Differences Between THHN Wire UF-B and Service Entrance Cable

Electrical Wire

There is all different types of electrical wiring for different applications. We will break it down for you piece by piece. Most common terms for copper electrical wire would be building wire, THHN /THWN, Romex wire, UF-B Cable and Type SE (service entrance cable). All of these copper wires and cables have their own advantages and disadvantages based on the individual wiring application. Each one will be described in more detail below. Building Wire is just another broad term used in the same way as electrical wire. Since it’s used mostly in the building / construction field its become a popular term.


THHN / THWN-2 copper electrical wire is the most basic form of electrical wire which is used in houses, buildings and control circuits not exceeding 600 Volts. All of our THHN electrical wire is dual rated with THWN-2 because the THWN is so popular that South Wire (Largest Electrical wire manufacturer in the USA) decided to put both ratings on all their THHN building wire. It’s composed of soft drawn bare copper strands, covered with a PVC (Polyvinyl Chloride) insulation and a nylon coating for easy installation in cable tray. The 18 awg through 10 awg come in stranded or solid copper. The stranded wire is more flexible, while the solid wire is easier to run / snake through tough areas.

More specifically, THHN wire is run through houses and buildings to light switches, electrical outlets and light fixtures. The smaller gauge sizes of THHN is most commonly sold in 500′ spools which a lot of suppliers won’t cut. WesBell Electronics will cut the #18 – #10 to 100′ spools and cut the #8 – 1000 mcm per foot! That’s right, you can buy 1 foot of wire if needed! WesBell understands that every application is different and doesn’t want contractors to have to suffer excess copper wire. When adding that into the the resale price it could cost you the job! Buy exact lengths, get exact quotes and don’t have any extra copper at the end of it! Copper has jumped back up to over $2.00/lb, so every foot of wire counts!

Romex Wire

Romex copper electrical wires and cables are made up of multiple THHN / THWN wires (conductors). Example; Romex 12/2 is 2 THHN wires and a bare uninsulated ground wire covered with an overall PVC jacket. This way electrical contractors only have to run one bulk wire instead of either running 3 separate wires or individually running each wire. Romex wire is ONLY used for indoor applications. It has NO protection against moisture, gas or solvents. It should NOT be used outdoors even if it’s in cable tray.

UF-B Cable

UF-B (Underground Feeder) copper electrical wires and cables are a slight upgrade from Romex wiring. It has the same concept of THHN conductors wrapped with a jacket except it’s a more complex jacket. The bonus to UF-B Cable is that it can go outdoors and even directly underground. There’s no need for conduit or cable tray and the price difference isn’t that significant. If you need the cable to go outdoors at all make sure you get UF-B instead of Romex because it’s not worth the hassle of replacing the Romex down the road over something roughly 10-15% higher in cost.

Service Entrance Cable Type SE

Sometimes you will see an “R” (SER) or a “U” (SEU) after the Type SE. The R stands for round (more common) and the U stands for flat. Southwire Type SE electrical cable, service entrance cable is primarily used to convey power from the service drop to the meter base and from the meter base to the distribution panel board; however, the cable may be used in all applications where Type SE cable is permitted. SER may be used in wet or dry locations at temperatures not to exceed 90°C. Voltage rating is 600 volts. Southwire Type SE cable is constructed with sunlight resistant Type XHHW-2 conductors or Type THHN/THWN conductors.

Copper conductors are annealed (soft) copper. Cable assembly plus reinforcement tape are jacketed with sunlight resistant gray polyvinyl chloride (PVC). Available as 1 conductor with a concentric ground, 2 conductor with a round or concentric ground, or 3 conductor with a bare ground. SE cable is jacketed with gray sunlight resistant polyvinyl chloride (PVC).

Source by Chris G Bell