No Romex® cables of any size should not ever see the light of day for any reason. There are many reasons that this cable cannot be used outside even if it’s a short run or a small piece of the cable. It was engineered and manufactured to be used indoors and has been priced accordingly. The low price makes it attractive compared to an outdoor electrical cable but it will only make things more complicated down the road.
Romex® 8/2 is one of the larger sizes of Romex® cable compared to the circuit sizes between 14 and 10 AWG. Just because it’s larger doesn’t make it any more protective from the outdoor weather conditions. All it means is that the copper is larger and can conduct more electricity. In order for it to remain a low cost item the engineering, testing and approving process needs to be kept to a minimum.
The main reason that a Romex® cable needs to stay indoors is due to the bare copper ground wire inside the jacket. The jacket is manufactured to simply bundle the wires together in order to quicken the installation process for the contractor. It hasn’t been through any testing processes for outdoor use because it would be a waste of money when it’s advertised as an indoor cable only.
The two THHN wires are actually approved to be used outdoor individually so you could buy 3 separate THHN wires to run instead of having the cable with a bare copper ground wire. The thin PVC jacket will be penetrated by water, gasses, oils, solvents and many other types of chemicals which would complicate the connection because of the bare copper ground wire. If the ground wire had green insulation it would be approved for outdoor use but it doesn’t.
Once the cable gets as large as 8 AWG the THHN wires become stranded copper instead of a solid strand. It adds a slight amount of flexibility but it is still far from a “flexible cable”. Once the copper strand gets as large as 8 AWG it becomes harder for installers to deal with even though they like the cable to be nice and stiff for snaking purposes.
There are many more types of 8 AWG 2 conductor cables that can be used outdoors or even directly underground. Speak to your supplier about the cheapest way to get an electrical cable with all of the approvals that are needed to meet the NEC code.
WesBell Electronics is a wire and cable distributor that stocks Romex ® and all types of hook up wire. Romex® 8 2 wire is a common item that we have in our inventory in 2 or 3 conductor with an additional ground wire included.