Overview of Square D QO Circuit Breaker from Schneider Electric

When it comes to electrical circuit protection, the square D QO breakers have always been the best. The breaker protects electrical appliances from overload and short circuits.

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

If you are looking for a quality circuit breaker to protect your home and appliances, I recommend you go for QO breakers.

What is a square D QO breaker?

A square D QO breaker is a “Qwik-Open” breaker from Schneider Electric. It is the fastest opening circuit breaker in the industry, and opens within one complete 60 Hz power cycle (1/60th of a second).

Benefits of using QO breakers.

Using square d qo circuit breakers comes with lots of benefits such as:

Safety: The primary role of a breaker is to protect the circuit and appliances from overload and short circuits.

High-quality breakers are built to stringent safety standards that can enable them to interrupt faulty currents and prevent electrical hazards.

Circuit protection: Breakers play a huge role in safeguarding electrical circuits. They can detect and quickly cut off the flow of abnormal currents to protect the circuit and appliances.

Durable and reliable: High quality breakers are built with robust materials and advanced technologies, which makes them strong and reliable.

Compatible: High quality breakers are built to meet residential and industrial standards, ensuring compatibility with various electrical systems and equipment.

Types of square D QO breakers

There are different types of qo breakers, they include:

Standard qo breakers

This is the type of circuit breakers we use in our homes and industries for short circuit and overload protection.

They are available in single pole for 120-volt circuit, double pole for 240 volts circuit and triple poles for three phase 240-volts.

Standard qo breakers are available in various amp rating starting from 15 to about 200 amps.

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 GFCI (ground fault circuit interrupter) breaker

This is a breaker used to prevent electrical shock that may arise due to ground faults. It is available in 15, 20 and 30 amps rating and are mostly installed in kitchen, bathroom and other wet areas within the house.

See how to install a gfci outlet in your kitchen and bathroom

QO-AFCI (arc fault circuit interrupter) breakers

The afcis 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.

AFCIs are available in 15 and 20 amps rating, and are required in certain areas of the homes such as bedrooms and living rooms.

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.

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

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

How the Square D QO breakers work

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

Whenever there is an over current 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 square D QO Breakers

Plug-on design

The qo breakers come with a plug on design for easy installation or replacement. If you want to install the breaker, all you can do is to plug it into the load center or panel. No need for wiring.

Visi-trip indicator

Square D QO breakers come with a Visi-Trip indicator, a red window that displays a trip sign when the breaker is off. This feature helps to easily identify the breaker that has tripped off.

Dual function capability

Some models of the QO series combine both the features of a circuit breaker and a ground fault circuit interrupter (GFCI) or an arc fault circuit interrupter (AFCI) in a single device. This integration improves safety by providing protection against both ground faults and arc faults.

High quality and Reliable

Square D breakers are known for their superior quality and reliable. They are designed to provide safe and efficient circuit protection for both residential, commercial, and industrial applications.

Wide Range of Options

The QO series offers a wide range of circuit breakers to meet various needs. They are available in different ampere ratings, ranging from 15 to 125 amps, allowing for the protection of circuits with different power requirements.


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 and equally has a visi-trip indicator to show if it is in ON or OFF.

How do I know which Square D breaker I need?

You can know the breaker you need by determining the type of load the breaker will be protecting. This may include cooker unit, air conditioning, lighting 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 rating and the number of poles (single or double) required for the device.  

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.

About mariaelectricals

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