The Terasaki XS400ns XS Series air circuit breaker is a fundamental and widely deployed component in marine power systems. Its specification indicates a specific set of features that make it suitable for particular applications onboard vessels.
Here is a detailed overview focused on its role in marine power systems.
Model Designation Breakdown: XS400ns
XS400: 400 Ampere frame size.
n: Fixed version (non-withdrawable).
s: Equipped with the standard S-Type Electronic Trip Relay.
In summary, the XS400ns is a 400A, fixed-mount, intelligent air circuit breaker with a standard breaking capacity.
Key Features & Marine Significance
Fixed Design ('n' Version):
What it means: The breaker is permanently bolted directly to the switchboard's busbars. It does not have a slide-out or draw-out mechanism.
Marine Significance:
Cost and Space Efficiency: Fixed breakers are more compact and less expensive than their withdrawable counterparts. This is ideal for protecting multiple feeder circuits where individual isolation for maintenance is less frequently required.
Simplicity and Reliability: Fewer moving parts can mean higher inherent mechanical reliability.
Disadvantage: To perform maintenance, testing, or replacement, the entire section of the switchboard (or the entire board) must be de-energized. This can lead to more significant downtime compared to a withdrawable unit.
S-Type Electronic Trip Unit ('s' Version):
This is the critical intelligent feature. The S-Type ETR provides fully adjustable protection, which is non-negotiable for a coordinated marine electrical system.
Marine-Specific Protection Settings:
Long-Time Delay (L): Protects cables from overload.
Short-Time Delay (S): Ensures selectivity (discrimination). A fault on a final sub-circuit will trip that local breaker without causing the XS400ns feeder breaker to trip, preventing a blackout for all loads supplied by that feeder.
Instantaneous (I): Provides backup protection for extreme, close-in faults.
Ground-Fault (G): Essential for marine safety. Protects against insulation failure and earth leakage, reducing the risk of fire and electric shock in the humid, conductive shipboard environment. Compliance with marine classification society rules for earth fault protection is mandatory.
Standard Breaking Capacity:
The "ns" model has a robust standard breaking capacity (e.g., 50kA-65kA at 440V). For a 400A feeder breaker located downstream from the main generator breakers, this capacity is often perfectly adequate, as the available fault current diminishes throughout the distribution system.
Marine Environment Durability:
Like all Terasaki XS breakers, the XS400ns is built with corrosion-resistant materials and coatings to withstand salt, moisture, and vibration, which are endemic to the marine environment.
Typical Applications in Marine Power Systems
The fixed nature of the XS400ns makes it ideal for feeder and distribution protection rather than a main incomer role. Common applications include:
Large Feeder Circuits: Supplying power to a dedicated area of the vessel, such as:
Accommodation switchboard
Galley power panel
Workshop machinery panel
Reefer container connection panels
Motor Control Center (MCC) Main Supply: As the incoming breaker for a section feeding multiple motors.
Auxiliary System Feeders: Protecting circuits for large ventilation fans, hydraulic power units, or air conditioning plants.