Normally Closed Current Sensors

Occasionally a customer will call our Technical Support to ask if we offer any Normally Closed (N/C) current sensors. While it is true that all of our self-powered AC current sensors only offer a Normally Open (N/O) Solid State contact, we do carry several relay & AC sensor combinations that can be configured to function as powered N/C current sensors. Specifically, those models are the RIBXLCRA & RIBXLCRF, RIBXLCJA & RIBXLCJF, RIBXLSRA & RIBXLSRF, and RIBXLSJA & RIBXLSJF.

Each of the above models comes in a 4″ by 4″ plastic enclosure and contains either a solid core or split core remote current sensor. When wired as shown in Fig. 1, the device will function as a current sensor with a SPDT relay output.

Fig. 1

How it Works:

When current through the load wire exceeds the threshold (see datasheet) of the device, the sensor feedback contact will close. This will allow the voltage connected to the upper screw terminal to reach the on-board relay coil. Once the relay coil is energized, the N/O relay contact will close and the N/C relay contact will open.

Fig. 1 most closely represents the RIBXLCRA & RIBXLCRF, but all other models would be wired similarly. The relay output of the RIBXLSRA & RIBXLSRF and RIBXLSJA & RIBXLSJF is slightly different, as it is only a SPST that is selectable between N/O and N/C, and those models also have an override switch built it.

If you have any questions about this blog or any of our products, please feel free to call or email our Technical Support, and we will be glad to help.

About the Author

Henry Smith is a 34-year-old engineer at Functional Devices, Inc. He has a BSEET obtained from Purdue University in 2014 and a lifelong interest in electronics. As an engineer at Functional Devices, he gets to provide Technical Support to our customers, from distributors to specifying engineers and installers.

Henry enjoys providing tech support, as it allows our company to assist at every level of our product’s lifecycle and exposes us to interesting and unique applications. While not every technical question is unique, even answering a simple question or providing someone with the information in a timely manner can go a long way to helping him or her meet a deadline.