Service-Entrance Cable

Service-entrance cable is the heavy jacketed cable family that brings power in: SE for above ground, USE for underground, with the letters after SE telling you the shape and conductor count. It exists so that services and large feeders can be run as a cable instead of conduit and individual conductors.

Why it matters on the job

Every residential service upgrade, subpanel feed, and range or dryer circuit is a chance to pick from this family, and the choices are not interchangeable. USE indoors is a fire-rating violation. SEU used where a separate equipment ground is needed is a grounding violation. The cable names encode exactly what each assembly can do; learn the grammar once and the selection becomes automatic.

The family, decoded

SE style U (SEU) is the flat cable on every meter wall: two insulated hot conductors, wrapped by a bare concentric neutral, strands wound around the insulated pair, all under a sunlight-resistant jacket. Three conductors total. The concentric strands are gathered and twisted into a single neutral at each termination.

SE style R (SER) is round, with three insulated conductors plus a bare equipment ground: four wires. This is the feeder cable, because downstream of the service disconnect the neutral and the equipment ground must be separate conductors, a rule inherited from the grounding and bonding subject.

USE is underground service-entrance cable: moisture-rated for direct burial, and commonly dual-rated USE-2/RHW-2. What USE lacks is a flame-rated jacket, and that lack writes its main rule: USE stays outside and underground. It may not run through the interior of a building.

Inside a building, SE cable used for interior feeders and branch circuits follows cable-method rules similar to NM, including, in the pattern most codes now use, the 60 °C ampacity limit for smaller SE cable installed in thermal insulation, with 75 °C available otherwise. Your code’s exact conditions govern; the instinct to carry is that SE indoors is treated like a cable, not like conductors in conduit.

Where each one goes

• Service riser from weatherhead to meter to service disconnect, run on the building exterior: SEU, its bare concentric serving as the grounded service conductor, which the service bonding rules permit on the line side.
• Panel to subpanel, panel to range or dryer, any feeder past the main disconnect: SER, four wires, neutral insulated and ground separate.
• Buried lateral from a pole or pedestal: USE, emerging from the trench and stopping where the building interior begins.

Worked example

A house gets a 200 A service upgrade plus a 100 A subpanel in an attached garage:

1. Weatherhead down to the meter can: SEU, jacket sunlight-resistant, concentric strands twisted and landed on the neutral lugs. Line side of the main, so the bare neutral doubling as the grounded conductor is permitted.
2. Meter to the service disconnect: still line side, still SEU.
3. Service disconnect to the garage subpanel: this is now a feeder. SER, four conductors. The insulated neutral lands on an isolated neutral bar; the bare ground lands on the grounded bar; the bonding stays separated exactly as the grounding subject taught.
4. If the subpanel had been in a detached shop fed by trench: USE in the trench, transitioning at the building line, because USE cannot enter the interior.

SEU in section: two insulated hots, and the neutral is the bare concentric wrap gathered at each end, a line-side-only trick

Where it bites

• USE through the wall. Pulling the buried cable on into the basement to the panel is the classic violation: no flame rating, no interior use. Transition to an interior-rated method at the building line.
• SEU as a feeder. Three-wire SEU to a subpanel forces neutral and ground together downstream of the service disconnect, recreating the parallel-path problem from the grounding subject. Feeders get SER’s four wires. Older installs grandfathered under three-wire rules are exactly that: older.
• Forgetting the concentric is the neutral. Every strand gets gathered and terminated. Stray strands left against the can are stray neutral paths.
• Ampacity by assumption. SE indoors does not automatically get the 75 °C column; insulation contact and cable size change the answer, and the code’s conditions decide. Look it up per installation.
• Sunlight resistance is a listing, not a color. The riser jacket must be marked sunlight-resistant; gray does not certify anything.