Siemens NXD63B120 Molded Case Circuit Breaker

Both are ND frame breakers with identical mounting footprints and interrupting ratings. The difference lies in the trip unit. The NXD6 features a factory-sealed, non-interchangeable trip unit, while the ND6 allows the trip unit to be swapped in the field.

The thermal protection, or long-time function, is fixed at 1200 amps. However, the magnetic, or instantaneous, trip setting is adjustable. This allows panel builders to fine-tune short-circuit coordination based on specific system requirements.

The NXD63B120 bolt-on breaker is designed for heavy commercial and industrial distribution. It is directly compatible with Siemens P4 and P5 panelboards, as well as standard Siemens switchboards and motor control centers.

ND frame breakers in this size are generally shipped from the factory without lugs installed. You will need to source compatible mechanical lug kits, such as the 3TA4P8500 or 3TA3N8750, depending on your required wire size and conductor material.

No. Because the NXD6 series utilizes a non-interchangeable trip unit, you cannot replace or upgrade the internal module. If a different amperage rating or trip curve is required, the entire circuit breaker must be replaced.

Yes. In addition to its standard AC ratings, this breaker is rated for 500VDC applications with an interrupting capacity of 25kA. When deploying molded case breakers in high-voltage DC applications, always follow Siemens guidelines regarding pole wiring and series connections to properly break the DC arc.

Yes. The Siemens ND frame supports standard internal accessories like shunt trips and auxiliary switches. These components mount inside the breaker housing and must be sourced separately.

Always verify the load is completely de-energized and locked out before removing the breaker cover or adjusting the dials. Adjustments must be performed by a qualified electrician using a coordination study to ensure arc flash and short-circuit safety compliance.