When wiring a modern residential service, the meter base and disconnect wiring diagram dictates how utility power transitions into your home's branch circuits. For a standard 200-amp, 240-volt split-phase service, power enters the line-side lugs, passes through the meter socket jaws, feeds the main disconnect breaker, and terminates at the load-side bus bars. The neutral-to-ground bond occurs exclusively at this main disconnect point. Below is the exact terminal map, a node-by-node trace, and the decision framework to select and verify your specific hardware.
The Direct Answer: Standard 200A Meter-Disconnect Terminal Map
The physical layout of a 200A meter-main combo (such as a Milbank U4198-XL or Siemens W0408MB1200CT) follows a strict top-down or side-to-side flow. This spec-sheet-table maps the exact terminals you will encounter on the physical device. Assumption: This table assumes 75°C rated terminations and 2/0 AWG Copper or 4/0 AWG Aluminum conductors, which are the standard minimums for a 200A residential service per NEC Table 310.16.
| Terminal / Lug Name | Physical Location | Wire Color / Type | Function & Torque Spec |
|---|---|---|---|
| L1 Line Lug (Phase A) | Top Left (Line Side) | Black (THHN/XHHW) | Utility 120V Phase A input. Torque: ~250 in-lbs (verify label). |
| L2 Line Lug (Phase B) | Top Right (Line Side) | Red (THHN/XHHW) | Utility 120V Phase B input. Torque: ~250 in-lbs. |
| Neutral Line Lug | Top Center (Line Side) | White / Gray | Utility grounded conductor input. Torque: ~250 in-lbs. |
| Meter Jaws (1, 2, 3, 4) | Center Socket Area | Internal Bus Stabs | Jaws 1 & 3 receive line power; 2 & 4 feed the main breaker. |
| Main Breaker Lugs | Directly below Meter Socket | N/A (Internal) | Receives metered power from jaws 2 & 4. |
| Load Bus Bars (L1/L2) | Bottom Section (Load Side) | Branch Circuit Wires | Distributes 240V/120V to branch breakers. |
| Neutral/Ground Bus Bar | Side or Bottom (Load Side) | White, Bare, Green | Branch neutrals and equipment grounds. Contains the main bonding jumper. |
Node-by-Node Trace: Utility Drop to Load Bus
To read a meter base and disconnect wiring diagram correctly, you must trace the path from the source (utility transformer) to the load (branch circuits). Here is the exact sequence, including what the standard schematic symbols represent in this drawing.
1. Utility Source to Line-Side Lugs
The utility drop (overhead) or lateral (underground) feeds three conductors into the top of the enclosure. In schematics, this is represented by three parallel lines entering a rectangular box. Polarity is critical here: Phase A (L1) and Phase B (L2) must land on their respective isolated line lugs. The grounded neutral lands on the isolated neutral lug. At this node, the neutral is not bonded to the metal enclosure.
2. Line Lugs to Meter Jaws
Internal bus bars route L1 and L2 from the line lugs to Meter Jaws 1 and 3. The neutral routes to Jaw 5 (or a continuous neutral strap, depending on the socket design). On a wiring diagram, the meter socket is depicted as a circle with internal horizontal stabs. The utility installs the watt-hour meter here, which bridges Jaws 1-to-2 and 3-to-4 via its internal current coils.
3. Meter Jaws to Main Disconnect
Power exits the meter socket via Jaws 2 and 4, traveling down heavy internal bus stabs to the line-side lugs of the 200A main breaker. The schematic symbol for the main disconnect is a square with a diagonal line or a switch symbol indicating the manual toggle. This breaker provides the single-point disconnect required by NEC 230.70.
4. Main Disconnect to Load Bus and Ground Path
When the main breaker is ON, power flows to the load-side plug-on or bolt-on bus bars. Here, the ground path is established. On the diagram, you will see a zig-zag line or a solid line connecting the neutral bus to a triangle pointing down (the earth ground symbol). This represents the Main Bonding Jumper (MBJ) or green bonding screw. This is the exact physical point where the grounded neutral conductor is bonded to the equipment grounding system and the metal enclosure. Downstream of this point, neutral and ground must remain strictly separated.
