Overview of Square D QO Circuit Breaker from Schneider Electric

Just like other breakers, the square D QO breakers protect appliances from over-current and short circuits.

It controls the flow of electricity and also interrupts faulty currents that can threaten the safety of the circuit.

Circuit breakers come in different types and sizes, but they do similar work, which is circuit protection and prevention of electrical shock.

Whenever you are installing or replacing a circuit breaker, make sure you identify the right one.

Here are a series of breakers from Square D that you can buy.

square d qo breakers

Square D QO Qwik-Gard 20 Amp single-Pole GFCI Circuit Breaker

QO 100-Amp Two-Pole Circuit Breaker

Square D – 30-Amp, 120/240V, 2-Pole, GFCI, plugin mount

Schneider Electric QO260CP QO 60 Amp Two-Pole Circuit Breaker

Square D by Schneider Electric QO250CP QO 50 Amp Two-Pole Circuit Breaker

Square D QO Qwik-Gard Ground Fault Miniature Circuit Breaker; 40 Amp, 120/240 Volt AC, 2-Pole, Plug-On Mount

Square D Tandem Circuit Breaker 20/20 Amp Bulk

What is a Square D?

Square D is an American company that specializes in manufacturing circuit breakers.

Established in 1902, Square D was dealing in electrical products and equipment until 1920s, when it sold most of its business to focus on circuit breakers and safety switches.

Square D is a big name in the circuit breaker market, producing a range of commercial and residential breakers such as QO, QOT, QO-AFI, and QO-GFI.

They sold it to Schneider Electric in 1991.

What does QO on the circuit breaker mean?

The “QO” on the Square D circuit breakers means Qwik-Open. Meaning it is the fastest to open circuit breaker in use. The device opens after a full power cycle.

QO plug-on breakers come in 1-pole, two, and three pole terminals just to suit your requirements.

They are ideal for QO load centers, OEM mounting bases, NQ and NQOD panel boards, and others.

How do Square D breakers work?

The QO circuit breakers have a thermal-magnetic trip element calibrated at 40°C ambient temperature.

Whenever there is power surge in any of the poles, the trip mechanism opens, switching OFF the current.

Voltage rating

The voltage rating of the breaker must be higher, or equal to that of the system, for normal performance.

If the voltage rating is normal, the breaker can easily extinguish its arc whenever there is a faulty current.

The Qwik-Open “QO”and Qwik-Open-Bolted “QOB” breakers are rated for the following systems:

  • 120 Vac
  • 208/120 Vac
  • 120/240 Vac
  • 240 Vac
  • 48 Vdc (10–70 A for 1 and 2 pole circuit breakers, 10–60 A for 3 pole circuit breakers)
  • 120 Vac
  • 208/120 Vac
  • 120/240 Vac
  • 240 Vac
  • 48 Vdc (10–70 A for 1 and 2 pole circuit breakers, 10–60 A for 3 pole circuit breakers)

Key Features of a QO Circuit Breaker

  • Red Visi-Trip indicator: This breaker comes with a visual red indicator that shows when the breaker is OFF. When the breaker is OFF, the handle snaps to a midpoint position and the red visi-trip indicator appears in the breaker’s case. This feature distinguishes Square D brands from other breakers.
  • Qwik Open technology
  • Multi-purpose: This breaker not only provides overcurrent protection, it also offers arc fault protection.

Other circuit breakers from Square D

QOT Tandem Circuit Breaker

Tandem circuit breakers are known with different names such as duplex, half-height, half-inch, slimline, twin, double, and wafer breaker.

They usually look like a two-pole circuit breaker, but only connect to a single pole at the panelboard.

They are often used on residential applications with light or non-continuous circuit loading. QOT breakers are available in 15/15A, 15/20A and 20/20 ampere construction.

They are also available in standard versions for modern circuit total limiting (CTL) on load centres and non-compliant types for non-CTL load centres.

QO arc fault circuit interrupters (AFCI)

The arc fault circuit interrupters detect an arc fault and quickly opens the breaker to prevent fire outbreak.

Unlike the normal circuit breaker that detects only short circuits and overloads, AFCI detects overload, short circuit and arc-fault.

They come with a special microprocessor that differentiates true arcs from operational ones.

Once they detect the arc fault, they open the circuit.

They also come with Qwik-Open and visible trip indicator just like others.

QO Ground Fault Circuit Interruptor (GFCI)

The ground fault circuit interrupters offer protection against ground faults. They are usually installed in the bathroom, kitchen, and wet area where currents may easily come in contact with water.

The breaker shuts OFF power once it senses current leakage. They do that by comparing the inputs and output currents from electrical devices.

If there is variation between the input and output current even as little as 0.005 amps, the breaker will trip OFF.

Square D QO CAFI combination

This circuit breaker combines both AFCI and GFCI in one device there by protecting against arc and ground fault.

Before 2014, when the National Electrical Code (NEC) recommended the use of dual circuit breakers, AFCI and GFCI usually came separately. But after the invention, the two breakers became one providing dual functions.


What is the difference between a QO and QOB breakers?

The main difference between the two is that the QO breakers have a plug-on design that enables you to plug it into the load centre. While the QOB breakers have a bolt-on design for easy installation in the load center.

How do I know if I have a QO breaker?

You can know a QO breaker by looking at the label, the breaker usually has a QO letter on it. Secondly, it is usually smaller in size and equally has a small window where you can see if it is in on or trip position unlike the Home line breakers.

How do I know which Square D breaker I need?

You can do that by determining the type of load the breaker will be protecting. This may include a cooker unit, air conditioner, lighting points, and other types of electrical appliances.

Once you know the load type, you can then determine the current rating of the breaker based on the maximum current the load can draw.

You should also consider the voltage ratting and the number of poles (single or double) required for the device.

Here is a table showing different amps of breakers, its wire gauge and where to use them.

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About mariaelectricals

Hi, I am Emmanuel Nwankwo, a commercial electrician and the founder of mariaelectricals.com. I established this blog to share my seven years of work experience in electrical installations and repairs.