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Air Circuit Breakers ACB | 630A-6300A | Draw-Out Type | 150kA | IEC 60947-2
High-Capacity Protection from a Professional Factory
KRIPAL manufactures air circuit breakers (ACBs) in the UKA1 series for main power distribution protection in low-voltage switchboards, with rated currents from 630A to 6300A and breaking capacities from 65kA to 100kA at 400/690V AC per IEC 60947-2. The UKA1 features a microprocessor-based electronic trip unit with an LCD display providing real-time current, voltage, power and energy measurements, plus fully adjustable protection functions: long-time delay (L), short-time delay (S), instantaneous (I) and ground-fault (G) with configurable I squared t or definite time curves. The ACB uses a stored-energy spring mechanism that can be manually or motor-charged, providing consistent closing speed independent of the operator. Available in fixed and drawout versions with 3P and 4P configurations, the UKA1 includes integrated Modbus RTU and optional Profibus/DeviceNet communication for integration with power monitoring and SCADA systems. Certified to IEC 60947-2 with type-tested short-circuit ratings verified by independent laboratory testing, KRIPAL ACBs are the standard incoming and bus-coupler device in main LV switchboards for industrial plants, commercial high-rise buildings, data centers and infrastructure projects.
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ACB Selection for Main Switchboard Incomer Protection
An air circuit breaker is the highest-capacity low-voltage protection device, rated for continuous currents up to 6300A and fault currents up to 100kA. The ACB uses atmospheric air as the arc extinguishing medium, with the arc being drawn into a segmented arc chute where it is split, cooled and deionized until extinction. The stored-energy spring mechanism ensures consistent contact closing speed and force regardless of whether the operator is manual (a charging handle) or motorized, eliminating the risk of contact welding due to a slow manual close. The electronic trip unit provides the most comprehensive protection and measurement capabilities of any LV circuit breaker, transforming the ACB from a simple protection device into an intelligent power monitoring node in the facility’s electrical network. This selection guide covers frame size, trip unit functions, communication options and mounting configuration.
UKA1 ACB Series Technical Specifications
Frame Size and Current Rating Selection
The UKA1 is available in four frame sizes: Frame 1 (630-1600A), Frame 2 (1600-2500A), Frame 3 (2500-4000A) and Frame 4 (4000-6300A). The frame size defines the physical dimensions of the ACB, the busbar connection interface, and the maximum current rating. The actual trip unit rating is set electronically and can be adjusted in the field without changing any hardware component. For a 2000 kVA transformer with a secondary full-load current of 2887A at 400V, a Frame 3 3200A ACB with the trip unit set to 0.9 In (2880A) provides operating margin for transformer overload capability (typically 110 percent for 30 minutes per IEC 60076) while protecting the secondary cables. The ACB’s continuous current rating must also account for the switchboard enclosure’s internal ambient temperature, which is typically 10-15 degrees Celsius above the switch room ambient due to the heat generated by busbars and cable connections.
LSIG Protection Functions and Coordination
The UKA1 electronic trip unit provides four independently adjustable protection functions. Long-time (L) protects against sustained overload with an I squared t thermal memory characteristic, adjustable pickup from 0.4-1.0 In and time from 0.5-30 seconds at 6 times the pickup. Short-time (S) provides selective coordination with downstream MCCBs, with adjustable pickup from 1.5-10 times the L pickup and time delay from 0.1-0.4 seconds (with I squared t ON for coordination with thermal devices or OFF for definite-time coordination). Instantaneous (I) clears bolted faults, adjustable from 2-15 times In, with an OFF setting available for applications where instantaneous protection must be disabled to maintain selectivity with downstream devices. Ground-fault (G) detects phase-to-earth faults, with adjustable pickup from 0.2-1.0 times In, time delay from 0.1-0.4 seconds, and I squared t ON/OFF. The G function can use either the residual current calculated from the three phase current sensors or a separate neutral sensor for direct measurement.
Power Metering and Communication Integration
The UKA1 trip unit includes an integrated power quality meter that measures and displays on the LCD: phase currents (Ia, Ib, Ic, In), phase-to-phase and phase-to-neutral voltages, active/reactive/apparent power per phase and total, power factor, frequency, active and reactive energy (import and export, 4-quadrant), and total harmonic distortion (THD) for voltage and current. The measurement accuracy is Class 1 for current and voltage per IEC 61557-12, making the ACB suitable for sub-billing applications without a separate revenue meter. Communication is via Modbus RTU (RS-485, standard on all units) or optional Profibus DP and DeviceNet for integration with PLC-based control systems. The trip unit stores the last 20 trip events with date/time stamp, fault type, and the current/voltage values at the moment of trip, enabling post-fault analysis without additional disturbance recording equipment.
