The Electronic Circuit Protector (ECP) is a solid-state current interrupter. Instead of using a traditional electromagnetic contact mechanism, the protector uses a power semiconductor plus electronic control circuitry to provide responsive current limiting and current interrupting functionality. The E-T-A ESX10-TB-114-DC24V-0.5A-E as shown in Figure 1 is a representative example. This advanced device is rated for 0.5 A and features remote on/off control as well as a PNP output to indicate status. These added features allow the ECP to be tightly coupled to a Programmable Logic Controller (PLC) allowing on-off control, monitoring, and reset.
Figure 1: Image of an E-T-A ESX10-T series circuit breaker with a green LED indicating a healthy status.
Tech Tip: Technically, the featured device is an Electronic Circuit Protector (ECP). However, it is commonly identified as an Electronic Circuit Breaker (ECB).
Occasionally, these devices are called solid-state over-current switches. This is true when we consider the UL E322549 listing where we find the featured device under the NKCR category.
What are the advantages of an electronic circuit protector?
The ECP provides fast response with controlled current limiting along with remote status monitoring and control. This provides tight integration with PLC-based systems.
Constant (controlled) current advantages
Recall that the ECP features a solid-state (likely MOSFET) pass element. This power semiconductor and electronic control circuitry operate to limit the output current. As an analogy, we could view an ECP based system as a bench-type power supply:
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The system operates in Constant Voltage (CV) mode most of the time.
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If the current reaches the “trip” point, the system transitions to a Constant Current (CC) mode.
Unlike the power supply, the ECP features a clock-like mechanism that will track the time spent in an overloaded condition. After the time has expired, the ECP will toggle to a fault condition.
Understanding ECP trip curves
The ECP system’s CV and CC modes are reflected in the trip curves as shown in Figure 2 (left). Notice that the featured ECP is current limited to 1.8 x the nominal current rating (0.9 A for the featured breaker). This is truly a CC mode, as the pass element operates in its linear region.
As a counterexample, consider the curve for a conventional electro-mechanical circuit breaker such as the E-T-A Type 2210-T2. The circled red portion of Figure 2 (right) shows momentary uncontrolled current for a brief period of time. This reflects the time it takes for the breaker’s current detecting solenoid to activate. We observe that the ECP (left) does not have this uncontrolled high-current plateau. Instead, the pass element and associated electronics clamp the current to 1.8 times the breaker’s nominal current rating.
Figure 2: Trip curve comparison between an electronic and a thermal-magnetic circuit breaker.
Tech Tip: The pass element dissipates a large amount of heat when operating in the linear region. The short overcurrent period prevents overheating. However, we must follow the datasheet specification and derate the ECP:
Note: When mounted side-by-side without convection, the devices can only carry max. 80 % of their rated current continuously (100 % ON duty) due to the thermal effect.
ECP remote control and reset functionality advantages
The featured circuit breaker includes remote on-off control. To operate (turn on), 24 VDC must be applied to terminal 21 as shown in Figures 3 and 4. Many different sourcing options are available. This is a perfect opportunity for PLC control of the breaker. In this application, the ECP performs double duty, acting as both overcurrent protector and SPST contactor (relay).
Note that the ECP may be reset via the remote-control line. Pulling the line low, followed by reassertion of 24 VDC will reset the protector.
Figure 3: Side view of the E-T-A ESX10-T ECP.
Figure 4: Top view of the E-T-A ESX10-T ECP.
ECP health monitoring advantages
The health status of the ECP is prominently displayed on the multicolor LED as shown in Figure 1:
- Green = on and operating normally
- Orange = overload
- Red = tripped or turned off
The health status is also echoed on output pin 23. This is a PNP output where the ECP’s green is assigned an active-high signal. Once again, this facilitates tight PLC coupling. The PLC can monitor this line to detect a malfunction. It can then take appropriate action to alert the operator, activate backup systems, or perform an orderly shutdown.
Enhanced ECP to PLC advantages
While not featured in this ECP, E-T-A offers advanced monitoring capability. Their top-of-the-line devices offer network capability via Modbus and even IO-Link. These devices allow the PLC to monitor parameters such as real-time current, system voltage, minimum, maximum, and peak current. These may provide valuable troubleshooting information to the technician if properly integrated into a larger SCADA system.
Panel size advantages
The featured ECP was designed to operate side by side with other members of the family. This results in a compact DIN rail-saving construction. In Figures 1 and 4 we can see the slots to accommodate busbar which reduce the number of wires leading to the ECP.
Parting thoughts
This engineering brief provides an introduction to the ECP by studying a representative E-T-A device. The remote control and health status lines provide an opportunity for tight PLC integration. We can improve the performance by shifting to advanced networking and monitoring capabilities available via Modbus and IO-Link.
In all cases, you, the panel designer must select the product to match the desired capabilities and integration level appropriate to your control panel.
We would love to hear from you. How have you used ECPs to enhance your industrial control 24 VDC power and distribution systems?
Best wishes,
APDahlen
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About this author
Aaron Dahlen, LCDR USCG (Ret.), serves as an application engineer at DigiKey. He has a unique electronics and automation foundation built over a 27-year military career as a technician and engineer which was further enhanced by 12 years of teaching (interwoven). With an MSEE degree from Minnesota State University, Mankato, Dahlen has taught in an ABET-accredited EE program, served as the program coordinator for an EET program, and taught component-level repair to military electronics technicians. Dahlen has returned to his Northern Minnesota home and thoroughly enjoys researching and writing articles such as this.