Merlin Gerin NS250H Compact Circuit Breaker | 3 Pole 150A 70kA

Merlin Gerin NS250H Compact Circuit Breaker – 3 Pole, 150 Amps, 70kA

The Merlin Gerin NS250H is an industrial-grade Moulded Case Circuit Breaker (MCCB) from Schneider Electric’s ComPacT Range, designed to deliver reliable motor and electrical distribution protection. This is a 3 poles, 150 Amp breaker, capable of withstanding the most severe thermal and mechanical pressures. It has an outstanding breaking capacity of 70kA @ 380/415V AC. This makes it a good alternative for high fault current applications such as marine vessels, offshore platforms and large manufacturing operations.

The Compact NS250H frame is known for its high power density, dependability and small footprint in marine and heavy industrial engineering circles. It has superior thermal-magnetic or electronic trip devices for reliable protection against overloads and short circuits. This 150A arrangement ensures equal power share in the sub-distribution networks that protect critical downstream equipment from transient faults and catastrophic electrical breakdowns.

Technical Specifications: Compact NS250H

Part Number Cross-References

• Old Merlin Gerin Series: NS250H, NS250 H, NS250-H 150A 3P
• Legacy Schneider Parts: 31670, 31790, 31104
• Modern Replacement Series: ComPacT NSX250H, C25H3TM150, C25H32D250

Where to Use?

1. Marine & Offshore Installations Main switchboard distribution Emergency generator protection Auxiliary machinery panels on Commercial boats Tankers and Drill rigs.
2. Motor Control Centres (MCC): Short-circuit and thermal protection for heavy-duty marine pumps, air compressors, thrusters and ventilation blowers.
3. Industrial Facilities: Protects low-voltage distribution systems in chemical plants, mines and steel mills.
4. Commercial Building Infrastructure: A dependable incoming or feeder breaker for mission essential electrical infrastructure and data centres.

System Compatibility

The NS250H frame fits perfectly into standard Schneider/Merlin Gerin switchboard architectures. It supports direct busbar connections or cable lug terminals with a standard 35 mm connection pitch. It can be paired with common auxiliary accessories, including:

• Under-voltage trips (MN) and Shunt trips (MX)
• Auxiliary contacts (OF) and Fault indicator switches (SD)
• Rotary handles (direct or extended) and plug-in base conversion kits

Shipping and Lead Time Information

• Worldwide Express Shipping: Available via DHL Express, FedEx, and air freight.
• Dispatch Lead Time: Same-day dispatch for emergency breakdowns on in-stock New and Surplus units.

Expert Insights for Senior Chief Engineers & ETOs

1. Handling High Ambient Temperature Derating: In tropical waters or deep inside an engine room casualty zone, ambient temperatures within switchboard cubicles can quickly spike past 50°C. While standard industrial breakers derate heavily at these levels, the high-quality copper and molding compounds used in the Merlin Gerin NS250H allow it to hold its thermal calibration exceptionally well. If utilizing a thermal-magnetic trip unit (TM-D), ensure your ETO references the ambient temperature derating table. At 60°C, a standard 150A thermal strip may trip early near 135A; if you require an absolute uncompromised 150A threshold in hot zones, we highly recommend selecting the STR electronic trip unit configuration which actively calculates internal temperature components accurately.
2. The Criticality of Mechanical Exercising: A common point of failure for MCCBs deployed at sea is “contact welding” or mechanical binding due to salty, humid air settling over months of inactivity. Do not leave this breaker completely untouched. During scheduled bi-annual black-out drills or maintenance windows, manually trip the breaker via its mechanical push-to-trip button at least three times. This clears microscopic oxide films on the internal mechanism pivots and preserves spring tension.
3. Insulation Resistance (Megger) Testing Warning: Before dropping this breaker back into a live marine bus, always run a 500V DC insulation test. However, never Megger test across the poles while an electronic trip unit (STR or MicroLogic) is attached and the breaker is closed, as you risk frying the sensitive internal sensing current transformers and microprocessor logic boards. Test phase-to-phase and phase-to-earth only with the breaker securely open, or temporarily isolate electronic modules if running line tests.