How to Choose the Right Circuit Breaker

Ordering the wrong circuit breaker means downtime and return shipping. These are the six specifications that determine whether a breaker is right for your application — match them all and you'll get the correct part every time.

1. Breaker type

Molded-case circuit breakers (MCCBs) cover the vast majority of commercial and industrial branch and feeder applications. Insulated-case (ICCBs) and low-voltage power breakers handle higher currents and offer more advanced trip settings. Miniature breakers (like Square D QO/QOB) serve load centers and panelboards. Identify the family first — it narrows everything else.

2. Frame size

The frame designates the physical breaker family and its maximum amperage — for example Square D's FA, KA, LA, MA and NA frames. Replacement breakers must match the frame that fits your panel or switchgear. When matching an existing unit, the frame is usually the first few letters of the catalog number.

3. Amperage (trip rating)

The ampere rating is the continuous current the breaker will carry before tripping. It must match the circuit it protects — sized to the conductor and load per the NEC. Common ratings run from 15 A up to 2,000+ A depending on frame.

4. Voltage rating

Confirm the breaker's voltage rating meets or exceeds your system voltage — 240 V, 480 V, or 600 V AC are typical. Using a breaker rated below system voltage is unsafe; using one rated higher is generally fine.

5. Number of poles

1-pole for single-phase 120 V branch circuits, 2-pole for 240 V, and 3-pole for three-phase systems. The pole count must match your circuit configuration.

6. Interrupting rating (AIC)

The interrupting rating (kAIC) is the maximum fault current the breaker can safely clear. It must equal or exceed the available fault current at its point of installation. This is a safety-critical spec — never downgrade it when substituting a breaker.

The fastest path: match the catalog number

If you're replacing an existing breaker, the catalog/part number on the nameplate encodes most of these specs. Match it exactly when you can. If it's discontinued, note the six specs above and we'll help you find an equivalent.

Browse circuit breakers by brand, frame and amperage, or contact us with your part number and we'll source it.