UL solutions from Bihl+Wiedemann

USA and Canada – a Specific Market

North American equipment manufacturers who make products for the domestic market must comply with local regulations that are fundamentally different from European IEC standards. The same applies, of course, to manufacturers from other countries who wish to export equipment to this market. In practice, it is essential that the equipment is UL-certified. Special care must often be taken to comply with the power limitation associated with NEC Class 2/limited energy circuit.


Bihl+Wiedemann’s advanced ASi solutions consisting of ASi-5/ASi-3 gateways and 30 V power supplies are all UL-certified. Further, we offer special NEC Class 2 power supplies and UL-certified power limitation modules which also satisfy NEC Class 2 requirements on limited energy circuits.

UL Certification & 100 W Power Limit


Anyone exporting electrical products to North America, or manufacturing them there for the domestic market, must comply with the rules set out in the NEC, among others. For instance, conformity with the safety regulations of the USA and Canada is confirmed by the UL test mark issued by the “Underwriter Laboratories” testing laboratory. References to UL standards are found in the U.S. National Electrical Code (NEC). Many components, such as typical sensors, are certified as Class 2 only, which means that their power supply must not exceed 100 W. This limitation to 100 W must be tested and certified by UL (or a comparable body) in accordance with the standards. Three options are equally available for this purpose:


  1. Limited energy circuit according to UL/CSA 61010-2-201
  2. Limited Power Source according to UL/CSA 60950-1
  3. Class 2 supply source according to NEC, NFPA 70, Clause 725.121 and CEC, Part I, C22.1.


What Does This Imply for the ASi Installation?

Since ASi-connected sensors are mostly only permitted for use in NEC Class 2 circuits (limited energy circuits), care must be taken to ensure that the power limitation is maintained in accordance with the standard. Bihl+Wiedemann offers two options for this: Either a separate NEC Class 2-certified power supply for each ASi circuit or a heavy-duty power supply in combination with a UL-certified power limitation module (see setup recommendations). Our power limitation module was specially developed for ASi-5/ASi-3. An important aspect, which had special attention during the development, was to make sure that communication on ASi would not be negatively affected by the power limitation module.

Advantages of UL-Compliant Implementation With Bihl+Wiedemann

Compliance With Standards

All ASi-5/ASi-3 gateways are either UL-certified or are in the process of being so. To comply with the 100 W limitation for each ASi circuit in a UL-compliant manner, it is possible to use either the 2-channel power limitation module (BWU4189) or the NEC Class 2 power supply (BW4223). Both are also UL-certified and ensure that ASi-3 and ASi-5 communications continue to function properly.

Advanced Diagnostics

Our ASi-5/ASi-3 gateways enable you to permanently monitor the current and voltage of the power supply of your ASi installation. The OPC UA server of the gateway also enables seamless connection to cloud services, for example for predictive maintenance.

Reduced Costs

The 30 V power supplies are less costly than previous ASi power supplies – mainly because data decoupling is now integrated as standard in our ASi-5/ASi-3 gateways. This means that a separate decoupling is automatically available for each ASi circuit and one power supply unit can simultaneously supply several ASi circuits. This also means that you don't have to use separate circuit breakers for each ASi circuit.

Smaller Footprint

Further the power supplies are also more compact compared to special ASi power supplies, as they no longer contain decoupling coils. They can be connected side-by-side, which means that they do not require any free space on the left and right. This frees up additional valuable space in the control cabinet.

Setup Recommendations for North America

Small Applications With Just 1 ASi Circuit

  • 30 V power supply is limited to 100 W, UL-certified, NEC Class 2
  • No power limitation module necessary
  • Simple setup for small applications
  • A total of 100 W is available for the ASi nodes

Application With 2 ASi Circuits


Scenario 1:

More than 1 ASi circuit is required and a separate 100 W power supply is to be used for each ASi circuit. Then it is recommended to use a gateway with 2 ASi circuits and integrated decoupling optimized for 2 limited energy circuits.

  • 2 × 30 V power supplies are each limited to 100 W, UL-certified, limited energy circuit
  • Setup without power limitation module
  • Gateways optimized for 2 × UL-compliant ASi circuits limited to 100 W. Available for different fieldbuses (EtherNet/IP, BWU3947, PROFINET, BWU3830)
  • A total of 200 W is available for the ASi nodes

Scenario 2:

A common power supply is to be used for 2 ASi circuits (double master). In that case, to create a UL-compliant 100 W limited ASi circuit, it is recommended to use the power limitation module. One advantage of this variant is flexibility: Machines can be built the same way as usual and for the North American market one simply adds the power limitation module. In addition, the power limitation module enables the implementation of large applications with increased current requirements from ASi (see the final setup recommendation).

  • ASi-5/ASi-3 gateway is not limited to 100 W according to UL
  • A low cost 30 V 8 A power supply (optional BW4219: 1-phase or BW4220: 3-phase) for both ASi circuits
  • Limited energy circuit limitation achievable with the power limitation module (BWU4189): 2 channels in one IP20 housing for 2 separate ASi circuits
  • A total of 200 W is available for the ASi nodes

Large Application With More than 1 ASi Circuit and High Current Demand From AS

If a total of 200 W is not sufficient to supply the ASi nodes, it is possible to use one power limitation module per ASi circuit. Thus, the two ASi circuits can each be split into two separate 100 W sections. Up to a total of 400 W is then available for the ASi nodes of the two ASi circuits.

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ASi - Una tecnologia che fa risparmiare risorse

L'impegno di cablaggio notevolmente ridotto con AS-Interface consente di risparmiare sui costi di montaggio e sui materiali. In questo modo si risparmiano risorse preziose.


Per saperne di più!

  • ASi-5/ASi-3 gateway with 2 × 8 A decoupling is not limited to 100 W according to UL
  • A low cost 30 V 16 A power supply (optional BW4221: 1-phase or BW4222: 3-phase) for both ASi circuits
  • Limited energy circuit limitation achievable with 2 power limitation modules (BWU4189): 2 channels in one IP20 housing for 2 sub-circuits of one ASi circuit
  • A total of 400 W is available for the ASi nodes

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