Here is a detailed breakdown of the Terasaki XS100ss and its role in marine power systems.
Overview: Terasaki XS100ss
The model name "XS100ss" decodes as follows:
XS: Series name.
100: The frame size, indicating a rated current of up to 1000 Amps.
ss: This is the most important differentiator. The "ss" typically stands for Standard Breaking Capacity or, more specifically in Terasaki's context, it signifies a focus on a specific protection characteristic. It is often associated with a current-limiting design with a very fast response to short-circuit faults, but with a standard or lower ultimate breaking capacity (Icu) compared to the "hs" model.
Key Characteristics of the XS100ss:
Rated Current (Iu): Up to 1000A.
Breaking Capacity (Icu): Lower than the "hs" version. While still high, it is designed for points in the network where the available fault current is less extreme. It might be in the range of 50kA-65kA at 415V, for example.
Current Limiting Design: This is a core feature. The "ss" breaker is engineered to interrupt a short-circuit fault extremely rapidly (within the first millisecond), which limits the peak let-through current (Ip) and thermal energy (I²t). This protects downstream components like cables, contactors, and motor starters that may have lower withstand ratings.
Tripping Unit: Equipped with a standard Electronic Trip Unit (ETU) providing fully adjustable protection (Long-time, Short-time, Instantaneous, and Ground Fault).
Application in Marine Power Systems
The XS100ss finds its niche where selective coordination and protection of downstream equipment are more critical than withstanding the absolute highest fault currents found at the main busbar.
Its primary roles are:
Sub-Distribution Feeder Protection:
This is the most common role. The XS100ss is an ideal incoming breaker for a Sub-Switchboard or Distribution Board (e.g., an Engine Room Auxiliary Board, Accommodation Board, or Deck Board).
It provides the main protection for that entire section of the ship's electrical network.
Direct Protection of Large Motors:
It can be used as the main breaker for large motor circuits, such as for large pumps (ballast, fire, cargo) or fans. Its current-limiting nature is excellent for protecting the motor and its starting equipment (e.g., soft starters or variable frequency drives) from the destructive energy of a short-circuit.
Providing Cascading Coordination:
The "ss" breaker is perfectly suited for a cascading protection scheme. Its high-speed interruption limits the fault current that downstream, smaller Molded Case Circuit Breakers (MCCBs) are exposed to. This allows the use of MCCBs with a lower breaking capacity, which is a cost-effective and space-saving solution.
Why Choose the XS100ss? The "Current Limiting" Advantage
The key reason to select an "ss" model over an "hs" or "ns" is its focused protection strategy.
An XS100hs is designed to withstand and interrupt a very high fault current. It's a "stronghold" for points close to the main source of power.
An XS100ss is designed to limit the let-through energy of a fault. It's a "protective shield" for downstream equipment.
Scenario: Imagine a short-circuit occurs in a motor control center fed by a sub-switchboard.
The XS100ss will trip so fast that the fault current doesn't have time to reach its full prospective value.
This reduced let-through energy is now within the withstand rating of the motor starter components and cables downstream.
This prevents "blow-ups" in the motor control center, enhancing safety and reducing damage.
Comparison with Other XS100 Models
Feature Terasaki XS100ss Terasaki XS100hs
Suffix Meaning Standard Breaking Capacity / Current Limiting focus High Breaking Capacity
Primary Strength Very fast interruption to protect downstream gear Ability to withstand & interrupt extremely high faults
Typical Icu Lower (e.g., 50-65kA) Very High (e.g., 85-100kA+)
Best Used For Sub-switchboard incoming, motor feeders, cascading schemes Main switchboard feeders, locations with very high available fault current
System Level Tertiary Distribution / Load Protection Primary & Secondary Distribution
Summary
The Terasaki XS100ss is a highly effective current-limiting air circuit breaker designed for marine applications where the protection of downstream equipment and selective coordination are paramount. While it may not have the ultimate breaking capacity of the "hs" model, its speed and current-limiting action make it an intelligent choice for safeguarding sub-distribution networks and expensive motor loads, preventing extensive damage and improving the overall safety and reliability of the vessel's electrical system.