Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
IEC PAS 63023: Switchgear — Input/Output Devices for Industrial Automation
Technical specifications for modular I/O devices integrated with low-voltage switchgear in industrial automation environments
1. Scope and Context of IEC PAS 63023
IEC PAS 63023 addresses a convergence point between low-voltage switchgear and industrial automation: input/output (I/O) devices that are physically and functionally integrated into switchgear assemblies. Traditionally, switchgear (IEC 61439 series) and automation I/O (IEC 61131-2) have been treated as separate domains. The PAS bridges this gap by specifying the requirements for I/O devices that operate within switchgear enclosures, sharing the same busbar systems, power distribution, and environmental conditions as power switching and protection components.
As a Publicly Available Specification (PAS), 63023 represents a pre-standard that responds to industry demand for greater integration between the power distribution layer and the control layer. In modern industrial facilities, motor control centres (MCCs) and distribution boards increasingly incorporate digital I/O for monitoring contactor status, measuring current, and controlling remote actuators. The PAS provides a common framework for these hybrid devices.
IEC PAS 63023 is particularly relevant for Industry 4.0 / IIoT deployments where distributed I/O at the switchgear level reduces cable runs, simplifies commissioning, and enables predictive maintenance by capturing data directly at the power distribution point.
2. Technical Requirements and Device Classification
2.1 I/O Signal Types and Ratings
The PAS defines five categories of I/O signals for switchgear-integrated devices:
| Category | Signal Type | Typical Rating | Application Example |
|---|---|---|---|
| Digital Input (DI) | 24 V DC, sink/source | 3 ms filter, 0.5 A max | Contactor auxiliary contact status |
| Digital Output (DO) | 24 V DC, 230 V AC | 0.5 A DC / 2 A AC | Contactor coil energisation |
| Analogue Input (AI) | 4–20 mA, 0–10 V | 16-bit resolution, ±0.1 % FS | Motor current transformer (CT) feedback |
| Analogue Output (AO) | 4–20 mA | 16-bit, ±0.2 % FS | Variable frequency drive speed setpoint |
| Temperature Input (TI) | PT100/PT1000, thermocouple | ±0.5 °C accuracy | Busbar temperature monitoring |
A critical requirement is that all I/O devices must maintain their rated accuracy and functionality within the switchgear ambient temperature range of −5 °C to +55 °C (class 3K5 per IEC 60721-3-3). This requires careful thermal design because switchgear enclosures can experience internal temperature rises of 15 K above ambient due to ohmic heating from busbars and power components.
A common failure mode in switchgear-integrated I/O devices is thermal drift of analogue inputs. The PAS warns that 4–20 mA loop-powered devices are particularly susceptible: the internal reference voltage of many commercially available ADC modules drifts by 50–100 ppm/°C, leading to measurement errors of up to 2 % at 55 °C ambient. Designers should specify < 25 ppm/°C reference drift or implement software compensation using an on-board temperature sensor.
2.2 Fieldbus Integration and Communication
The PAS does not mandate a specific fieldbus protocol. Instead, it requires that the I/O device support at least one of the industrial communication profiles listed in IEC 61784-1 (which includes PROFIBUS, PROFINET, EtherNet/IP, EtherCAT, and Modbus TCP). The device shall present a standardised device profile (IEC 62390) that allows a PLC or DCS to discover its I/O configuration automatically — reducing engineering effort during commissioning and replacement.
3. Engineering Design Insights for Switchgear I/O Integration
Several design considerations emerge from the PAS that directly impact reliability and safety:
Galvanic isolation. I/O channels connected to switchgear compartments (where voltages up to 690 V AC may be present) must provide reinforced insulation rated for 2.5 kV AC, 1 minute. The PAS recommends optocouplers or digital isolators with ≥ 8 mm creepage distance for DI/DO channels, and isolated sigma-delta modulators for AI channels. Non-isolated designs are only permitted for I/O within the same functional compartment and sharing the same ground reference.
Surge immunity. Switchgear environments are electrically noisy. The PAS mandates that I/O devices comply with IEC 61000-4-4 (electrical fast transient) at Level 4 (4 kV coupling, 2 kV direct) and IEC 61000-4-5 (surge) at Level 3 (2 kV line-to-earth, 1 kV line-to-line). Achieving this requires careful PCB layout with transient suppression diodes on every external connection and RC snubbers on DO channels driving inductive loads (contactors, relays).
A practical recommendation from the PAS annex: implement “I/O health monitoring” — each I/O module should continuously measure its internal temperature, supply voltage, and communication error rate. These metrics can be read over the fieldbus and used for predictive maintenance. A gradual increase in communication error rate (e.g. from 10⁻⁹ to 10⁻⁶ BER) often precedes a connector oxidation or cable degradation failure by weeks.
4. Frequently Asked Questions
Q1: Can conventional PLC remote I/O modules be used inside switchgear, or is IEC PAS 63023-specific hardware required?
A: Conventional industrial I/O modules can be used, but they may not meet the thermal, EMC, and creepage requirements specific to the switchgear internal environment. The PAS is intended for devices designed and tested for this specific use case. Many manufacturers now offer “switchgear-rated” I/O modules that comply with both IEC 61131-2 and IEC PAS 63023.
A: Conventional industrial I/O modules can be used, but they may not meet the thermal, EMC, and creepage requirements specific to the switchgear internal environment. The PAS is intended for devices designed and tested for this specific use case. Many manufacturers now offer “switchgear-rated” I/O modules that comply with both IEC 61131-2 and IEC PAS 63023.
Q2: How does the PAS address SIL (Safety Integrity Level) requirements for I/O used in safety functions?
A: The PAS acknowledges that I/O devices may be used in safety-related applications. In such cases, the device must comply with IEC 61508 (functional safety) and the relevant sector-specific standard (e.g. IEC 62061 for machinery). The PAS references the required diagnostic coverage (DC ≥ 90 % for SIL 2) but defers detailed safety design to IEC 61508.
A: The PAS acknowledges that I/O devices may be used in safety-related applications. In such cases, the device must comply with IEC 61508 (functional safety) and the relevant sector-specific standard (e.g. IEC 62061 for machinery). The PAS references the required diagnostic coverage (DC ≥ 90 % for SIL 2) but defers detailed safety design to IEC 61508.
Q3: What is the maximum number of I/O points per switchgear section?
A: The PAS does not set a hard limit, but notes practical constraints: each I/O module generates heat (typically 2–5 W per 8-channel module), and the cumulative temperature rise must stay within the −5 °C to +55 °C ambient rating. A typical 600 mm wide section can accommodate 4–8 modules (32–64 I/O points) before thermal derating becomes necessary.
A: The PAS does not set a hard limit, but notes practical constraints: each I/O module generates heat (typically 2–5 W per 8-channel module), and the cumulative temperature rise must stay within the −5 °C to +55 °C ambient rating. A typical 600 mm wide section can accommodate 4–8 modules (32–64 I/O points) before thermal derating becomes necessary.
Q4: Are there specific wiring requirements for I/O within switchgear?
A: Yes. I/O wiring must be segregated from power cabling by at least 50 mm (or by a grounded metal partition). The PAS refers to IEC 60364-5-52 for cable sizing and IEC 61439-1 for internal separation requirements. Shielded twisted-pair cable is mandatory for analogue and communication signals.
A: Yes. I/O wiring must be segregated from power cabling by at least 50 mm (or by a grounded metal partition). The PAS refers to IEC 60364-5-52 for cable sizing and IEC 61439-1 for internal separation requirements. Shielded twisted-pair cable is mandatory for analogue and communication signals.
