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Rethinking 24 Volt Circuit Protection

 12 January 2022

Dynamic? Absolutely!

Reliable circuit protection of the 24 volt power supply is essential for trouble-free operation of systems and machines. Whether they consist of sensitive loads like controllers, critical safety devices or robust electromechanical components, they need to be protected from the effects of short circuits and overloads. Where once classic circuit breakers were used, electronic fuses now ensure safety and provide additional benefits. The electronic circuit protection of the future will even go one step further: It will be dynamic!

The Benefits for You:

  • Dynamic, automated adaptation of the tripping current to the current load situation
  • Reliable tripping in the event of faults
  • Power supply overdimensioning can be avoided

As the level of automation in production and process systems increases, the number of loads powered by 24 volt direct current – controllers, sensors and electric motors – also continues to increase. The current in these circuits is usually provided by power supply units. Power supply units cut the power when a nominal value is exceeded and connected loads fail; therefore, circuit breakers protect individual components or groups of components in order to limit the effects of overcurrents and short circuits. However, conventional automatic thermal-magnetic circuit breakers require a high overcurrent to reliably trip. The necessary cut-off current may even be greater than the maximum current provided by the power supply. That makes fast, reliable shut-down in the event of short circuit impossible. In addition, capacitive loads, long cables or the simultaneous start-up of several 24 volt loads may cause additional challenges for the power supply and fusing.

An Electronic Circuit Breaker That Can Do Everything?

Electronic circuit breakers (ECBs), which use semiconductors as switching components and continuously measure the current, respond to changes in current values with much greater sensitivity. These circuit breakers react as soon as the output current exceeds the nominal current value, which is configurable. The tripping time depends on the magnitude of the overcurrent. A microprocessor handles the processing and calculation of the tripping time and is responsible for tripping the semiconductor switch. This can switch off precisely and quickly when secondary-side overcurrents occur. Electronic circuit breakers are also able to switch the power off at or above a specified value – for example, 1.3 or 1.5 times the nominal current – within a specified period of time. When capacitive loads are applied, current spikes are handled without interruption. More sensitive response behavior like this, along with the active current limitation, also allows electronic circuit breakers to be used with greater maximum cable lengths.

Last but not least, this type of circuit protection offers a substantial benefit for the dimensioning of the power supply. In contrast to conventional circuit breakers, a smaller buffer in the output load dimensioning suffices for the maximum overload range of the power supply. For example, the constant current mode or Power Boost behavior represents one element of the overload behavior. Because traditional circuit breakers require high overcurrents for them to trip in the event of a short circuit, their power supplies require corresponding overdimensioning. With the Pro 2 Power Supply, that’s not necessary. “The overall power requirements may, under certain circumstances, be several times the current required for normal operation,” explains Frank Sellke, Business Development Manager for Interconnection and Interface Products at WAGO. “This overdimensioning incurs costs, and beyond that, it requires more space in the control cabinet.”

Intelligent Load Management Becomes Dynamic

The WAGO Pro 2 Power supply combines the features and benefits of ECBs with communication capability and simple, versatile device parameterization. With the attachable communication module, the Pro 2 Power Supply can provide information about current data, such as base loads or peak loads, at any time via standardized protocols. In addition, the configuration of the power supply can be modified within milliseconds, even during ongoing operation. Parameters like overload behavior, output voltage and the tripping value for the ECB function can adjusted.

In connection with a controller, this opens up completely new possibilities: dynamic protection of load circuits! The way it works is both simple and ingenious: If multiple loads are attached to one load circuit, the different capacitive and inductive loads cause significant current fluctuations during start-up and shut-off operations. Even with ECBs, the only way to handle this is with overdimensioning and staggered switching times. “That’s not the case with the Pro 2 Thanks to its communication features, the characteristic value for the circuit protection can be automatically adjusted to the present current load,” explains Florian Kothe, Business Development Manager for Interface Products at WAGO. “The PLC, which controls the on and off switching of the loads, informs the power supply of the load value to be expected in the next 20 milliseconds. The value is adjusted accordingly with a configurable buffer of 3 to 5 %.“ The result is circuit protection that functions safely and reliably at every operating point – without overdimensioning!