Drawout Configuration and Maintenance
The UKA1 drawout version uses a racking mechanism with three defined positions: CONNECTED (power and control circuits engaged), TEST (control circuits engaged, power circuits isolated, allowing trip unit configuration and testing without energizing the load) and ISOLATED (all circuits disengaged, ACB can be removed from the switchboard). The racking mechanism includes a safety shutter system that covers the fixed power contacts when the ACB is racked out, providing IP2X finger protection for the operator. The ACB can be racked from CONNECTED to ISOLATED and removed in under 5 minutes by a single electrician, compared to 2-3 hours for a fixed ACB that requires disconnecting and reconnecting bolted busbar joints. For critical installations, a spare ACB can be kept in the switch room, tested in the TEST position, and swapped in during a scheduled maintenance window with minimal downtime.
Specify ACBs for Your Main Switchboard
- Protection Coordination Study: Our engineers design a complete LSIG protection scheme for your power distribution network with UKA1 settings.
- Power Monitoring Integration: Request the Modbus register map and configuration guide for integrating UKA1 measurements into your BMS or SCADA.
- OEM Switchboard Supply: Source UKA1 ACBs pre-configured with trip unit settings and factory witness-tested for your switchboard project.
Main Incomer Protection for Critical LV Switchboards
KRIPAL UKA1 air circuit breakers are the primary protection and control devices at the main LV switchboard level in large industrial, commercial and infrastructure installations. From the 4000A incoming ACB on a factory main switchboard to the 2500A bus-coupler ACB in a hospital’s dual-supply switchboard, the UKA1 provides the highest level of protection coordination, power monitoring and remote control capability available in a low-voltage circuit breaker.
Industrial Plant Main Incoming ACB
A manufacturing plant with a 2500 kVA supply transformer uses a UKA1-4000A Frame 3 drawout ACB as the main incoming device. The LSIG protection is coordinated with the transformer’s damage curve (the “S” short-time delay is set below the transformer’s thermal and mechanical withstand limits per IEC 60076-5) and with the downstream MCCB feeder devices. The integrated power meter measures the plant’s total power consumption, power factor and harmonic distortion, data that is transmitted via Modbus to the plant’s energy management system for ISO 50001 energy performance reporting. During the annual plant shutdown, the ACB is racked out to the ISOLATED position, the contacts and arc chute are inspected, and the trip unit is tested by secondary injection from a portable test set, all without disconnecting the fixed busbar connections.
Hospital Dual-Supply Bus-Coupler ACB
A hospital’s essential electrical supply uses two UKA1-2500A ACBs (one on each utility incomer) and a third UKA1-2500A bus-coupler ACB between the two busbar sections. During normal operation, both incomers are closed and the bus-coupler is open. If one utility supply fails, the affected incomer ACB opens, the bus-coupler closes, and the entire hospital load is supplied from the remaining healthy incomer, with the transfer sequence automatically managed by the switchboard’s PLC controller. The bus-coupler ACB’s short-time delay is set to coordinate with both incomers, and its instantaneous protection is set to OFF to prevent a busbar fault from tripping all three ACBs simultaneously, which would cause a complete blackout of the hospital.
Data Center UPS Output Distribution ACB
A data center’s UPS output switchboard uses UKA1-1600A ACBs as the feeder devices to each server room power distribution unit (PDU). The ACB’s power meter measures the PDU’s energy consumption and reports it to the data center infrastructure management (DCIM) system, enabling per-PDU energy billing for colocation customers. The harmonic distortion measurement monitors the server power supply harmonic current injection, alerting the facilities team if the THD exceeds the UPS’s capability, indicating failing power supply capacitors that should be replaced during the next maintenance window. The event log captures any trip events with pre-fault current and voltage waveforms, enabling root cause analysis of server room power outages.
Commercial High-Rise Bus Riser ACB
A 40-story commercial tower uses UKA1-2000A ACBs at the main switchboard to feed the vertical busbar risers that supply each floor’s distribution board. The ACB’s LSIG settings are coordinated with the MCCBs at each floor, and the ground-fault protection is set to detect arcing faults in the busbar riser (a known failure mode in aging busbar systems where insulation degradation leads to phase-to-earth arcing). The ACB’s Modbus communication reports the current on each riser to the BMS, and if one riser current drops to near zero (indicating the floor’s main MCCB has tripped or the busbar connection has failed), the BMS generates an alarm for immediate investigation by the facilities team.
