When electricians and DIYers search for a utility meter wiring diagram, they are almost always looking for the wiring schematic of the meter socket (also called a meter base), not the sealed glass or plastic meter itself. The utility company (POCO) owns and seals the actual metering device. Your responsibility—and the focus of this guide—is wiring the socket that bridges the utility's service drop to your home's main breaker panel.

For a standard North American residential service, this means a single-phase, 3-wire, 120/240V system. The direct answer for a modern 200A service requires 4/0 AWG aluminum or 2/0 AWG copper conductors, terminated at specific line and load jaws with precise torque values. Below, we break down the physical terminal layout, trace the current path node-by-node, and explain how to verify your work before the POCO sets the meter.

Terminal Mapping & Physical Layout

The most common residential enclosure is the 4-jaw ring-type meter socket (e.g., Milbank M4096 or Siemens W0542). The diagram symbols for the "jaws" represent the spring-loaded contacts that grip the blades of the utility's meter. Getting the Line vs. Load orientation correct is critical: while reversing them won't stop the meter from spinning (it measures series current), it violates NEC code and leaves the socket's load-side bus energized even when the main breaker is off, creating a severe arc-flash hazard during panel work.

NEC 110.14(D) Torque Requirement: Since the 2017 NEC cycle, all terminations must be torqued to the manufacturer's specifications using a calibrated torque tool. Hand-tightening is no longer code-compliant and is a leading cause of thermal failures at the meter socket.
200A 4-Jaw Meter Socket Terminal Specifications (4/0 AWG Aluminum XHHW-2)
Terminal / Jaw Physical Location Function Wire Size Torque Spec
Jaw 1 (Top Left) Upper Left Lug Line A (Phase 1 from POCO) 4/0 AWG Al 250 in-lbs
Jaw 2 (Bottom Left) Lower Left Lug Load A (Phase 1 to Panel) 4/0 AWG Al 250 in-lbs
Jaw 3 (Top Right) Upper Right Lug Line B (Phase 2 from POCO) 4/0 AWG Al 250 in-lbs
Jaw 4 (Bottom Right) Lower Right Lug Load B (Phase 2 to Panel) 4/0 AWG Al 250 in-lbs
Neutral Bus Center / Bottom Horn Neutral Return Path 4/0 AWG Al 250 in-lbs
Ground Lug Enclosure Wall / Bottom GEC to Earth Ground 4 AWG Cu 120 in-lbs

Note: Torque values are typical for Milbank mechanical lugs with 4/0 Al. Always verify against the specific manufacturer's spec sheet inside the enclosure door. Source: Milbank Manufacturing.

Node-by-Node Trace: Source to Load

To understand the diagram, we must trace the current path from the utility transformer to the main breaker, paying strict attention to the grounding path.

1. The Utility Source & Service Drop

Current originates at the pole-mounted or pad-mounted utility transformer. The secondary winding provides a center-tapped 240V supply, yielding three wires: two "hot" legs (Phase A and Phase B, each 120V to neutral, 180 degrees out of phase) and one grounded neutral conductor. These travel via overhead triplex cable or underground URD to your service mast or underground conduit.

2. Weatherhead to Line-Side Jaws

The service entrance conductors pass through the weatherhead and conduit into the top hub of the meter socket.

  • Phase A (Black) terminates at the Top Left Line lug (Jaw 1).
  • Phase B (Red) terminates at the Top Right Line lug (Jaw 3).
These lugs are physically connected to the upper meter jaws. At this point, the circuit is open because the meter is not yet installed.

3. The Meter Bridge & Load-Side Jaws

When the POCO installs the meter, its blades slide into the jaws. The meter's internal current coils complete the series path. Current flows from Jaw 1, through the meter's Phase A coil, and out to Jaw 2 (Bottom Left). Similarly, Phase B flows from Jaw 3, through the meter, to Jaw 4 (Bottom Right). From the Bottom Jaws, the 4/0 AWG load conductors exit through the bottom hub and route directly to the main breaker lugs in your service panel.

