The Square D QO, QOT, QO-AFI, and QO-GFI are plug-on type one-, two- and three-pole thermal-magnetic circuit breakers provide overcurrent protection and switching on ac and dc systems. Plug-on QO circuit breakers are for use in QO load centers, NQ and NQOD panelboards, OEM mounting bases, and Speed-D® switchboard distribution panels. Square D also offers the HomeLine series which is NOT interchangeable with the QO series.

QO breakers
QOT tandem breakers
QO-AFI arc-fault interupting breakers
QO-GFI ground-fault interupting breakers
QO-CAFI combination GFCI & AFCI breakers

QO® Circuit Breakers

QO® (plug-on) one-, two- and three-pole thermal-magnetic circuit breakers provide overcurrent protection and switching on ac and dc systems. Plug-on QO circuit breakers are for use in QO loadcenters, NQ and NQOD panelboards, OEM mounting bases, and Speed-D® switchboard distribution panels.

Operating mechanism

QO circuit breakers have an overcenter, trip-free toggle mechanism with quick-make, quick- break action and positive handle indication. The tripping mechanisms in two-and three-pole circuit breakers operate such that an overcurrent on any pole of the circuit breaker will cause all poles of the circuit breaker to open simultaneously. Each pole has an individual thermal-magnetic trip element calibrated for 40°C ambient temperature.

Trip Indication

QO circuit breakers have Visi-Trip® trip indication, which provides a visual indication that the circuit breaker has tripped and interrupted the circuit. When the circuit breaker has tripped, the handle assumes a center position and the red Visi-Trip indicator appears in a window in the circuit breaker case. The Visi-Trip indicator is only visible when the circuit breaker has tripped. Trip indication immediately distinguishes the circuit from any other circuit which is merely in the on or off position. The circuit breaker can be reset by pushing the handle to OFF and then to ON.

Voltage Rating

The circuit breaker must have a voltage rating greater than, or equal to, the system voltage. When a circuit breaker clears an overcurrent, it is done in two steps. First, the current sensing system identifies the overcurrent and releases the tripping mechanism. This results in a parting of the contacts. The circuit breaker must then extinguish the voltage arc across the contacts. If the circuit breaker has the correct voltage rating, it can efficiently extinguish this voltage arc. QO and QOB circuit breakers are rated for use in the following voltage 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)


QOT Tandem Circuit Breakers

Square D QOT tandem circuit breakers are manufactured so two one-pole, thermal-magnetic circuit breakers occupy only one QO pole space. They are used in applications where circuit loading is light and/or noncontinuous, as in residential applications. QOT circuit breakers are available in 15/15 ampere, 15/20 ampere and 20/20 ampere construction.

Duplex breakers are available in a standard version for modern CTL loadcenters and non-compliant version for non-CTL loadcenters. Modern loadcenters are CTL rated and meet Section 384-15 of the National Electric Code. The use of non-CTL compliant breakers may violate code and UL Listing of certain loadcenters under certain circumstances. QOT circuit breakers have a mounting cam to limit their installation in QO load centers to only those positions having a mounting rail slot. This physically limits the total number of circuit beakers permitted in the panelboard for safe operation.

Each one-pole QOT circuit breaker provides individual switching and tripping action. Individual trip, two-pole circuit with common switching may be assembled by using a handle tie (kit QOTHT) between two adjacent QOT circuit breakers.


Square D AFI arc-fault breaker

Square D QO-AFI arc-fault circuit interrupters (AFCI) quickly detects a wide range of arc-fault conditions, recognises the nature and specific wave-form of an arc fault and trips the circuit breaker. Traditional circuit breakers and fuses are designed to detect overloads and short circuits. Arc-fault circuit breakers are designed to detect overloads, short circuits and arc faults.

An arc-fault circuit breaker opens the circuit and stops the arcing and high intensity heat before a fire is likely to ignite. It is designed with the same quick-open and Visi-Trip® features and reliability of other QO circuit breaker products, fits into most existing Square D load centers, and can generally be used as a direct replacement for a standard Square D circuit breakers. The AFCI overall size is larger than an equivalent QO circuit breaker.

Arc-fault circuit breakers:

  • Have special microprocessor-based arc identification to differentiate necessary operational arcs (associated with loads such as electric motors, switches and receptacles) from actual arc faults which can cause damage and fires.

  • Differentiate true arc faults from chopped wave-forms associated with switched-mode power supplies on electrical appliances, computers and lamp dimmers.

Square D QO GFCI breaker

Square D QO-GFI Qwik-Gard® Ground-Fault Circuit Interrupters offer a means of providing ground-fault protection for people. Qwik-Gard “people protection” ground-fault circuit interrupters are built as Class A devices in accordance with UL Standard 489 and CSA C22.2 #144 for ground-fault circuit interrupters (GFCIs). Class A devices must trip at 6 milliamperes of ground-fault current and above, and hold below 4 milliamperes of ground-fault current.

Qwik-Gard GFCIs provide the same branch circuit protection as standard QO circuit breakers. They are longer than standard QO circuit breakers, and thus require more gutter space. All QO electrical accessories except shunt trip and all QO mechanical accessories are available for QO-GFI and QOB- GFI circuit breakers.

Qwik-Gard circuit breakers are UL Listed and CSA Certified and available in both one- and two-pole constructions.

Square D CAFI combination breaker

Square D QO-CAFI combination Arc-Fault Circuit Interrupters circuit breakers combines GFCI and AFCI in one device, protecting against both Arc Faults and Ground Faults. 

The 2014 National Electrical Code (NEC®) now requires both Arc Fault and Ground Fault protection on kitchen and laundry circuits. Before the release of Dual Function Circuit Breakers, the only option to comply with this code was to pair an AFCI circuit breaker with a GFCI receptacle. The Dual Function Circuit breaker combines these two devices into one solution that provides both cost savings and less hassle in installation and maintenance.

For more information about Square D circuit breakers visit Square D's webiste.

DOWNLOAD PDF - QO & QOB Circuit Breaker Catalog