Electrical Service Entrance Components Explained
A service entrance is everything between the utility's point of delivery and a building's main disconnect, and NEC Article 230 defines exactly where that boundary sits and what each component along the way is responsible for. Understanding this chain matters for more than terminology: it determines who owns and maintains each piece, where permits and inspections apply, and how a service upgrade actually works when a building needs more capacity. Every service entrance eventually terminates in a main disconnect and a panel protected by correctly sized circuit breakers. This guide walks through each component from the utility connection to the main panel, in order.
Where the Service Entrance Begins and Ends
The service entrance starts at the service point, the location where the utility's wiring connects to the customer's wiring, and ends at the line terminals of the service disconnecting means. Everything downstream of that disconnect is a feeder or branch circuit, governed by different NEC articles; everything at or upstream of it, up to the point of utility attachment, is the service entrance itself, governed by Article 230. This boundary also marks a shift in ownership and responsibility: the utility typically owns and maintains the conductors and equipment up to the point of attachment, while the property owner and their electrical contractor are responsible for everything from that point through the main disconnect.
Service Entrance Components in Order
|
Component |
What It Does |
|---|---|
|
Service drop or lateral |
The utility-owned conductors delivering power to the property; overhead (drop) or underground (lateral) |
|
Weatherhead (service head) |
A curved, raintight fitting at the top of the service mast preventing water from entering the conduit where overhead conductors connect |
|
Service mast |
The rigid conduit riser providing structural support and the required clearance height for overhead conductors |
|
Meter socket (meter base) |
Houses the utility's kilowatt-hour meter; the demarcation point between utility and customer equipment |
|
Service entrance conductors |
Run from the meter socket to the main disconnect, sized per NEC Table 310.12 for the service ampacity |
|
Main disconnect |
A single means to disconnect all ungrounded conductors from the building at once, required to be readily accessible |
|
Grounding electrode system |
Connects the service to the earth via a ground rod, water pipe, concrete-encased electrode, or similar recognized electrode |
Overhead Service Drop vs. Underground Service Lateral
An overhead service drop runs from a utility pole to the building's weatherhead, typically using triplex or quadruplex cable, insulated phase conductors twisted around a bare neutral that also serves as the messenger wire supporting the whole assembly's weight. An underground service lateral runs in conduit or as direct-buried cable from a pad-mounted transformer or junction vault to the meter base, using conductors rated for direct earth contact where not run in conduit. Underground service avoids the weatherhead and overhead clearance requirements entirely but requires excavation and, in many areas, coordination with the utility on conduit routing and depth before the trench is closed.
The Weatherhead and Service Mast
NEC 230.54 requires a raintight service head at the point where service conductors enter the raceway from outside, positioned above the point of attachment except where impracticable, in which case it can sit up to 24 inches below. The service mast has to be strong enough to support the weight and wind load of the overhead conductors it carries, and clearance heights are strictly enforced: NEC 230.24 generally requires at least 10 feet above grade for areas like driveways, rising to 12 feet or more over areas subject to vehicle traffic, with local utility tariffs sometimes specifying even greater heights. Drip loops, a deliberate sag formed in each conductor before it reaches the weatherhead, direct water away from the conduit and provide strain relief.
The Meter Socket
The meter socket houses the utility's kilowatt-hour meter and is the specific point most utilities treat as the metering demarcation for billing purposes. The enclosure itself is typically customer-furnished but must be a model the utility approves, and the utility retains exclusive rights to break the meter seal; tampering with it is both a safety issue and, in most jurisdictions, a legal one. On most residential dials, values are read left to right, though each successive dial rotates in the opposite direction from its neighbor, a detail that matters for manually reading an older analog meter correctly.
Service Entrance Conductors
These conductors run from the meter socket to the main disconnect and are sized according to NEC Table 310.12 based on the service's rated ampacity; a typical 200-amp residential service commonly uses 2/0 AWG aluminum or 4/0 AWG copper conductors, though exact sizing depends on the specific conductor type, insulation, and any adjustment factors that apply. These conductors can run as individual conductors in conduit or as a pre-assembled service entrance cable, and the correct type depends on whether the installation is exposed, run through conduit, or direct-buried.
The Main Disconnect
NEC 230.70 requires the service disconnecting means to be located at a readily accessible point, either outside the building or as close as practical to the point where conductors enter it, and it must be capable of disconnecting all ungrounded service conductors simultaneously with one action. Depending on the design, this can be a single large breaker, a fused switch, or in some designs a set of up to six disconnects operated together. In many installations, the main disconnect and the main distribution panel are the same enclosure; in others, particularly where the panel is located well inside the building, a separate externally operated (EXO) disconnect switch sits between the meter and the interior panel.
The Grounding Electrode System
Every service requires a connection to a grounding electrode, most commonly a driven ground rod, but also potentially a metal underground water pipe, a concrete-encased electrode, or the metal frame of the building, per NEC 250.50. Where more than one qualifying electrode is present, all of them must be bonded together to form a single grounding electrode system rather than being treated as independent, isolated grounds. This system stabilizes system voltage relative to earth and works alongside, not instead of, the equipment grounding conductors that run through the building's branch circuit wiring.
Service Upgrades: Why They Touch the Whole Chain
Increasing a service's rated capacity, from 100 amps to 200 amps, for example, isn't a matter of just swapping the panel; it typically requires replacing components from the weatherhead through the main disconnect, since the service drop or lateral, the meter socket, and the service entrance conductors all have to be rated for the new higher ampacity as well. This is why a service upgrade is treated as a full-scope project requiring a permit, utility coordination for the meter set, and final inspection before the utility will reconnect service. Enclosures exposed to weather, including any NEMA-rated enclosure added as part of the upgrade, need a rating appropriate to the installation's actual outdoor exposure.
The Bottom Line
A service entrance is the complete chain from the utility's point of delivery to a building's main disconnect: the service drop or lateral, the weatherhead and mast for overhead service, the meter socket where the utility measures consumption, the service entrance conductors, the main disconnect, and the grounding electrode system tying it all to earth. The utility generally owns and maintains everything up to the point of attachment, while the property owner is responsible for the meter socket through the main disconnect. Because a service upgrade touches nearly every component in that chain rather than just the panel, it's treated, correctly, as a significant project requiring a permit, utility coordination, and inspection rather than a simple parts swap.