Basic Types of Electrical Wire
There are many types of electrical wire for each possible condition the wire will be placed in. Some for indoor use only and some that can be buried directly in the earth and of course there’s a higher cost for the added options.
THHN wire is the single copper hook up wire used alone and inside other electrical cables in the industry. THHN stands for Thermoplastic High Heat resistant Nylon jacket the the dual rated THHN/THWN wire adds in “Water Resistant”.
Romex® is an indoor-only cable manufactured with THHN wires and a thin PVC jacket made solely for the ease of installation. Otherwise, electrical contractors must run each THHN wire by itself or tape them together and attempt to run them as one. Romex® cables were made to be cheaper because when adding all the bells and whistles you’ll end up with a much more expensive cable.
MC cable was manufactured because contractors wanted to run Romex® cable outdoors and in conduit but couldn’t because the jacket was thin and the bare copper ground wire could be damaged. So Southwire decided to change the jacket slightly and also make the ground wire insulated, using a THHN wire instead of bare copper.
MC cable can now be used outdoors and in conduit. There is also a PVC jacketed MC cable which keeps it watertight for direct burial in the ground. Just ask for MC cable with PVC jacket.
UFB cable stands for Underground Feeder with ground. This cable comes in the standard circuit sizes of 14 AWG through 6 AWG and come in 2 or 3 conductors plus a ground wire. The ground is bare copper but the UF-B jacket is very strong and can handle the underground abuse.
Now you know exactly which cable to use for each location you’re running it. The only thing left to do is call your electrician and ask them which size you need for the amount of power.