Keyence KV-RC8BXR Programmable Controller I/O Unit

The Keyence KV-RC8BXR is an I/O expansion unit designed for Keyence's KV series programmable logic controllers (e.g., KV-3000, KV-5000/7000, KV-8000). It provides 8 relay output points, each rated for 2A at 250V AC or 30V DC. The "RC" designation likely indicates relay contact output with high inrush capability. This unit connects to the main CPU via the KV expansion bus, adding discrete control capability for solenoids, contactors, pilot lights, and small motors without increasing the CPU's local I/O count.

Technical Specifications

• Model: KV-RC8BXR

• I/O Points: 8 outputs (relay)

• Output Type: Form A (NO) dry contact, common per 4 points (2 commons)

• Contact Rating: 2A per point (resistive), 1A (inductive)

• Maximum Switching Voltage: 250V AC / 30V DC

• Maximum Switching Current: 2A per common

• Minimum Load: 5V DC, 1mA

• Response Time: 10 ms typical (off->on), 10 ms (on->off)

• Mechanical Life: 20 million operations

• Electrical Life: 100,000 operations at rated load

• Internal Power Consumption: 30 mA at 5V DC from backplane

• External Power Required: None (outputs powered by load source)

• Connection: Removable terminal block (screw type, 0.2–2.5mm²)

• Dimensions: 95mm x 50mm x 60mm

Physical Design

The KV-RC8BXR is housed in a slim, modular plastic case that snaps onto a DIN rail. It connects to the previous unit (CPU or another expansion) via a locking bus connector. The front panel has eight green LEDs showing the status of each output, plus a red LED for power. The terminal block is removable without tools (lever-type spring clamp in some revisions, screw type in others). The unit is keyed to prevent incorrect connection of the bus cable.

Compatibility

This unit is compatible with all Keyence KV series CPUs that support expansion I/O, including KV-3000, KV-5000, KV-5500, KV-7000, KV-8000, and the older KV-1000/3000 series (with adapter). Up to 16 expansion units (including inputs, outputs, analog, and high-speed counters) can be connected in any order. The address assignment is automatic via the KV Studio software or by the hardware switches on the unit (if present, some models use rotary switches for starting address).

Applications

Typical applications include controlling small contactors for motor starters, actuating solenoid valves, signaling tower lights, driving solid-state relays for heaters, and interlocking with external PLCs. Because relay outputs are isolated and can switch AC or DC voltages, the KV-RC8BXR is often used in mixed-voltage panels where a single output module serves both 24V DC signals and 230V AC loads.

Installation and Wiring Guidelines

Mount the unit on a grounded DIN rail. The outputs are grouped into two commons: COM1 (outputs 0-3) and COM2 (outputs 4-7). Each common can be connected to a different voltage source (e.g., COM1 to 24V DC, COM2 to 110V AC). The load is connected between the output terminal and the common. For inductive loads (relays, solenoids), an external suppression diode (for DC) or varistor (for AC) should be placed across the load to prevent contact welding. Do not exceed 2A per common.

Environmental and Compliance

Operating temperature: 0-55°C; storage -20-75°C; humidity 10-95% non-condensing. The unit is rated IP20. It complies with CE, UL 508, and RoHS. Vibration resistance: 5g at 10-55 Hz.

Programming and Addressing

In Keyence KV Studio, the outputs are assigned to a range of internal relays (R) or output bits (R0.0 to R0.7 for the first expansion unit, etc.). The user does not need to set DIP switches; the CPU automatically assigns addresses based on the physical order from the CPU outward. A "Configuration" window in the software shows the I/O mapping.

Maintenance and Fault Detection

If an output LED lights but the load does not operate, suspect a wiring issue or a failed relay. The relays are not field-replaceable; the entire module must be replaced if a contact welds or the coil fails. The unit's front LEDs also flash a diagnostic code (e.g., 2 flashes = bus communication error) if the CPU cannot communicate.

Conclusion

The Keyence KV-RC8BXR expansion output unit provides a convenient, compact means of adding 8 rugged relay outputs to a KV series PLC, suitable for a wide range of industrial switching tasks.