Service Entrance

Part of Power Transmission

The connection point between community distribution lines and individual building wiring.

Why This Matters

The service entrance is the transition point between the community power distribution system and a building’s internal electrical system. It is where the line connection is made, where main overcurrent protection is installed, where metering occurs, where grounding is established, and where the building owner’s responsibility begins and the community grid’s responsibility ends.

A properly designed service entrance protects the building, the grid, and the people inside. It provides a clear demarcation between systems maintained by different people, enables safe maintenance through the main disconnect, and ensures any fault inside the building causes only that building’s protection to operate without affecting the rest of the grid.

A poorly designed service entrance creates multiple hazards: water enters the building through unsealed wire penetrations; inadequate overcurrent protection allows building fires from overloaded wiring; missing main disconnect makes emergency de-energization impossible; improper grounding creates shock hazards from touched metal surfaces. Every building connected to a community grid deserves a complete, well-installed service entrance.

Service Entrance Components

Service Drop

The overhead or underground cable from the distribution line to the building.

Overhead service drop: Three or four conductors running from the last pole (or transformer) to the building. In single-phase split systems: two hot conductors and one neutral. In three-phase systems: three hots and one neutral.

Service drop wire is typically larger gauge than indoor wiring because it is exposed to weather and temperature extremes without conduit protection. Minimum outdoor service drop wire:

• Under 100A service: 2 AWG aluminum or 4 AWG copper
• 100–200A service: 2/0 (double-ought) aluminum or 1/0 copper

Service drop clearances:

• At the building: 3m above any accessible roof or surface
• Over a pedestrian path: 5m minimum
• Over a vehicle road: 6m minimum
• Point of attachment to building: minimum 3m above grade, or above any window the wire passes near

Underground service entrance: Cable runs underground from the pole or transformer to the building. Uses direct-burial-rated cable (type USE or equivalent) or conduit with standard wire.

Advantages: no overhead clearance concerns, protected from wind and ice, not visible. Disadvantages: requires trenching, vulnerable to digging damage, cannot visually inspect for damage.

Underground installation depth: Minimum 60cm under pedestrian areas; 90cm under vehicle paths. Mark the cable route with permanent markers visible at grade level. Document the exact route before burying.

Weather Head (Service Head)

The point where the overhead service drop enters the building must be weatherproofed. A weather head (service head) is a curved metal conduit fitting that points the conduit end downward and outward, so rain cannot enter the conduit and run down into the building.

Construction:

1. A length of conduit passes through the building wall at a slight upward angle
2. A curved head fitting at the exterior end points the opening toward the ground
3. The service drop conductors enter through the bottom of the weather head, making a “drip loop” (the conductor dips below the weather head before entering, so water runs down to the drip loop and falls off rather than running into the conduit)
4. Sealant around the conduit at the wall penetration prevents water infiltration

The drip loop is essential. Without it, water running down the conductor during rain enters the conduit and finds its way inside the building wall.

Main Disconnect

The main disconnect must be able to de-energize the entire building from a single operation. Requirements:

• Accessible from outside: Emergency responders must be able to cut power without entering the building. Place the disconnect at the exterior service entrance, not inside the building.
• Labeled: Permanent marking showing this is the main disconnect
• Single operation: One switch or breaker that interrupts all ungrounded conductors simultaneously
• Appropriate rating: Rated for the maximum current the service can deliver

For a single-phase service, a two-pole breaker interrupts both hot conductors simultaneously. For three-phase, a three-pole breaker interrupts all three hots.

Lockout capability: The main disconnect should have a locking provision — a padlock hasp that prevents anyone from re-energizing the building while maintenance is in progress. This is the foundation of lockout/tagout procedure for electrical safety.

Meter Socket

Where usage is tracked, the meter socket provides the connection point for the energy meter. The standard socket consists of terminal jaws that grip the blade-type meter contacts. The meter plugs into the socket; all current flows through the meter for measurement.

Meter position in the circuit: The meter must measure all energy entering the building. Install between the service drop and the main disconnect — if it is installed downstream of the disconnect, de-energizing for maintenance also kills the meter (harmless) but also creates a section of live wiring between the service drop and the meter (potentially dangerous if someone assumes the whole service entrance is de-energized).

Building your own meter socket: Commercial meter sockets are standardized. If unavailable, a simpler metering point using a shunt resistor and voltmeter (see Metering) gives adequate consumption data for a community allocation system.

Service Entrance Panel

Inside the building, the service entrance panel (main panel, load center) distributes power to individual branch circuits. Components:

Main lugs or main breaker:

• If main disconnect is at the exterior service entrance, the panel inside can have main lugs (wire terminals) rather than a main breaker — the building is de-energized externally
• If the exterior disconnect is minimal (weather head with fuse only, no switch), install a main breaker inside as an additional disconnect

Bus bars:

• Hot bus bars (one per phase): The source terminals for all branch circuit breakers. These are live whenever the main is closed.
• Neutral bus bar: All neutral wires from branch circuits terminate here. In the main service panel, the neutral bus is bonded to the ground bus and to the system ground (ground rod connection).
• Ground bus bar: All equipment ground wires terminate here. In a sub-panel (a second panel fed from the main), the ground and neutral buses must be separate and not bonded to each other.

Branch circuit breakers: Individual breakers or fuses for each circuit in the building. Each must be rated for its circuit’s wire gauge.

Grounding at the Service Entrance

The service entrance is where system grounding is established. Three grounding connections are made here:

1. Neutral-to-ground bond: The neutral bus bar and ground bus bar are connected by a bond wire inside the main panel. This occurs only at the main panel, never at sub-panels or at the generator end of a separately-derived system.

2. Ground rod connection: A heavy wire (minimum 4 AWG copper or 2 AWG aluminum) runs from the ground bus bar to one or more ground rods driven at least 2m into the earth near the building. If the first ground rod shows resistance over 25 ohms (test with a ground resistance meter), drive a second rod at least 2m away and connect both to the ground bus.

3. Equipment ground: All metallic conduit, equipment enclosures, outlet boxes, and appliance frames connect to the ground bus through the green/bare ground wire of each branch circuit. If any fault occurs (live conductor contacts a metal enclosure), current flows to ground through this intentional low-resistance path, immediately tripping the circuit’s overcurrent protection.

Water pipe bonding: If the building has a metallic water pipe system, bond the pipes to the ground bus at the service entrance using a clamp connector and heavy wire. Water pipe systems may serve as an unintended current path and must be bonded to the electrical ground to prevent shock hazards from ground potential differences.

Inspecting a Salvaged or Existing Service Entrance

Before connecting to an existing building’s service entrance, inspect:

Water intrusion: Corrosion on wires, rust staining, or dampness inside the panel box all indicate water entry. Find and seal the entry point before energizing. Wet electrical connections cause corrosion, increased resistance, and eventual arcing.

Correct wire terminations: Every wire must be terminated in a lug or under a screw — no bare conductors simply twisted around other wires. Check that all screws are tight.

Fuse/breaker condition: Test every breaker. Look for blown fuses, melted or discolored fuse holders, or breakers with tripped positions stuck (will not reset).

Neutral-to-ground bond: Verify that the neutral and ground are bonded at this panel if it is the main panel. Verify they are not bonded if this is a sub-panel.

Wire sizes: Verify that each breaker is no larger than the wire it protects. Look for evidence of “over-fusing” (breaker replaced with higher-rated one without upgrading wire) — the most common cause of electrical fires in improvised or poorly maintained systems.