4. The Neutral & Grounding Path (Explicit Trace)

The neutral conductor from the POCO lands on the center neutral bus bar in the meter socket. A second 4/0 AWG neutral wire leaves this same bus and runs to the neutral bar in the main panel. Critical Code Caveat: In a standard meter socket, the neutral bus is not bonded to the metal enclosure. The neutral-to-ground bond only occurs at the main service disconnect (the main panel). The Grounding Electrode Conductor (GEC)—typically a bare 4 AWG copper wire—connects to a dedicated ground lug on the meter socket's metal enclosure. This wire runs outside to your grounding electrodes (e.g., two 8-foot copper ground rods or a UFER concrete-encased electrode). This path provides fault clearing and lightning dissipation, but carries zero normal operating current.

Decoding Diagram Symbols & Verification Steps

Electrical blueprints use standardized symbols that can confuse beginners. Here is how to translate the diagram to the physical bench, and how to verify your work using a digital multimeter (DMM) and clamp meter.

What the Symbols Mean

  • The Jaws (Interlocking Crescents): Represent the spring-loaded contacts inside the socket. They are drawn in pairs (Line/Load) to show where the meter blades insert.
  • CT (Current Transformer) Rings: If your diagram shows circles around the hot wires labeled "CT", you are looking at a 400A+ service diagram. Residential 200A services use self-contained meters; commercial services use CTs to step down high current for a low-amp meter.
  • Neutral Bus (Horizontal line with downward ticks): Represents the continuous neutral terminal block. The lack of a diagonal "bonding screw" symbol here confirms it is isolated from the enclosure.
SAFETY WARNING: Never pull a utility meter yourself to verify connections. The line-side jaws remain fully energized at utility fault-current levels (often 20,000+ amps) even when the main breaker is off. Arc flash incidents during unauthorized meter pulling are frequently fatal. Verification of live voltage must be done at the load side (main panel) after the POCO sets the meter and seal. See OSHA Electrical Safety Guidelines for PPE requirements.

How to Verify Connections with a Meter

Once the utility has set the meter, removed the tag, and energized the service, perform these verification steps at the main panel to confirm the meter socket wiring is correct:

  1. Line-to-Line Voltage: Set your DMM to AC Voltage (>300V range). Place probes on the two main breaker line terminals. You should read 240V nominal (acceptable range: 228V - 252V). If you read 0V or 120V, a line jaw is miswired or a POCO fuse is blown.
  2. Line-to-Neutral Voltage: Place one probe on Main Breaker Line A and the other on the Panel Neutral Bar. Read should be 120V nominal. Repeat for Line B. If one reads 120V and the other reads 0V, the neutral connection at the meter socket neutral horn is loose or missing.
  3. Ground-to-Neutral Verification: Measure between the Panel Ground Bar and Neutral Bar. Under zero-load conditions, this should read < 1.0V. If you read significant voltage (e.g., 5V+), you have a loose neutral connection at the meter socket or utility transformer, causing neutral current to seek a path through the ground rod.
  4. Load Balancing (Clamp Meter): With the home under normal load, clamp an AC ammeter around Phase A and Phase B conductors individually. They should be within 10-15% of each other. A massive imbalance indicates a lost neutral or a 240V appliance fault.

Common Wiring Mistakes & Code Caveats

Even experienced tradespeople make errors when rushing a service upgrade. Avoid these common failures:

1. The Meter-Main Bonding Trap

If you are installing a "Meter-Main" combo unit (a meter socket with a 200A breaker built directly below it), the NEC requires the neutral-to-ground bonding jumper to be installed inside this combo unit, and the downstream subpanel must have the bonding screw removed. If you wire a standard meter socket but accidentally install the bonding screw, you create a parallel neutral path on the grounding wire, which can electrocute a plumber working on the home's water pipes.

2. Aluminum Oxide & Anti-Oxidant Paste

Because 4/0 AWG Aluminum XHHW-2 is the standard for 200A services, you must wire-brush the aluminum conductor strands and apply an UL-listed anti-oxidant compound (like Noalox) before inserting it into the mechanical lugs. Aluminum oxidizes rapidly in air, creating a high-resistance layer that generates heat and melts the socket enclosure over time.

3. Ignoring the POCO's Specific Requirements

The National Electrical Code (NEC) governs safety, but the local utility company governs the physical connection. Some POCOs require a specific hub size, a bypass lever for 200A services, or a specific grounding electrode configuration. Always download the local utility's "Service Requirements" (often called the Green Book or Blue Book) before pulling a permit. Your local Authority Having Jurisdiction (AHJ) and the POCO inspector must both approve the socket before the meter is set.