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Thermal Magnetic MCCB 16A-1600A | 25kA-85kA | Adjustable Trip | IEC 60947-2
Dual Protection for Reliable power
KRIPAL manufactures thermal magnetic molded case circuit breakers (MCCBs) in the UKM1 series for low-voltage power distribution protection from 16A to 1600A with breaking capacities from 25kA to 100kA at 400/690V AC per IEC/EN 60947-2. The UKM1 features a thermal-magnetic trip unit with a bimetallic strip for adjustable overload protection (0.7-1.0 In) and a magnetic coil for fixed or adjustable instantaneous short-circuit protection (5-10 In), providing reliable circuit protection without the need for an external power supply. Available in 3P and 4P configurations in compact frame sizes from 100AF to 1600AF, these MCCBs serve as incoming devices, feeder protection and motor circuit protection in main switchboards, sub-distribution boards and motor control centers. The UKM1 accepts a full range of plug-in accessories including shunt trip, undervoltage release, auxiliary and alarm contacts, motor operator for remote switching, and rotary handle mechanisms with door interlock and padlock facility. Certified to IEC 60947-2 with CE and UKCA marking, KRIPAL MCCBs are shipped to panel builders, switchboard manufacturers and electrical contractors for projects worldwide.
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Ask a QuoteSelecting the Right Thermal Magnetic MCCB for Power Distribution Networks
A molded case circuit breaker provides overcurrent and short-circuit protection for low-voltage power distribution circuits where the fault current exceeds the breaking capacity of miniature circuit breakers. An MCCB uses a rigid molded case housing that contains the arc chamber, and its larger physical size compared to an MCB allows for higher current ratings, higher breaking capacities and adjustable trip settings. The thermal-magnetic trip unit provides two protection functions in one mechanical assembly: a bimetallic strip for thermal overload protection with an inverse time-current characteristic, and a magnetic coil for instantaneous short-circuit protection without intentional time delay. This selection guide covers frame size, current rating, breaking capacity and trip unit adjustment to match your circuit protection requirements.
UKM1 Thermal Magnetic MCCB Series Technical Specifications
Frame Size and Current Range Selection
The UKM1 is available in seven frame sizes: 100AF (16-100A), 160AF (100-160A), 250AF (125-250A), 400AF (200-400A), 630AF (400-630A), 800AF (500-800A) and 1600AF (630-1600A). The frame size (AF, Ampere Frame) defines the maximum current rating that the MCCB’s physical structure can accommodate, while the actual trip unit rating (In) can be adjusted within the frame’s range. For example, a 250AF frame can be equipped with a 200A trip unit and then field-adjusted between 140A and 200A. Selecting the correct frame size involves balancing the installation’s present maximum demand, expected load growth over the equipment’s 20-year service life, and the physical space available in the switchboard. It is generally recommended to select a frame that allows for at least 20 percent spare capacity without moving to the next larger physical size.
Breaking Capacity and System Voltage Matching
The UKM1 breaking capacity (Icu) ranges from 25kA at 400V AC (standard performance, suitable for installations where the switchboard is located more than 50 meters from the supply transformer) to 100kA at 400V AC (high performance, for installations where the switchboard is adjacent to a large transformer and the prospective fault current can exceed 50kA). The required breaking capacity is determined by calculating the prospective short-circuit current at the MCCB’s point of installation using the supply transformer kVA rating, impedance voltage and the cable impedance from the transformer to the switchboard. The UKM1 also offers a service breaking capacity (Ics) that is typically 50-100 percent of Icu, meaning the MCCB can clear a fault at its full rated Icu, be reset, and continue to provide protection without needing replacement.
Thermal-Magnetic Trip Unit Adjustment
The UKM1 thermal trip (overload protection) is adjustable from 0.7 to 1.0 times the trip unit rating (In) via a rotary dial on the front face, allowing the MCCB’s thermal characteristic to be matched to the actual circuit cable ampacity after installation. For example, a 400A trip unit installed on a circuit with 300 sq mm copper cable (ampacity 340A in air at 40 degrees Celsius) would be adjusted to 0.85 In = 340A. The magnetic trip (short-circuit protection) is available as a fixed setting (typically 10 In for standard distribution applications) or adjustable from 5 to 10 In for applications requiring coordination with downstream devices. The adjustable magnetic trip allows the instantaneous pickup to be raised above the downstream MCCB’s let-through threshold, achieving selective coordination where a downstream fault clears locally without tripping the upstream UKM1.
