Merlin Gerin C1251 NDC Circuit Breaker

Merlin Gerin C1251 NDC Compact Circuit Breaker | 3 Pole, 1250 Amp, 750V

The Merlin Gerin C1251 NDC is a heavy-duty, 3-pole Molded Case Circuit Breaker (MCCB) engineered for main low-voltage power distribution networks, commercial installations, and demanding marine environments. Operating with a nominal continuous current rating of 1250 A and an insulation voltage rating of 750 V AC, this breaker provides critical selective protection against extended thermal overloads and high-energy short-circuit faults.

Equipped with electronic trip logic (commonly the STR25DE trip system), the C1251 NDC delivers precise adjustability for long-time and instantaneous or short-time thresholds. Its compact frame allows direct integration into space-constrained motor control centers (MCCs), generator synchronizing panels, and marine main switchboards (MSB).

Model Details

• Manufacturer: Merlin Gerin (Now Schneider Electric)
• Range: Compact C Series
• Model Code: C1251 NDC
• Manufacturer Part Number (MPN): C1251NDC / C1251-NDC
• Trip Unit Compatibility: STR25DE / STR35SE / STR55UE solid-state electronic trip releases
• Number of Poles: 3 Poles (3P, 3-Phase)

Technical Specifications

Key Features

1. Robust 50 kA Fault Interruption: Utilizes rapid-arc extinguishing chambers with de-ion plates capable of clearing destructive faults up to 50 kA without terminal erosion.
2. Configurable Electronic Protection: Solid-state STR electronic module allows fine calibration of continuous current pickup and short-circuit delays for absolute discrimination.
3. Integrated True RMS Sensing: Electronic trip unit prevents nuisance tripping caused by non-linear loads, harmonic distortion, variable frequency drive (VFD) outputs, or thyristor systems.
4. Heavy-Duty Busbar Integration: Direct-mount terminal allocations accept copper busbar drops or multi-cable lug adapters rated to handle full 1250A thermal continuous loading.
5. Category B Discrimination: Engineered with a 15 kA 1-second short-time withstand enabling full downstream coordination without tripping main incoming feeds.

Applications

• Marine vessel Main Switchboards (MSB), Emergency Switchboards (ESB), and auxiliary generator feeder systems.
• Heavy marine consumers, including bow thruster distribution panels, deck winches, and propulsion drive isolation.
• Commercial power distribution switchgear and transformer secondary protection assemblies.
• Industrial motor control centers (MCC) protecting continuous-duty high-horsepower pump and compressor arrays.
• Critical infrastructure standby power and automatic transfer switch (ATS) systems.

Equipment Compatibility & Direct Cross-References

• Direct Mechanical & Electrical Equivalents:
  • Square D C1251N / C1251H (Compact Type C frame)
  • Schneider Electric MasterPact / Compact NS1250N (Modern retrofit / functional successor)
  • Merlin Gerin Compact C801, C1001, and C1251 frame variants
• Panelboard Compatibility:
  • Merlin Gerin Prisma P & G cubicle enclosures
  • Schneider Electric Okken switchboards
  • Marine standard type-tested marine cubicles (ABB, Siemens, Terasaki retrofits with transition bus work)

Frequently Asked Questions

What is the functional difference between the C1251 NDC and the standard C1251 N breaker?

The “NDC” designation typically identifies specialized continuous breaking capacity, specific terminal configurations, or industrial DC/marine application ratings tailored for selective tripping coordination, whereas “N” represents the standard commercial distribution breaking frame.

Can the Merlin Gerin C1251 NDC be retrofitted with a modern Schneider Electric equivalent?

Yes. Modern Schneider Electric Compact NS1250 or MasterPact NW/MTZ frames can replace the legacy C1251. Retrofit kits and copper terminal bus adaptors are available to convert rear-stud configurations without modifying your enclosure doors or switchboard bus runs.

How do I adjust the STR electronic trip unit settings?

The front faceplate features rotary potentiometers for and along with for short-time delay thresholds. Simply rotate the sealed dials using an insulated flat-head screwdriver until the indicator aligns with the calculated protection study figures.