Datasheet

46 Miniature Circuit Breakers | US Catalog
Circuit breaker current limitation
Current limiting definitions
All ABB miniature circuit breakers are UL tested and certified as
current limiting protective devices. Current limiting circuit breakers
provide a higher level of circuit protection than typical zero point
external breakers.
UL AC 60 Hz cycle
UL defines an AC cycle as the potential energy of the wave form
traveling from zero-to-positive amplitude, positive-to-zero
amplitude, zero-to-negative amplitude, negative-to-zero
amplitude 60 times in one second. One cycle is completed
every 16.6 milliseconds.
UL breaker current limiting
UL defines breaker current limitation as a breaker that interrupts
and isolates a fault in less than ½ of an AC cycle. ½ a cycle is
completed in 8.3 milliseconds.
NEC240.2 current limiting
A device that, when interrupting current in its current-limiting
range, reduces the current flowing in the faulted circuit to a
magnitude substantially less than that obtainable in the same
circuit if the device were replaced with a solid conductor having
comparable impedance.
IEC 60947-2 current limiting circuit breaker
A circuit breaker with sufficiently short trip time to prevent the
short-circuit current from reaching the peak value which would
otherwise be reached.
ABB current limiting breakers
ABB current limiting breakers can interrupt and isolate a fault in
 of an AC cycle. The breaker fault interruption is completed in
2.3 to 2.5 milliseconds.
Zero point extinguishing breakers
A typical zero point extinguishing breaker interrupts a fault and
does not isolate the energy. The breaker allows an arc to be
present between the open contacts until the AC wave form
crosses zero. When the wave form crosses zero, the potential
energy is zero and the arc (fault) naturally extinguishes. The arc
could be present for up to 8.3 milliseconds.
Current limiting breakers and electrical networks
Current Limitation
When a short-circuit condition occurs, the “ideal” current limiting
circuit breaker opens before the current waveform can reach its
full potential magnitude which occurs at ¼ cycle (4.17ms). ABB’s
current limiting breakers can interrupt a fault in about ½ cycle or
2.3 ms to 2.5 ms. ABB’s current limiting breakers interrupt a short
circuit in less than  cycle and limit the amount of current that
can reach a circuit. Limiting the available current on the circuit
provides additional protection against network, breaker, or bus
damage and prevents the tripping of upstream breakers (selective
coordination).
I
2
t
The true destructive nature of a short circuit is measured by the
time it is available combined with the peak value of the short
circuit. The IsqT (Amps Squared over Time) value represents the
amount of energy available on a network during a short circuit
and is represented by the shaded area on the graph below.
During a short circuit, both magnetic forces and thermal energy
combine to damage devices on the electrical network. The level
of thermal energy and magnetic forces are directly proportional
to the square of the current. The magnetic forces vary as a
square of the peak current available and the thermal energy varies
as a square of the RMS (root mean square) current available.
ABB’s current limiting breakers will limit the let-through energy
to a fraction (⁄) of the value that is available from the
network. By comparison, a zero crossing breaker would let
through approximately 100 times as much destructive energy
as the current limiting circuit breaker [ (100,000A / 10,000A)
squared – 100X]. ABB’s current limiting breakers limit the short
circuit current to a relatively small magnitude in an extremely
short time, which dramatically limits a short circuit’s destructive
energy.