MC cable and UF-B Cable are manufactured for different applications but can be interchanged in some situations without any problems. The reason they can be interchanged in some applications is the fact that they both have the approvals and protection to be used in outdoor situations.

MC cable is a slight upgrade to the indoor Romex cable. It has all THHN wire conductors along with a green THHN ground wire which allows the cable to be used outdoors and in conduit. It does not have the protection to be used directly underground unless there is an additional PVC jacket over the armor.

MC cable with PVC is an underground cable that comes in copper or aluminum. The PVC jacket over the aluminum armor keeps the cable moisture tight and allows it to be directly buried in the earth.

UFB cable is also an underground cable, so why make both? Well UFB cable comes with a bare copper ground wire, unlike the MC cable and only offers awg sizes up to a UFB 6/3. MC cable comes as large as MCM sizes with multi conductors and a ground wire. UFB is sometimes used outdoors and in conduit (like MC cable) because it has the ability, but if you're buying new you should go with an MC cable without PVC because it's cheaper.

Take a look at the links and descriptions to the right. It shows the order and simplicity of electrical wire based on the protection needed in the most cost effective way.