Generator Synchronizing Circuit Breaker
A standby power system with multiple generators operating in parallel uses UKA1-3200A ACBs as the generator circuit breakers. The ACB’s trip unit measures the generator’s output voltage, frequency and phase angle, data that is used by the synchronizing controller to match the generator’s output to the busbar before closing the ACB. The motor operator closes the ACB within 50ms of receiving the close command from the synchronizer, ensuring the generator connects to the busbar at the optimal phase angle for minimal transient current. The ACB’s power meter measures the generator’s kW and kVAr output, enabling the load-sharing controller to adjust each generator’s fuel governor and AVR for equal active and reactive power sharing.
Engineer Your Main Switchboard Protection
- Protection and Coordination: Our power systems engineers design the complete ACB protection scheme with LSIG settings verified for your network.
- FAT Witness Testing: Schedule a factory acceptance test of your UKA1 ACBs with secondary injection verification of all protection functions.
- OEM Partnership: Dedicated ACB production scheduling and JIT delivery for switchboard manufacturers with project-based requirements.
KRIPAL ACB Manufacturing: Engineered for Ultimate Protection
KRIPAL air circuit breakers are manufactured in a dedicated 5000 sqm assembly hall with climate-controlled environment for the electronic trip unit calibration. Each ACB undergoes a complete functional test sequence including contact resistance measurement, trip unit calibration across all protection functions, and mechanical endurance cycling for global main switchboard and power distribution applications up to 6300A.
Climate-Controlled Assembly and Calibration Environment
ACB assembly is performed in an environment maintained at 22 plus or minus 2 degrees Celsius and 50 plus or minus 10 percent relative humidity. This environmental control is essential for the precision calibration of electronic trip units where temperature drift in reference components could affect protection accuracy at the microsecond level.
Electronic Trip Unit Multi-Function Calibration
Each microprocessor-based trip unit is calibrated for the full protection suite: long-time delay (L), short-time delay (S), instantaneous (I), and earth fault (G). Calibration is performed by injecting precision current signals into the trip unit’s sensing inputs and verifying trip times at multiple points on each protection curve against the published time-current characteristics.
Draw-Out Cassette and Main Contact Cluster Assembly
The draw-out mechanism incorporates silver-plated copper contact clusters with multiple independent contact fingers per pole for current sharing. Each cluster is measured for individual finger contact resistance and total cluster resistance. The cassette racking mechanism is tested for insertion/withdrawal force and for correct operation of the position indicator (CONNECTED, TEST, ISOLATED).
End-of-Line Functional Test Sequence
Every ACB undergoes a complete end-of-line test: main contact resistance (four-wire at 100A DC), dielectric withstand at 2500V between open contacts and between poles, trip unit functional test on all protection functions, mechanical endurance (50 close/open cycles with stored-energy mechanism), and undervoltage release and shunt trip verification.
Distributor and Project Stock Programs for ACBs
KRIPAL supports project-specific delivery scheduling for ACBs with agreed lead times. Critical spare parts and interchangeable trip units are maintained in stock for rapid shipment to minimize switchboard downtime during maintenance or retrofit projects.
Private Label and OEM Branding for ACBs
Custom nameplates, OEM trip unit firmware branding (where applicable), and project-specific documentation packages are available. KRIPAL supports the supply of ACBs with customer-specified protection settings pre-configured at the factory for panel builder integration.
Multi-Region Certification and Compliance Support
CE, UKCA, and IEC 60947-2 compliance documentation is provided. Type test certificates from accredited laboratories (ASTA, KEMA, or equivalent) are available for the complete ACB range, supporting switchboard manufacturers’ conformity assessments.
Direct Technical Access to KRIPAL ACB Engineers
Your technical team communicates directly with the ACB design and production engineers. Application questions including selectivity studies, busbar connection details, and arc flash incident energy calculations receive answers within 24 hours during China business hours.
Frequently Asked Questions
Explore FAQ >When rated current exceeds 1600A (MCCB limit), when breaking capacity requirements exceed 85kA, or when draw-out construction is required for maintenance without busbar shutdown.
The breaker can be withdrawn for maintenance while the busbar stays energized. Connected, Test and Isolated positions provide safe, controlled isolation.
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