Accessories and Remote Operation
The UKM1 supports a comprehensive range of plug-in accessories that install without tools. A motor operator module allows remote opening and closing via 24V DC or 230V AC control signals from a PLC or SCADA system, enabling automated load transfer and remote circuit restoration. The shunt trip release enables remote tripping from a fire alarm panel or emergency stop circuit. The undervoltage release trips the MCCB when the supply voltage drops, preventing automatic restart of motors. Auxiliary contacts (up to 2 changeover) signal the MCCB open/closed status, and an alarm contact signals when the MCCB has tripped on a fault. The rotary handle mechanism provides a clear ON-OFF-TRIP position indication, with the handle padlockable in the OFF position and a door interlock that prevents the switchboard door from being opened while the MCCB is ON.
Specify MCCBs for Your Switchboard
- Selectivity Study: Submit your single-line diagram and we return a complete protection coordination table with UKM1 settings optimized for discrimination.
- 3D CAD Models: Request STEP files of UKM1 MCCBs for your switchboard layout design, including all accessory configurations.
- OEM Volume Supply: Dedicated production scheduling and JIT delivery for switchboard manufacturers with repeat UKM1 orders.
Power Distribution Protection Across Commercial and Industrial Sectors
KRIPAL UKM1 thermal magnetic MCCBs protect low-voltage power circuits at the main switchboard, sub-distribution board and large equipment feeder level in commercial buildings, industrial plants and infrastructure installations. From the 1600A incoming device on a factory main switchboard to the 100A feeder MCCB on a building floor distribution board, the UKM1 provides adjustable overcurrent and short-circuit protection with selective coordination across multiple levels of the power distribution hierarchy.
Commercial Building Main Switchboard Incoming Device
A 20-story commercial office building’s main LV switchboard uses a UKM1 1600A 4P MCCB with a 65kA breaking capacity as the incoming device from the 2000 kVA supply transformer. The thermal trip is set to 0.9 In (1440A) to protect the 4x 240 sq mm per phase incoming cables, and the magnetic trip is set to 8 In (12,800A) to provide selectivity with the 400A feeder MCCBs on the outgoing circuits. The motor operator allows the facilities manager to remotely open or close the main incoming device from the BMS workstation, enabling automated load shedding during peak demand periods or transfer to the standby generator during a supply outage. The auxiliary contacts signal the MCCB status to the BMS for real-time monitoring of the building’s electrical supply.
Industrial Plant Sub-Distribution Board Feeder
A manufacturing plant’s sub-distribution board serving a production line is fed by a UKM1 400A 3P MCCB from the main switchboard, with a 36kA breaking capacity (adequate for the reduced fault current at the sub-board due to cable impedance). The thermal trip is set to 0.85 In (340A) to protect the 150 sq mm feeder cable, and the magnetic trip is adjusted to 7 In (2800A) to coordinate with the downstream 63A MCBs serving individual machine circuits. The undervoltage release trips the MCCB if the supply voltage drops below 70 percent, preventing the production line motors from automatically restarting when power returns, which would create a safety hazard for maintenance personnel who may be working on the machinery.
Motor Control Center Main Incoming Protection
A motor control center (MCC) serving 20 motor starters in a water treatment plant uses a UKM1 630A 3P MCCB as the main incoming device. The thermal trip is set to 0.9 In (567A), allowing for the combined running current of all motors plus a 20 percent spare capacity. The magnetic trip is adjusted to 10 In (6300A) to prevent nuisance tripping during the simultaneous starting of the two largest motors (which could draw a combined starting current of 4000A for 3-5 seconds). The shunt trip release is wired to the plant’s emergency stop system, allowing a single emergency stop button at the MCC room entrance to trip the main incoming device and de-energize all motor circuits simultaneously.
Data Center UPS Input Protection
A data center’s UPS input circuit is fed by a UKM1 250A 3P MCCB with a 50kA breaking capacity from the main switchboard. The thermal trip is set to 1.0 In (250A) because the UPS input current is essentially constant (the UPS draws constant power from the supply regardless of the load power factor). The magnetic trip is set to 5 In (1250A), the lowest available setting, to provide fast short-circuit protection for the UPS input cable without interfering with the UPS’s internal bypass contactor operation. The motor operator allows the data center BMS to remotely transfer the UPS input from the utility supply to the standby generator during a prolonged outage, with the transfer sequence managed automatically by the BMS.
