To install a 200-amp main circuit breaker panel, you need a 200A rated load center (such as the Square D HOM200M400C), 2/0 AWG aluminum (or 3/0 AWG copper) service entrance conductors, and a properly sized main bonding jumper. The black and red hot wires land on the main breaker lugs, the white neutral lands on the neutral busbar, and the bare ground lands on the equipment grounding busbar. This guide covers the physical installation, termination, and verification of a 200-amp main service disconnect.

CRITICAL MAINS SAFETY WARNING: Working on a service entrance panel involves lethal utility-side voltage that cannot be shut off by a breaker. Before beginning, the utility company must physically disconnect the meter or drop the overhead service. You must treat all service entrance conductors as energized until the utility confirms disconnection and you verify zero voltage with a tested meter. Always pull local AHJ (Authority Having Jurisdiction) permits before starting; NEC-style guidance provided here does not override your local inspector's requirements. For comprehensive safety protocols, review OSHA Electrical Safety standards.

Critical Safety & Permit Requirements

Upgrading or installing a main service panel is not a standard branch-circuit DIY job. The service entrance conductors feeding this panel are protected only by the utility's transformer fuses, which can deliver thousands of amps of fault current. If you drop a wrench across the line-side lugs while the meter is engaged, the resulting arc flash can be fatal.

Coordinate with your local utility to schedule a meter pull. In most jurisdictions, the utility will require an approved rough-in inspection from your local building department before they reconnect power. Ensure your panel schedule, grounding electrode system (GES), and service mast or conduit meet the latest NFPA 70 (NEC) requirements, specifically Article 230 for services and Article 250 for grounding and bonding.

Tools, Materials, and Panel Specifications

Precision matters when terminating large-gauge conductors. Under-torqued lugs cause high-resistance connections that overheat and fail; over-torqued lugs strip threads or snap the conductor strands. NEC 110.14(D) mandates the use of a calibrated torque tool for any connection where a torque value is specified.

Required Tools

  • Calibrated torque screwdriver (inch-pounds) and torque wrench (foot-pounds) with appropriate hex/Allen bits
  • Klein Tools 11-in-1 multi-bit screwdriver and heavy-duty wire strippers
  • Klein or Greenlee 2-inch conduit knockout punch set
  • Non-contact voltage tester (NCVT) and a CAT III or CAT IV digital multimeter
  • Wire brushing tool and anti-oxidant paste (e.g., Noalox) for aluminum terminations

Materials Specification

  • Panel: Square D Homeline 200-Amp 40-Space Main Breaker Load Center (HOM200M400C)
  • Service Cable: 2/0-2/0-2/0-1/0 AL SER (Service Entrance Rated) cable
  • Grounding Electrode Conductor (GEC): #4 AWG bare copper (for connection to ground rods)

Termination & Torque Specification Matrix

The following table dictates the exact landing points and torque values for a standard 200A residential service using aluminum SER cable. Always verify against the manufacturer's label inside the panel door, as values can vary slightly by brand.

Conductor Function Wire Color Gauge (AL / Cu) Termination Point Target Torque
Line 1 (Hot) Black 2/0 AL / 3/0 Cu Main Breaker Lug 1 250 in-lbs
Line 2 (Hot) Red 2/0 AL / 3/0 Cu Main Breaker Lug 2 250 in-lbs
Neutral (Grounded) White 1/0 AL / 2/0 Cu Neutral Busbar 180 in-lbs
Equipment Ground Bare 1/0 AL / #4 Cu Ground Busbar / Lug 140 in-lbs

Step-by-Step Installation and Wire Terminations

With the utility meter pulled and power verified dead, proceed with the physical installation and termination of the service entrance conductors.

