse size needs to be, but if it isn’t stated, you can usually determine what is needed with a little basic math. See our sidebar on Tony Candela’s book where you can learn all about Ohm’s Law and more to determine proper fuse protection.