1. Complete Anatomy of a 100-Amp to 200-Amp Service Heavy-Up
Upgrading a home from 100-amp to 200-amp electrical service—known in the trade as a service heavy-up—doubles total available power from 24.0 kW to 48.0 kW at 240 volts. A code-compliant heavy-up is not merely a breaker box swap; it requires replacing every current-carrying component between the utility company's service drop and your dwelling's grounding electrode system so the entire path is rated for 200 amperes continuous duty.
During a standard 1-day heavy-up, the utility company disconnects power at the transformer or weatherhead at 8:00 AM. The licensed electrical crew removes the legacy 100A enclosure and meter base, installs a new 2-inch rigid mast or underground riser, mounts a Class 200 meter-main enclosure with an exterior emergency disconnect, installs a 40-space / 80-circuit interior load center, drives dual 8-foot copper ground rods, and schedules the municipal rough/final inspection for afternoon utility re-energization.
100A Legacy Service vs 200A Heavy-Up Hardware Specification Matrix
| Infrastructure Component | Legacy 100-Amp Service | Modern 200-Amp Heavy-Up | Governing NEC Code Section |
|---|---|---|---|
| Service Entrance Conductors | 4 AWG Copper / 2 AWG Aluminum |
2/0 AWG Copper / 4/0 AWG Aluminum | NEC Table 310.12 |
| Weatherhead Mast Conduit | 1.25" or 1.5" EMT / Thin Conduit |
2.0" to 2.5" Rigid Metal Conduit (RMC) | NEC 230.28 Service Masts |
| Utility Meter Socket | Class 100 (100A Max Jaws) |
Class 200 Lever-Bypass or Ringless Base | Utility Service Handbook |
| Exterior Emergency Disconnect | None (Indoor Main Breaker Only) |
200A Outdoor Meter-Main / Disconnect | NEC 230.85 Mandate |
| Bus Bar & Breaker Spaces | 16 to 20 Spaces (Tandem Crowded) |
40 Spaces / 80 Circuits (Copper Bus) | NEC 408.36 Overcurrent |
| Grounding Electrode Conductor | 6 AWG Copper to Water Pipe Only |
4 AWG Copper + Dual 8-Ft Ground Rods | NEC 250.53 & Table 250.66 |
2. Arc-Fault (AFCI) and Surge Protection (SPD) Requirements on Panel Swaps
Under the 2020, 2023, and 2026 editions of the National Electrical Code (NEC 230.67), every residential service panel replacement must include a Type 1 or Type 2 Surge Protective Device (SPD) installed either integrally inside the service equipment or immediately adjacent to it. This protects sensitive inverter appliances, EV chargers, and HVAC control boards from utility grid switching surges.
3. Utility Coordination & Same-Day Reconnect Timeline
Because a 100A-to-200A heavy-up requires pulling the utility meter, homeowners cannot legally perform this work without utility work-order authorization and municipal electrical inspection release. Our estimator desk coordinates directly with local master electricians who hold same-day disconnect/reconnect authority with major regional utilities.
Technical Questions & Code Clarifications
How long is household power shut off during a 100A to 200A panel upgrade?
A standard residential 200-amp heavy-up requires 5 to 8 hours of utility power disconnection. Power is typically disconnected between 8:00 AM and 9:00 AM and restored between 2:30 PM and 4:30 PM the same afternoon once the municipal inspector clears the installation.
Do I have to upgrade all my home wiring when upgrading to a 200-amp panel?
No. Existing 15-amp and 20-amp branch circuit wiring inside your walls remains intact and is landed onto new breakers in the 200-amp panel, provided the existing cables are in safe condition.
