The Q2M2200MT 200 Amp Circuit Breaker: What It Is, Where You’ll Find It, and Why It’s Still in Service

In the late 1960s, Square D introduced a 200A frame main breaker for some of its residential panels. The frame style was known as the Q2 Series, and while the molded-case body was consistent, the frame was offered with four different hookup configurations, depending on the panel design.

The Q2MT is one of those breakers. Its 200 amp model was the Q2M2200MT (originally listed in the catalog as Q2M-2200MT). It predates modern electronic trip units and was commonly used as a main breaker in residential and small commercial service equipment, long before “smart” panels existed.

This article covers what it is, how it works, where it’s typically found, and why people are still looking for them today.

What Is the Q2M2200MT?

The Q2M2200MT is a 200 amp, 10k AIC rated @ 240 V.AC, thermal-magnetic molded case circuit breaker (MCCB) from the Q2 series. It has lug terminals on the Line (“ON”) side, and the Load (“OFF”) side uses ¼-20 threaded studs that connect directly to the load center's branch bus.

Like its branch breaker counterpart, the QO circuit breaker, it originally featured a VISI-TRIP® indicator that displayed red when the breaker tripped.

It also used heavy-duty copper legs and generous contact surfaces, designed to handle residential service loads reliably over long service lives.

How the Q2M2200MT Works

Like many breakers, the Q2M2200MT uses thermal-magnetic protection, which remains one of the most reliable protection methods ever deployed.

Thermal Protection (Overload)

• Uses a bimetallic element

• Responds to sustained overcurrent

• Trips when heat buildup exceeds safe limits

• Protects conductors and equipment from long-term overloads

Magnetic Protection (Short Circuit)

• Uses electromagnetic force generated by fault current in the conductor path

• Responds instantly to high fault current

• Trips in milliseconds during short circuits

No software.
No sensors.
No calibration menus.

Just physics doing its job.

Where You’ll Typically Find Q2M2200MT Breakers

Despite what marketing copy often implies, these breakers weren’t designed for exotic infrastructure. You’ll most often find them in:

• Older residential service equipment

• Small commercial buildings

• Light industrial facilities

• Agricultural installations

• Retrofit panels where original equipment was retained

In many cases, the panel itself is still listed and serviceable — but the breaker is no longer manufactured.

Why the Q2M2200MT Is Still Relevant

The reason people still search for this breaker has nothing to do with nostalgia.

It’s about compatibility.

When a Q2M2200MT fails, the options are usually:

• Replace the breaker with a direct replacement

• Replace the entire panel or service equipment

For many buildings, replacing the whole service:

• Triggers code upgrades

• Requires permits and inspections

• Increases cost dramatically

• Extends downtime

That’s why drop-in replacements matter.

Common Failure Points (What Actually Goes Wrong)

These breakers earned their reputation for longevity, but decades of service eventually show.

1. Thermal Element Fatigue

• Breaker trips below rated load

• Caused by years of heat cycling

• Common in panels that ran near capacity

2. Contact Wear

• Pitted or worn contacts

• Can cause heat buildup or nuisance tripping

• Often discovered during infrared inspections

3. Mechanical Wear

• Stiff handles (often due to dried up lubricants)

• Inconsistent trip behavior

• A sign the breaker is at end-of-life

4. Environmental Damage

• Moisture intrusion (often due to the panel cover being opened or removed and not replaced)

• Dust or contamination (excessive dust, insects, and debris can enter the breaker, especially when the panel cover is off)

• Excessive heat (such as summer conditions in Phoenix) can dry out internal lubrication over time

• Common in agricultural or outdoor-adjacent installations

5. Loose Connections

• Lug terminals loosen due to conductor expansion and contraction over time (especially with aluminum wire)

• ¼-20 nuts (7/16″ hex-head) loosen due to repeated heating and cooling cycles

Most failures are age-related — not design flaws.

Why 200 Amps Made Sense (and Still Does)

The 200 amp rating wasn’t arbitrary. It provided:

• Enough capacity for full residential services

• Headroom for light commercial loads

• A practical balance between conductor size and cost

That’s why 200A mains became the standard — and why so many legacy systems are built around them.

Replacement vs Upgrade: The Real Decision

Replacing a Q2M2200MT isn’t about chasing newer technology. It’s about keeping an existing system:

• Safe

• Compliant

• Operational

For many owners and facility managers, maintaining the original panel with a compatible breaker is the most practical choice.

Why Breakers Like the Q2M2200MT Matter Today

Breakers like the Q2M2200MT are a reminder that a lot of electrical infrastructure was built to last — and did.

Understanding these legacy components isn’t about resisting progress. It’s about making informed decisions when modern replacements don’t make sense for the building, budget, or timeline.

That’s why properly tested surplus and refurbished breakers remain an important part of keeping older systems running safely.

For those operating in harsh or high-temperature environments — such as Phoenix, Arizona — it’s crucial to pair reliable breakers with proper panel maintenance. (See our article on The Importance of Regular Electrical Panel Maintenance in Arizona’s Harsh Climate for more detail.)

Installation Tips

While installation should always be handled by licensed professionals, here are some key considerations:

• Verify Panel Compatibility
  Ensure the loadcenter or panelboard is listed to accept Q2 series breakers.

• Torque Specifications
  Use a torque wrench to tighten terminals per manufacturer specifications. (250 in-lbs for the lug terminals, and 75 in-lbs for the ¼-20” nuts on the studs). Loose connections lead to heat buildup and nuisance tripping.

• Proper Wire Gauge
  Match conductor size to breaker capacity. For 200 amps, this is typically 3/0 AWG copper or 250 kcmil aluminum.

• Ambient Temperature
  Consider derating in high-temperature installations. Breakers may trip prematurely if ambient conditions aren’t accounted for.

For professionals looking to go beyond manufacturer specifications, forums like ElectricianTalk.com offer experience-based insight. Electricians working in residential, commercial, agricultural, and light industrial environments frequently discuss real-world behavior of breakers like the Q2M2200MT, including installation challenges and long-term performance.

References & Further Reading

• National Electrical Code (NEC) 2023

• UL 489 – Standard for Molded-Case Circuit Breakers

• Electrical Construction & Maintenance Magazine

• IEEE Standards for Circuit Protection

• The Importance of Regular Electrical Panel Maintenance in Arizona’s Harsh Climate