Field Verification: Testing Your Connections with a Multimeter
Never assume a diagram matches physical reality. After the utility energizes the line side, but before closing the main disconnect, you must verify the wiring. Safety Warning: The line-side lugs remain live even when the main breaker is OFF. Wear Category 2 arc-flash PPE and use a CAT III/IV rated multimeter.
- Verify Line-Side Voltage (Polarity Check): With the main breaker OFF, place probes on the L1 and L2 line lugs. You must read between 235V and 245V. Next, measure L1 to Neutral and L2 to Neutral. Both must read between 117V and 125V. If L1-to-Neutral reads 240V and L2-to-Neutral reads 0V, your utility neutral is floating or miswired—do not proceed.
- Verify Load-Side Voltage: Turn the main breaker ON. Measure the load-side bus bars (L1 to L2, L1 to Neutral, L2 to Neutral). The readings should match the line-side readings within 1-2 volts. A drop greater than 3V across the main breaker under no-load indicates a defective breaker or loose internal stab connection.
- Verify Ground Bond Continuity (De-energized Test): This must be done before utility energization. Set your meter to the lowest Ohms setting. Place one probe on the neutral bus bar and the other on the equipment ground bus bar (or the bare metal enclosure). You must read less than 0.5 ohms. This confirms the main bonding jumper is installed and making solid contact. If you read OL (open loop), the bond is missing, and a ground fault will not trip the breaker.
Decision Tree: Choosing Your Meter-Disconnect Configuration
Selecting the right meter-main combo depends on your future power plans. Use this decision-tree-table to terminate on a concrete hardware pick.
| If Your Scenario Is... | Then Choose This Configuration | Concrete Part Number Pick |
|---|---|---|
| Standard new construction, no solar or battery backup planned, simple utility net-metering not required. | Standard 200A Ringless Meter-Main with 4 branch spaces for exterior receptacles. | Milbank U4198-XL-8MG (Approx. $380-$450) |
| Planning to install rooftop solar within 2 years, requiring a dedicated solar backfeed breaker and utility-visible disconnect. | Solar-Ready Meter-Main with a separate, isolated solar bus or dedicated high-amp breaker spaces at the bottom. | Siemens MC2442MB1200SOLAR (Approx. $650-$750) |
| Installing a whole-home battery backup system (e.g., Tesla Powerwall, Enphase IQ) requiring automatic transfer. | Smart Meter-Main with integrated automatic transfer switch (ATS) and backup load center. | Generac PWRcell G04100A or Eaton BI-PLEX (Approx. $1,800-$2,500) |
The Default Recommendation: If you are pulling a permit today for a standard home and want maximum flexibility without paying the premium for an integrated ATS, buy the Siemens MC2442MB1200SOLAR. The extra $200 over a standard Milbank unit provides a factory-installed solar-ready bus, saving you from having to rip out the meter base when you eventually add PV panels, and it easily handles standard branch circuits in the meantime.
Critical Safety and NEC 2026 Grounding Rules
When executing this wiring diagram, adherence to the National Electrical Code (NEC) is non-negotiable for fire and shock prevention. According to NFPA 70 (NEC) Article 250.24, the grounding electrode conductor (GEC) must connect to the grounded service conductor (neutral) at the service disconnecting means.
In a meter-base and disconnect combo, this means your #4 AWG bare copper GEC running to the ground rods or ufer ground must land on the same neutral/ground bus bar that contains the main bonding jumper. Do not route the GEC to a separate ground bar that is isolated from the neutral. Furthermore, NEC 408.40 dictates that the equipment grounding bar must be securely bonded to the metal enclosure. If your specific panel model ships with an isolated ground bar for subpanel use, you must install the included green bonding screw or strap to tie it to the neutral bus for this specific main-disconnect application.
For deeper code analysis on service grounding and bonding jumper sizing, Mike Holt's NEC resources provide excellent visual breakdowns of Article 250. Always verify your final lug torque with a calibrated inch-pound torque screwdriver; loose neutral connections on the line side are the leading cause of residential service fires due to neutral shift and overvoltage on 120V branch circuits.
