Service Entrance Symbol
Definition: The Service Entrance symbol represents the utility supply interface point in an electrical wiring diagram — the point at which the electrical utility's conductors enter a building or structure and connect to the customer's main panel, as defined in NFPA 70 (National Electrical Code) Article 230 and identified by IEC 60617 as the origin of installation symbol.
Also known as: service entry, utility connection point, weatherhead, service mast, service drop termination, origin of installation.
What the Service Entrance symbol means
The Service Entrance symbol marks the boundary between the utility company's wiring and the customer's electrical installation. It indicates where the utility meter feeds the main service panel through the service conductors (service drop overhead or service lateral underground). Everything upstream of the service entrance is the utility's responsibility; everything downstream is the customer's installation.
In a residential or commercial wiring diagram, the service entrance symbol is placed at the top of the riser diagram between the utility transformer or overhead lines and the meter base, establishing the supply voltage level, the number of conductors (single-phase 2-wire, single-phase 3-wire, or 3-phase), and the path through which power enters the building.
How to identify the Service Entrance symbol
The service entrance symbol typically appears as a simplified mast or riser graphic: a vertical line (representing the service mast or conduit) with a curved top indicating the weatherhead, terminating at the utility connection point above. Two pins are shown — a Utility pin at the top (incoming from utility) and a Panel pin at the bottom (exiting toward the main panel or meter). In schematic diagrams it may be simplified to a labelled source symbol or utility-feed node.
Function in a circuit
The service entrance is the functional starting point of the customer's electrical system. It establishes the available fault current (ISC) from the utility, the nominal supply voltage and frequency, and the number of phases, all of which determine the specifications of the main disconnect, meter, and panel equipment. The service entrance conductors carry the full building load current and must be sized per NFPA 70 Article 230 and IEC 60364-5-52 for voltage drop and ampacity.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60364-1 (Section 313) defines the 'origin of installation' as the point where the installation receives its supply from the distribution network. IEC 60617 uses a general supply-source symbol at the origin of installation; no dedicated service-entrance glyph is standardised. |
|---|---|
| ANSI/IEEE 315 | NFPA 70 (NEC) Article 230 is the primary North American standard governing service entrances, defining requirements for conductors, clearances, disconnecting means, and metering. ANSI Y32.2 / IEEE 315 does not define a unique service-entrance symbol; wiring diagrams use a source or utility-feed annotation. |
| Key difference | IEC 60364 uses the term 'origin of installation' while NEC Article 230 uses 'service entrance'. Graphically both traditions represent this point as a labelled supply node. The NEC additionally requires a visible and accessible main disconnect within sight of the service entrance or at the service entrance itself. |
Terminals / pins
| Pin | Name |
|---|---|
| utility | Utility |
| panel | Panel |
Typical values
North American residential: 120/240 V single-phase 3-wire (split-phase), 60 Hz. Typical service sizes: 100 A, 150 A, 200 A, 400 A (residential to small commercial). European/IEC: 230/400 V 3-phase 4-wire, 50 Hz. Minimum clearance above grade for overhead service conductors: 3.0 m (10 ft) over walkways, 4.5 m (15 ft) over driveways (NEC 230.24).
Where the Service Entrance symbol is used
- Residential riser diagrams showing the complete electrical supply path from utility pole to main panel
- Commercial load calculations establishing the available fault current and required interrupting rating of main breakers
- Solar PV and energy storage interconnection diagrams showing grid connection point relative to main service entrance
- EV charger installation drawings marking the utility interface and service capacity available for load addition
- Generator standby power systems: the service entrance is the reference point for the automatic transfer switch
- Electrical permit drawings submitted to authorities having jurisdiction (AHJ) — the service entrance location is a required element
Example
In a residential electrical riser diagram, the Service Entrance symbol sits between the utility overhead conductors (Utility pin) and the 200 A main meter base, with the Panel pin feeding the main service panel below. The symbol annotates the service voltage (120/240 V), number of conductors (2 hot + 1 neutral), and the available fault current from the utility (e.g. 10 kA ISC), which governs the AIC rating of the main breaker.
Key facts
- The Service Entrance symbol marks the boundary between utility-owned conductors and customer-owned wiring; everything downstream is governed by NEC Article 230 (USA) or IEC 60364-1 (international).
- NEC Article 230 requires a main disconnect (service disconnect) at or near the point of entry, rated for the full service current (100 A minimum for residential per NEC 230.79).
- The two symbol pins are Utility (incoming from the supply network) and Panel (outgoing to the main service panel or meter base), with the meter socket inserted between them in most installations.
- Available fault current (ISC) at the service entrance determines the minimum interrupting capacity (AIC or KAIC rating) of the main circuit breaker per NEC 110.9 and UL 489.
- Overhead service entrances require a weatherhead (service head) at the top of the service mast to prevent water ingress into the service conduit — this is what the curved top of the symbol represents.
- North American residential service is typically single-phase 3-wire 120/240 V (split-phase); European residential service is single-phase 230 V from a 3-phase 400 V network.
- Solar PV systems with grid-tie inverters must connect downstream of the service entrance meter per NEC 690 and utility interconnection agreements, making the service entrance the reference point for all distributed generation.
Frequently asked questions
What does the service entrance symbol mean in a wiring diagram?
The service entrance symbol marks the point where utility-supplied electricity enters the building. It is the starting point of the customer's electrical installation, showing where overhead or underground service conductors connect to the meter and main panel.
What does the service entrance symbol look like?
The service entrance symbol typically shows a mast or riser line with a curved weatherhead at the top (the Utility pin where overhead conductors connect) and a downward connection (the Panel pin) leading to the meter base and main service panel. In simplified riser diagrams it may appear as a labelled utility-feed arrow or source node.
What standard governs the service entrance in the USA?
NFPA 70, the National Electrical Code (NEC), Article 230 governs service entrances in the United States. It specifies conductor sizing, clearances, weatherhead height, metering, and the required main disconnect at or near the service entrance.
What is the difference between the service entrance and the main panel?
The service entrance is the point at which utility conductors enter the building and connect to the meter; the main panel (main service panel or distribution board) is the first point of over-current protection and distribution inside the building. The service entrance feeds the main panel through the meter base.
What voltages are typical at a residential service entrance?
In North America the standard residential service entrance is 120/240 V single-phase 3-wire (split-phase) at 60 Hz. In Europe and IEC countries it is 230 V single-phase (from a 400 V 3-phase network) at 50 Hz. Commercial services may be 208/120 V or 480/277 V 3-phase.
What is the minimum service entrance size for a residential dwelling?
NEC Section 230.79 sets a minimum of 100 A for a one-family dwelling. In practice 200 A is standard for new residential construction to accommodate modern electrical loads including EV chargers and heat pumps.
Where does solar PV connect relative to the service entrance?
Grid-tied solar PV inverter output must connect downstream of the utility meter at the service entrance, either at the main panel bus or a dedicated breaker, per NEC Article 690. The service entrance establishes the grid connection point and available capacity for back-feed from solar generation.
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