Datasheet

44 Miniature Circuit Breakers | US Catalog
Trip bar
Operating mechanism
Thermal trip unit
Current Flow During Operation
All highlighted components are energized during operation
Magnetic Trip Unit
Thermal Trip Unit
Current flow during operation
Thermal trip unit
.
Armature and plunger
Movable contact
Magnet trip unit
Magnetic trip unit
Magnetic trip unit
Armature and plunger
Movable contact
Trip bar
Operating mechanism
Thermal trip unit
Thermal trip unit
All highlighted components are energized during operation
Circuit breaker construction
Overload protection
The thermal trip unit protects against a continuous overload.
The thermal unit is comprised of a bimetal element located
behind the circuit breaker trip bar and is part of the breaker’s
current carrying path. When there is an overload, the increased
current flow heats the bimetal causing it to bend. As the bimetal
bends, it pulls the trip bar that opens the breaker’s contacts.
The time required for the bimetal to bend and trip the breaker
varies inversely with the current. Because of this, the tripping
time becomes quicker as current increases in magnitude.
Overload protection is applicable to any installation, conductor,
or component that can be subjected to low-magnitude but
long-time overcurrents. Low-magnitude, long-time overcurrents
can be dangerous because they reduce the life of the electrical
installation, conductor, and components. If left unchecked, fire
could result.
Components of a magnetic trip unit
When there is a short circuit, a high magnitude of current
passes through the coils creating a magnetic field that attracts
the movable armature towards the fixed armature. The hammer
trip is pushed against the movable contact and the contacts are
opened. The opening of the breaker’s contacts during a short
circuit is complete in .5 milli-seconds.
Thermal/Magnetic trip units definition
ABB Current Limiting Breakers use an electromechanical
(Thermal/Magnetic) trip unit to open the breaker contacts during
an overcurrent event. The thermal trip unit is temperature sensitive
and the magnetic trip unit is current sensitive. Both units act
independently and mechanically with the breaker’s trip
mechanism to open the breaker’s contacts.
Current fl ow during operation
Magnetic trip units (short circuit protection)
The magnetic trip unit protects against a short circuit. The
magnetic trip unit is comprised of an electromagnet and an
armature.