Crane and Hoist Feeder Protection
Overhead cranes and hoists in factories and warehouses are fed by UKM1 160A 3P MCCBs with the thermal trip set to 0.8 In (128A) to protect the flexible trailing cable that supplies the crane bridge. The magnetic trip is adjusted to 10 In (1600A) to allow for the crane hoist motor starting current (typically 6-8 times full load current) plus the bridge and trolley traverse motors running simultaneously. The shunt trip release is wired to the crane’s upper limit switch, providing a redundant means of disconnecting the crane supply if the hoist overruns the upper limit. The rotary handle on the MCCB is padlocked in the OFF position during crane maintenance, providing a visible isolation point for the crane maintenance team.
Specify MCCB Protection for Your Power Distribution
- Protection Coordination: Our engineers design a complete selectivity scheme for your power distribution system with UKM1 MCCBs at every level.
- Type-Test Certificates: Obtain IEC 60947-2 test reports and discrimination tables for your switchboard IEC 61439 certification.
- OEM Switchboard Supply: Source UKM1 MCCBs pre-assembled on mounting plates with busbar connections for your switchboard production line.
Manufacturing Quality and OEM Supply Capability
KRIPAL thermal magnetic MCCBs are manufactured on a dedicated production line where the molded case is injection-molded from glass-fiber reinforced polyester, the contact assemblies are fabricated from silver-tungsten and silver-graphite composites, and the thermal-magnetic trip units are individually calibrated. Each MCCB undergoes a production-line thermal test and instantaneous trip verification for global power distribution and motor protection applications.
DMC/BMC Molded Case Injection Molding
MCCB cases are injection-molded from glass-fiber reinforced unsaturated polyester (DMC/BMC) using compression molding presses. The material formulation provides CTI above 600V and a UL94 V-0 flammability rating. Molded cases are dimensionally inspected on CMM equipment to verify internal clearances for arc chamber, contact mechanism, and trip unit fit within 0.1 mm tolerance.
Silver-Tungsten and Silver-Graphite Contact Assembly
Main contacts use silver-tungsten (AgW) for high arc erosion resistance and arcing contacts use silver-graphite (AgC) for anti-welding properties. Contact tips are resistance-brazed to copper carriers in a controlled atmosphere furnace. Each contact assembly is measured for contact force and contact gap before installation into the MCCB mechanism.
Thermal-Magnetic Trip Unit Individual Calibration
Each trip unit is individually calibrated on an automated test station. The thermal element (bimetal strip with adjustable heater) is calibrated at 1.05 times and 1.30 times rated current per IEC 60947-2. The magnetic element is set for the instantaneous trip threshold (5 to 10 times rated current for standard distribution, 10 to 14 times for motor protection). Calibration data is recorded per serial number.
Production-Line Temperature Rise and Trip Testing
Every MCCB undergoes a temperature rise test at rated current in free air, with measurements at accessible terminals and on the molded case surface per IEC 60947-2 limits. The instantaneous trip function is verified at 120 percent of the set threshold. Test results are stored against the serial number for full production lot traceability.
Distributor Stock Holding Programs for MCCBs
KRIPAL supports distributor inventory programs with agreed stock levels for standard MCCB models from 16A to 1600A with breaking capacities from 25kA to 85kA. Shipments are planned based on demand data, with scheduled replenishment to maintain stable supply.
Private Label and OEM Branding for MCCBs
Laser-marked part numbers aligned with your catalog, OEM-branded packaging, and customized multilingual instruction sheets are available. Unbranded supply is provided upon request for private label production of MCCBs.
Multi-Region Certification and Compliance Support
CE, UKCA, and IEC 60947-2 EN 60947-2 compliance documentation is provided according to target export markets. Technical documentation files are maintained and updated in line with evolving regulatory requirements for power distribution protection.
Direct Technical Access to KRIPAL Production Engineers
Your technical team communicates with the engineers who designed and calibrated your MCCBs, not a distributor’s sales engineer reading from a catalog. Application questions including selectivity and cascading coordination receive answers within 24 hours during China business hours.
Frequently Asked Questions
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