Low-Voltage Switchgear Assembly: Definition & Key Classifications​

Core Definition:
A Low-Voltage Switchgear Assembly comprises one or more low-voltage switching devices, integrated with associated control, measurement, signaling, protection, and regulation equipment. The manufacturer completes all internal electrical and mechanical connections, assembling the components into a structurally complete unit within an enclosure.

Classification by Design Verification Level:

1. Fully Type-Tested Assembly (TTA):

• Conforms to a verified design series.

• Demonstrates full compliance with IEC 61439.1 through comprehensive type testing.

• Exhibits no deviations from the tested prototype that could impact performance.

2. Partially Type-Tested Assembly (PTTA):

• Integrates both type-tested components and non-type-tested elements.

• Non-type-tested sections derive from validated designs (e.g., via calculation-based extensions of tested configurations).

Classification by Construction:

• Fixed Mounting Design: Power Center (PC) or Motor Control Center (MCC) circuits installed without withdrawal capability.

• Withdrawable/Draw-Out Design: PC or MCC circuit breakers designed for safe isolation and removal while the assembly remains energized.

Classification by Primary Function:

• Power Distribution (PCC - Power Control Center): Feeder panels distributing primary power.

• Motor Control (MCC - Motor Control Center): Panels dedicated to starting, stopping, and protecting electric motors.

• Power Factor Correction: Capacitor banks for reactive power compensation.

Key Assembly Components:

1. Enclosure: Structural chassis, supporting framework, and internal mounting hardware.

2. Busbars: Low-impedance conductors distributing power to multiple circuits.

3. Functional Unit: Integrated assembly of electrical and mechanical components performing a specific function (e.g., incoming feeder unit, outgoing circuit unit).

Internal Partitioning (Segregation Types - IEC 61439):

• Type 1: No internal barriers between functional zones.

• Type 2: Segregation between busbars and functional units only.

• Type 3:

• Segregation between busbars and functional units.

• Segregation between adjacent functional units.

• Segregation between functional units and outgoing terminals/cable connections.

• Type 4 (Highest Segregation):

• Segregation between busbars and functional units.

• Segregation between adjacent functional units.

• Segregation between functional units and outgoing terminals/cable connections.

• Segregation between outgoing terminals/cable connections of adjacent units.

• Common Partitioned Compartments: Busbar chamber (horizontal/vertical), Functional unit compartment, Cable termination chamber, Auxiliary (control) compartment.

Critical Technical Parameters:

• Rated Operational Current (Ie): Typically matches the main incoming circuit breaker rating.

• Rated Operational Voltage (Ue) / Rated Insulation Voltage (Ui): e.g., 690V / 1000V.

• Termination Types: Cable entry/exit methods (top/bottom/side, glands, bushings).

• Rated Short-Time Withstand Current (Icw): RMS current the assembly can safely carry for a specified time (typically 1 second).

• Degree of Internal Separation: Defined by Segregation Type (1-4).

• Ingress Protection (IP) Rating: Enclosure protection against solids/liquids.

• Installation: Mounting location (indoor/outdoor) and method (floor-standing, wall-mount).

• Dimensions: External HxWxD dimensions (impacting floor space).

• Finishing: Coating type, color (RAL codes).

• Earthing System: Design and specifications.

• Busbar Parameters:

• Rated Current (determines cross-section/material).

• Rated Short-Time Withstand Current (Icw).

• Rated Peak Withstand Current (Ipk = Typically 2.2 x Icw).

• Surface Treatment: Tin plating, silver plating, nickel plating for reduced resistance/corrosion protection.

Functional Unit Connection Types:

• Fixed: Main circuit connections can only be made/broken when the assembly is isolated/de-energized.

• Removable (Disconnectable): Can be safely disconnected/isolated from the main circuit while the assembly is live. Includes "Connect" and "Disconnect/Remove" positions.

• Withdrawable: Can be safely isolated, tested, disconnected, and fully removed while the assembly is live. Includes "Connect," "Test," "Disconnect/Isolate," and "Remove" positions.

IP Code (Ingress Protection) Breakdown:

• First Digit - Solid Particle Protection:

• 0: No protection

• 1: >50mm objects

• 2: >12.5mm objects

• 3: >2.5mm objects

• 4: >1.0mm objects

• 5: Dust protected (limited ingress)

• 6: Dust tight

• Second Digit - Liquid Ingress Protection:

• 0: No protection

• 1: Vertically falling drops

• 2: Vertically falling drops (tilted up to 15°)

• 3: Spraying water (up to 60° from vertical)

• 4: Splashing water (from any direction)

• 5: Low-pressure water jets (from any direction)

• 6: Powerful water jets / Heavy seas

• 7: Temporary immersion (1m depth for 30 min)

• 8: Continuous immersion (specified depth/time)