Datasheet

US Catalog | Miniature Circuit Breakers 45
Circuit breaker construction
Arc runner
Arc chute
Magnetic Trip Unit
(Region Two)
Thermal Trip Unit
(Region One)
Moving Contacts
(Region Three)
Arc runner Arc chute
Arc runners/arc chutes
The arc runner guides the electric arc away from the open contacts
into the arc chute where it is extinguished.
During an overload or short circuit event, the contacts of the
breaker separate, and an electrical arc is formed between the
contacts through air. The arc is moved into the arc chute by
“running” the arc down the interior of the breaker along the arc
runner. When the arc reaches the arc chute, it is broken into
small segmented arcs. The segmented arcs split the overall
energy level into segments less than 25 V. Each 25 V segment
does not have a high enough energy level to maintain an arc
and all energy is naturally dissipated.
Breaker curves
Thermal trip unit (region one)
The first sloping region of the breaker curve is a graphical
representation of the tripping characteristics of the thermal trip
unit. This portion of the curve is sloped due to the nature of the
thermal trip unit. The trip unit bends to trip the breaker’s trip bar
in conjunction with a rise in amperage (temperature) over time.
As the current on the circuit increases, the temperature rises,
the faster the thermal element will trip.
Example using the curve below: If you had a 10 A breaker and
the circuit was producing 30 amps of current, the breaker would
trip between two seconds and one minute. In this example, you
would find the circuit current on the bottom of the graph
(multiples of rated current). The first line is 10 amps (10 amp
breaker x a multiple of one), the second line is 20 amps (10 amp
breaker x multiple of two), and the third line is 30 amps (10 amp
breaker x multiple of three). Next, you would trace the vertical 30
A line up until it intersects the red portion of the breaker thermal
curve. If you follow the horizontal lines on both sides of the red
curve to the left, you will see that the breaker can trip as fast as
two seconds and no slower than one minute.
Magnetic trip unit (region two)
This region of the breaker curve is the instantaneous trip unit.
ABB’s miniature circuit breaker’s instantaneous trip unit interrupts
a short circuit in 2.3 to 2.5 milliseconds. Because of this, the
curve has no slope and is graphically represented as a vertical
straight line.
See curve example. If you had a 10 amp breaker, the magnetic
trip element would interrupt a short circuit between 10 and 30
amps (10 amp breaker x multiple of two and three) in 2.3 to 2.5
milliseconds.
Breaker contacts (region three)
This region of the curve is the time required for the contacts of
the breaker to begin to separate. The contacts will open in less
than .5 milliseconds and is graphically represented by the bottom
vertical portion of the curve.