Service Entrance Cable (SE, SER, SEU, USE-2)

What it is

Type SE (service-entrance) cable is listed to UL 854 and installed under NEC Article 338. It comes in two main styles. SER is a round cable with insulated phase conductors, an insulated neutral and usually a bare grounding conductor. SEU is a flat or oval cable with two insulated conductors wrapped by a bare concentric conductor that serves as the neutral. USE-2 is underground service-entrance wire, usually sold as single conductors rated for wet locations and direct burial.

How to identify

Look at the cross-section. A round cable with four separate conductors (two black, one white or white-striped, one bare) under the jacket is SER. A flat cable with a layer of fine bare wires spiraled around two insulated conductors is SEU. Single conductors with heavy insulation printed "USE-2" are underground service-entrance wire. Size is printed as, for example, "2-2-2-4 AL SER," listing phase, phase, neutral and ground sizes.

Style comparison

Copper vs aluminum

Most SER and SEU sold today is aluminum, made from AA-8000 series alloy. Aluminum is lighter and costs less, but it needs a larger conductor than copper for the same circuit. Terminals must be marked for aluminum (AL or AL/CU). Clean the conductor and use antioxidant compound where the terminal maker calls for it. Conductor sizing comes from NEC 310 and the service and feeder articles, not from this sheet.

Key points

• On a feeder to a subpanel, the neutral and the equipment ground must be kept separate. SER provides both. SEU's bare concentric conductor cannot serve as both.
• USE-2 alone is not permitted for interior wiring unless it is also marked with a building-wire type such as RHW-2 or RHH. Many reels are dual or triple rated. Read the print.
• Sunlight resistance and support rules are in NEC Article 338 and the service articles 230.

Common mistakes

• Using SEU for a new subpanel feeder.
• Landing aluminum conductors on terminals not rated for aluminum.
• Pulling USE-2 single conductors inside a building when the print shows no building-wire rating.
• Ordering by "size" without stating copper or aluminum.

Governing standards: NEC Article 338; NEC Article 230 (services); NEC 310 (conductors); UL 854 (service-entrance cables).

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.