  1. Mount the Enclosure and Prep Knockouts: Secure the panel enclosure to the wall studs using appropriate lag screws, ensuring it is perfectly level. Use your knockout punch to open the 2-inch top hub or bottom knockout for the SER cable entry. Install a 2-inch conduit hub or cable clamp to protect the cable jacket from sharp metal edges.
  2. Route and Strip the SER Cable: Feed the 2/0-2/0-2/0-1/0 AL SER cable into the panel. Leave at least 6 to 8 feet of slack inside the enclosure to allow for clean, sweeping bends to the termination points. Strip back the outer gray jacket carefully without nicking the inner conductor insulation. Strip exactly 3/4 inch of insulation from the black, red, and white conductors using a heavy-duty wire stripper.
  3. Terminate the Bare Ground Conductor: Take the bare equipment grounding conductor from the SER cable. Route it directly to the dedicated equipment grounding busbar or the main ground lug at the bottom of the panel. Insert the bare wire fully into the lug hole so no strands are splayed outside. Tighten the set screw with your torque screwdriver to 140 in-lbs. Next, connect your #4 AWG bare copper Grounding Electrode Conductor (GEC) to this same ground busbar and route it outside to your two 8-foot ground rods.
  4. Terminate the White Neutral Conductor: Take the white grounded neutral conductor. Route it to the main neutral busbar (usually located on the left or right side, identifiable by the larger terminal screws and the presence of the main bonding jumper). Brush the aluminum wire with a wire brush, apply a thin coat of Noalox anti-oxidant paste, and insert it into an available lug on the neutral bar. Torque to 180 in-lbs. Critical Note: Because this is the main service disconnect, the neutral bar and ground bar must be bonded together via the factory-installed green main bonding screw or strap. Do not remove this bond.
  5. Terminate the Black and Red Hot Conductors: Take the black Line 1 conductor and route it to the top lug of the 200-amp main breaker. Apply anti-oxidant paste, insert fully, and torque to 250 in-lbs. Repeat this exact process for the red Line 2 conductor on the second main breaker lug. Ensure the cable jacket extends into the panel enclosure but does not crowd the breaker terminals, and that no bare wire is visible outside the breaker lug insulation shield.
  6. Dress the Wires and Install the Dead-Front: Use nylon cable ties to bundle the hots, neutral, and ground neatly along the wire gutters. Ensure no wires cross over the front of the breaker stab contacts. Snap the metal dead-front cover into place and secure it with the provided sheet metal screws. Install the panel cover door.

Verification, Testing, and Common Botches

Before calling the utility to reconnect the meter, perform a final visual and continuity check. Ensure the main breaker is in the OFF position. Verify that all branch circuit neutrals and grounds (if pre-wired) are landed on their respective bars, and that no two wires share a single lug hole unless the lug is explicitly rated and listed for two conductors.

The Verification and Test Sequence

  1. Utility Reconnect: Once the inspector and utility have signed off, the utility technician will reinstall the meter, energizing the line-side lugs of your main breaker.
  2. Initial Voltage Check (Main OFF): With the main breaker still OFF, use your CAT IV multimeter to measure across the line-side lugs (where the utility feeds in). You should read 240V AC (acceptable range: 228V - 252V). Measure from each line-side lug to the neutral bar; you should read 120V AC on both.
  3. Energize Panel: Flip the 200-amp main breaker to the ON position.
  4. Load-Side Verification: Measure across the two busbars (or the load-side lugs of the main breaker). Expected reading: 240V AC. Measure from the Line 1 busbar to the neutral bar: Expected 120V AC. Measure from the Line 2 busbar to the neutral bar: Expected 120V AC.
  5. Ground-to-Neutral Verification: Measure voltage between the neutral busbar and the equipment ground busbar. Expected reading: 0V to 1V AC. Any reading higher than 2V under no-load conditions indicates a faulty utility neutral or a missing main bonding jumper.

Most Common Botch: The Floating (Loose) Service Neutral

The most frequent and destructive mistake made during panel installations is failing to torque the white neutral conductor to the manufacturer's specification, resulting in a loose connection at the neutral busbar.

The Symptom: When a large 120V load (like a space heater, microwave, or hair dryer) turns on, the lights on one leg of the house will dim significantly, while the lights on the other leg will burn blindingly bright. You may hear buzzing from electronics, and sensitive appliances (TVs, computer power supplies) may fail or trip their internal surge protection.

The Physics: A loose service neutral breaks the return path for unbalanced 120V loads. The two 120V legs effectively become a 240V series circuit. The voltage divides inversely proportional to the resistance of the loads on each leg. The leg with the heavier load drops in voltage (e.g., down to 80V), while the leg with the lighter load spikes (e.g., up to 160V+), destroying 120V electronics.

The Fix: De-energize the panel entirely (pull the meter). Inspect the white neutral termination on the busbar. Brush the aluminum wire, apply fresh anti-oxidant paste, reseat it fully in the lug, and torque it exactly to 180 in-lbs using a calibrated tool. Never rely on "hand-tight plus a quarter turn" for service entrance conductors.