Miniature Circuit Breakers MCBs

UL 489 and UL 1077 – designed for AC and DC

MCBs are essential components in electrical systems. They are designed to protect applications and electrical loads against the dangerous consequences of overcurrents.

In the following, we’ll explain in detail how the UL 1077 and UL 489 standards specify MCBs and why they are so important.

While MCBs according to UL 1077 provide additional protection for low voltage applications, the MCBs according to UL 489 are designed to provide reliable protection for a wide range of applications and voltage ranges.

Typical applications:

  • Automotive manufacturing
  • Chemical, oil and gas industry
  • Automation and building technology
  • Telecommunications and data centres

Optional add-on modules

The standard products can be expanded with different add-on modules for a customised system, perfectly adapted for your application.


The X4230-A error signalling switch for the 4230-T is equipped with a change-over switch as a signalling contact. An error message is only issued if the circuit breaker has tripped due to a fault (overload, short circuit), but not if the switch is actuated manually. The pending tripping signal can be acknowledged by pressing the reset lever on the front.


The X4230-FA is an add-on module for the 4230-T circuit breaker. The operating current breaker is designed for remote disconnection and signalling whether the circuit breaker has tripped electrically or was switched off manually.


The X4230-S auxiliary switch has a change-over contact as a signal contact and is actuated via the circuit breaker. Unlike the X4230-A, there is no differentiation between manual or electrical switch-off.

Videos: How to mount the add-on modules

Our MCB portfolio

Our thermal-magnetic MCB portfolio (4230-T) includes both UL 1077 and UL 489 versions have rated currents from 1 to 63 A with different characteristics and numbers of poles. The 4230-T...U  product group (UL 489) is suitable for circuit protection in AC or DC networks, the 4230-T...E product group (UL 1077 / EN 60947-2) is designed for additional protection.

The application example according to UL 508 shown here illustrates the wide range of applications.

The UL 508A standard specifies the requirements for the construction and installation of control panels to ensure that they comply with electrical safety standards. Among other things, the standard covers the design, wiring and operation of control panels and guarantees that they can control electrical systems safely and reliably.

Our 4230-T MCB is suitable for use in switchgear according to UL 508A. Each load can be individually protected according to the standard.

Busbars and further connection accessories

Jumpers, also called busbars, are used for electrical connections and power distribution between switchgear. You can select the correct busbars and suitable accessories, such as end caps, connection terminals and cover caps, for your application from our portfolio.