How to Install a 100 Amp Breaker Box | Permits & Wiring

Installing a 100-amp breaker box is a licensed electrical project that starts with a permit and ends with an inspection.

One wrong connection at 120/240 volts can energize a metal enclosure or start a fire, so the order of work matters more than the tools. A 100-amp breaker box install begins with the permit office, then moves through panel selection, feeder sizing, mounting, wiring, and bonding—in that order. This guide walks through each stage, what to buy, and the mistakes that fail inspections.

Choose The Right 100-Amp Load Center

The right 100-amp load center for a home is a UL-listed main-breaker panel with enough spaces for the branch circuits it will feed. A main-breaker panel has the primary disconnect built in, which makes it the standard choice for a service entrance. A main-lug panel has no main breaker and is meant for subpanels or setups where an upstream disconnect already exists.

Eaton’s Type BR line is a common example for US residential systems. The BRP10B100 is a 100-amp, 120/240 V AC, single-phase main-breaker load center with 10 spaces and 20 poles, an aluminum bus, a NEMA 1 indoor rating, and a 10 kAIC interrupting rating. It accepts #6–1/0 AWG copper or aluminum conductors, which covers the feeder sizes used for 100-amp services.

If you are at the buying stage, our tested picks for the best 100 amp breaker box narrow the field by configuration and value.

Match The Feed And The Breakers

The feeder wires and the branch breakers must match both the panel rating and the panel brand family. A 100-amp feeder usually means 2 AWG copper or 1/0 AWG aluminum for the hot and neutral conductors, with a properly sized ground wire, but local code and conduit type can change that sizing.

Breakers are not interchangeable between brands. Eaton Type BR breakers belong in Eaton BR panels; Square D breakers belong in Square D panels. Mixing families is one of the fastest ways to fail inspection or create a loose connection that heats up over time.

Eaton’s own Type BR loadcenter catalog also sets a specific limit for 100-amp and 125-amp loadcenters: the sum of handle ratings connected to any single stab is limited to 150 amps maximum. Overloading a stab by stacking large breakers next to each other is a real, spec-level constraint that many DIY installs miss. The same catalog notes that some models are convertible between a 100-amp main breaker and a 125-amp main lug, so read the label on the exact panel you buy rather than assuming.

The Installation Sequence, In The Order That Passes Inspection

A code-compliant 100-amp panel install follows a fixed sequence: pull the permit, kill the power, mount the enclosure, land the feeder, install branch breakers, bond the grounds correctly, then call for inspection. Skipping or reordering any of these steps is where work gets rejected.

Mount the enclosure first, level and secure, with the main breaker at a proper working height. Land the feeder into the main lugs, torque the terminals to the panel’s label specs, and route the branch circuits so the panel interior stays neat enough for the inspector to trace every conductor.

Bonding depends on panel type. In a main service panel, the neutral is bonded to the ground bar and the enclosure. In a subpanel, the neutral must be isolated and the grounds separated. Getting this backwards is a classic failed inspection and a shock hazard.

Eaton’s Type BR loadcenter catalog documents the ratings, application limits, and family compatibility that apply to these panels. Installations must also follow the US National Electrical Code and local permit rules, which the catalog does not replace.

Before you close the panel, do these three final checks: every breaker is the correct Type BR family, no stab is loaded past the 150-amp handle-sum limit, and the neutral and ground bars are bonded or isolated exactly as the panel type requires. When those three things are right, the panel is ready for the inspector’s sign-off.

FAQs

Do I need a permit to install a 100-amp breaker box?

Yes, in virtually every US jurisdiction. A 100-amp service panel is a substantial change to the electrical system, and local building departments require a permit plus an inspection before the work is considered legal. Unpermitted panel work can create insurance problems when you sell the house, so the permit is not optional paperwork.

What is the difference between a main-breaker and a main-lug panel?

A main-breaker panel contains the main disconnect inside the enclosure, so it can serve as the service entrance where power first enters the house. A main-lug panel has no main breaker and is used downstream as a subpanel, or where a separate upstream disconnect already exists. Choosing the wrong type for your setup fails inspection.

Can I use any breaker brand in a 100-amp panel?

No. Breakers must come from the same manufacturer family as the panel. Eaton Type BR breakers are designed for Type BR loadcenters, and breakers from other brands are not listed for that panel. Installing a mismatched breaker voids the panel’s listing and can create a loose, overheating connection.