Differences Between THHN UF-B Cable and Service Entrance Cable

Electric cable

There are all different types of electrical wiring for different applications. We’ll break it down piece by piece. Common terms for electrical copper wire would be building wire, THHN/THWN, Romex wire, UF-B wire, and type SE (service entrance wire). All of these copper wires and cables have their own advantages and disadvantages depending on the individual wiring application. Each of them will be described in more detail below. Building Wire is just another broad term that is used in the same way as electrical cable. Since it is mainly used in the building/construction field, it has become a popular term.

THHN/THWN wire

THHN/THWN-2 Copper Power Cable is the most basic form of power cable used in homes, buildings, and control circuits not exceeding 600 volts. All of our THHN electrical wire is dual rated with THWN-2 because THWN is so popular that South Wire (the largest manufacturer of electrical wire in the US) decided to put both ratings on all of their THHN building wire. It is comprised of soft drawn bare copper strands, covered with a PVC (polyvinyl chloride) insulation and a nylon jacket for easy installation in cable tray. Those from 18 awg to 10 awg come in solid or stranded copper. Stranded cable is more flexible, while solid cable is easier to get through difficult areas.

More specifically, THHN wire runs through homes and buildings to light switches, electrical outlets, and lighting fixtures. THHN’s smaller gauges are commonly sold in 500′ spools which many vendors do not cut. WesBell Electronics will cut reels #18 – #10 at 100′ and will cut #8 – 1000 mcm per foot! That’s right, you can buy 1 foot of cable if you need to! WesBell understands that every application is different and we don’t want contractors to have to suffer from excess copper wire. By adding that to the resale price, it could cost you the job! Buy exact lengths, get exact quotes, and don’t have extra copper at the end! Copper is back up to over $2.00/lb so every foot of wire counts!

Romex Wire

Romex copper electrical wires and cables are made of multiple THHN/THWN wires (conductors). Example; Romex 12/2 has 2 THHN wires and an uninsulated bare ground wire covered with an overall PVC sheath. This way, electrical contractors only have to install one wire in bulk instead of running 3 separate wires or installing each wire individually. Romex cable is ONLY used for indoor applications. It is NOT protected against moisture, gas or solvents. It should NOT be used outdoors, even if it is in a cable tray.

UF-B cable

UF-B (Underground Feeder) Copper Electrical Wires and Cables are a slight improvement on Romex cabling. It has the same concept as the THHN conductors wrapped in a jacket except that it is a more complex jacket. The advantage of UF-B cable is that it can go outdoors and even directly underground. There is no need for conduit or cable tray and the price difference is not that significant. If you need the cable to go outdoors, make sure you get UF-B instead of Romex because it’s not worth the trouble to replace the Romex in the future with something about 10-15% more expensive.

Type SE Service Entrance Cable

You will sometimes see an “R” (SER) or a “U” (SEU) after Type SE. The R stands for round (most common) and the U stands for flat. Southwire Type SE electrical cable, service entrance cable is mainly used to carry power from the service drop to the meter base and from the meter base to the distribution panel board; however, the cable can be used in all applications where Type SE cable is permitted. SER can be used in wet or dry places at temperatures not exceeding 90°C. The nominal voltage is 600 volts. Southwire Type SE cable is constructed with Type XHHW-2 sunlight resistant conductors or Type THHN/THWN conductors.

Copper conductors are annealed (soft) copper. The cable assembly plus reinforcing tape are coated with gray sunlight resistant polyvinyl chloride (PVC). Available as 1-conductor concentric ground, 2-conductor round or concentric ground, or 3-conductor bare ground. The SE cable is sheathed with gray sunlight resistant polyvinyl chloride (PVC).