Square D Miniature Circuit Breakers
Square D by Schneider Electric has created four different lines of miniature circuit breakers for residential and industrial circuit protection. They are: lighting panelboard miniature circuit breakers, Homeline miniature circuit breakers, QO and QOB miniature circuit breakers and QOU unit mount circuit breakers.
A special feature provided by most of Square D miniature circuit breakers is the VISI-TRIP indication. When the circuit breaker has tripped, the handle moves to the center position and the red VISI-TRIP indicator appears in a window in the circuit breaker case. Trip indication immediately provides a visual indication that the circuit breaker has been tripped and interrupted the circuit.
Lighting panelboard miniature circuit breakers are designed to be used with the NF series lighting panelboards. NF lighting panelboards are used for commercial and industrial lighting and electrical distribution. Lighting panelboard miniature circuit breakers have current ratings from 15 to 125 Amps.
More Information about Square D Miniature Circuit Breakers
Homeline miniature circuit breakers are designed for fast installation and superior circuit protection. They have a full range of amperages, poles and advanced function devices that offer Arc Fault, Combination Arc Fault (CAFI), Ground Fault (Class A, GFCI) and Dual Function (CAFI and GFCI) protection.
QO and QOB miniature circuit breakers come in a complete range of amperages and interrupting ranges to fit into various QO distribution panels. Plug-on QO circuit breakers are used in NQ panelboards, QO load centers or Speed-D switchboard distribution panels. Bolt-on QOB are used in NQOD panelboards.
QOU unit mount circuit breakers are used for overcurrent protection and switching on both AC and DC electrical systems. They are available for flush, surface or DIN rail mounted applications in one, two or three pole constructions.
Trip Curve Basics Part 1
There are two critical elements in miniature circuit beakers.
Bimetal strip
This strip has two dissimilar metals attached to one another. When a prolonged overcurrent occurs, these metals begin to bend. Because the metals are different, the rate at which they bend is different, therefore causing the strip to bend. If this bending occurs long enough, the bending strip will disrupt the electrical contacts inside the breaker, causing it to trip.
Coil or solenoid
The coil or solenoid is designed for larger overcurrent events like a short circuit or lightning strike. When a large overcurrent event occurs, the plunger in the solenoid is actuated, thereby tripping the breaker.
What is a trip curve?
It is both the prolonged overcurrent protection from the bimetal strip and the higher spikes in voltage and current protection from the solenoid that make up the circuit breakers trip curve. How fast or slow these events occur determines the shape of the curve. A trip curve is simply a graphical representation of the expected behavior of a circuit protection device, in this case, a circuit breaker.
This graphical representation looks at two separate pieces of data to provide the information needed to understand when a particular breaker will trip. The first is time, more specifically, the time the circuit breaker experiences a certain amount of overcurrent. The second is the amount of current. In this case, how much more current is passing through the breaker than the protection device is actually rated for.