AC Moulded Case Circuit Breaker

Key Selection Factors for Electrical Procurement

Rated Current (In) & Frame Sizes: Choose frame capacities from 63A to 1600A to match main incoming feeders or sub-distribution requirements while optimizing enclosure space.

Breaking Capacity (Icu / Ics) & kA Ratings: Ensure system safety with ultimate breaking capacities (Icu) up to 100kA at 400V/415V. NUOMAK MCCBs offer high service breaking capacity ratios (Ics=100%Icu  on select models), ensuring the breaker remains fully functional after clearing fault currents.

Pole Configurations: Available in standard 3-Pole (3P) for 3-phase industrial power systems and 4-Pole (4P) configurations where neutral isolation or ground fault monitoring is required.

Advanced Trip Unit Protection: Thermal-Magnetic vs. Electronic LSIG

To satisfy diverse client project specifications, NUOMAK provides two primary trip technology lines:

Thermal-Magnetic Trip Units: Proven, economical choice offering reliable inverse-time thermal overload protection (Ir) and instantaneous short-circuit protection (Ii).

Electronic / Microprocessor LSIG Protection: Precision trip units designed for selective coordination and complex protection. Allows independent field adjustments for:

Io/Ir (Long-time delay / Overload setting): Fine-tune continuous current thresholds.

Isd (Short-time delay): Adjustable short-circuit pickup for selective upstream/downstream coordination.

Ii (Instantaneous pickup): Immediate trip response during severe fault currents.

Ig / Ground Fault Protection: Protects against insulation failure and arcing ground faults.

Modular Accessories & OEM Customization

Enhance remote control and automated protection with factory-installed or field-installable accessories, including:

Shunt Trip Coils (Shunt Release): Enables remote tripping upon signal input from emergency stop systems or fire alarms.

Undervoltage Releases (UVR / UV Trip Coils): Automatically trips the breaker during mains voltage drops or power outages to prevent machinery damage.

Auxiliary & Alarm Contacts: Provides real-time status signals (ON/OFF/TRIP) to PLC controllers or supervisory systems.

International Compliance & Quality Assurance

Manufactured under an ISO9001 quality management system, every NUOMAK AC Moulded Case Circuit Breaker undergoes 100% factory routine testing—including dielectric voltage withstand, thermal calibration, and mechanical trip testing—and carries full IEC/EN 60947-2 and CE certifications for seamless import clearance worldwide.

Problem 1: MCCB Trips During Motor Startup (Startup Failure)

Possible Causes:

• High Inrush Current: If the motor uses a direct-on-line (DOL) startup, the starting current can be 8 to 10 times the normal operating current. If the MCCB’s rated current or instantaneous protection multiplier is set incorrectly, it will trip during startup.

• Severe Voltage Drop: If the distribution cabinet is too far from the equipment, the line voltage drop increases. When the terminal voltage falls below the motor’s rated voltage, the startup current will surge, causing a trip.

• Mechanical Overload or Jamming: If the motor starts with a heavy load (e.g., water pumps, conveyor belts) or experiences mechanical jamming/abnormal noise, the starting time becomes too long, and the current spikes, leading to a trip.

Troubleshooting Solutions:

1. Verify if the load uses a direct startup method and measure the actual startup current.

2. Properly calculate and select the MCCB’s rated current and instantaneous protection tripping multiplier.

3. Measure the motor’s terminal voltage (P=IUcos⁡ΦP=IUcosΦ) to ensure it is within the normal range.

4. Inspect the mechanical components of the motor and load to ensure smooth operation without jamming.

Problem 2: MCCB Trips Occasionally During Normal Operation

Possible Causes:

• Three-Phase Unbalance: An unbalanced three-phase load can cause localized overcurrent, leading to tripping.

• Undersized Cables/Busbars: Using connecting cables or copper busbars with an insufficient cross-sectional area will generate excessive heat, causing the MCCB’s thermal protection to trip.

• Loose Connections: If the terminal connection screws are not tightened or have poor contact, the contact resistance will increase significantly. This generates massive heat (sometimes even melting components), triggering the breaker.

• Poor Plug-in Contact: For plug-in or draw-out type MCCBs, loose contacts during installation will cause severe overheating and subsequent tripping.

Troubleshooting Solutions:

1. Check the three-phase current to ensure it is balanced.

2. Verify the cross-sectional area and length of the connecting cables or copper busbars. Replace them with correctly sized ones according to electrical standards.

3. Ensure the MCCB is securely connected to the cables/busbars and thoroughly tighten all connecting screws.

4. For plug-in models, inspect the contact condition and ensure a firm, reliable connection.

Problem 3: Cascading Tripping During a Short Circuit (Lack of Selectivity)

Cascading tripping means a short circuit causes not only the downstream breaker to trip, but also the upstream (higher-level) breaker, causing a wider power outage.

Possible Causes:

• Mismatched Protection Characteristics: This generally occurs because the tripping curves of the series-connected circuit breakers are not properly coordinated. Factors to consider include cable length, cross-sectional area, and the short-circuit clearing time.

Troubleshooting Solutions:

1. Inspect the condition of the breakers on-site. If there is no failure to trip (refusal to operate) on the downstream breaker, the product is functioning normally.

2. Test the tripping characteristics of the breakers to determine if they meet the required specifications.

3. Properly select and coordinate the upstream and downstream MCCBs to ensure selective protection (e.g., matching a low-voltage MCCB with an appropriate upstream MCCB).

What trip unit options (Ir,Isd, LSIG) does NUOMAK offer for AC MCCBs?

NUOMAK provides both standard Thermal-Magnetic trip units and advanced Electronic trip units featuring full LSIG protection (Long-time, Short-time, Instantaneous, and Ground fault). Electronic models allow precise current adjustments (Io,Ir,Isd) directly on the front dial, enabling easy selectivity and precise protection coordination across upstream and downstream circuit breakers.

Can NUOMAK supply factory-fitted accessories like Shunt Trip Coils and Undervoltage Releases?

Yes. We supply a full range of internal and external accessories for our AC MCCBs, including Shunt Trip Coils (AC/DC voltage options), Undervoltage Release Coils (UVR), Auxiliary Contacts, Alarm Contacts, and Extended Rotary Handles. These accessories can be pre-installed at our factory or provided separately for field retrofitting.

What is NUOMAK's wholesale MOQ, lead time, and OEM customization capability?

Our wholesale MOQ for AC MCCBs is 1,000 pieces. Sample lead time is 1–3 days, while bulk orders typically require 30–60 working days, depending on order quantity. We support custom logo branding for OEM orders. Please contact our team to confirm customization requirements and the delivery schedule.