Form 1
Form 1 – No Internal Segregation
- All functional units (busbars, terminals, control devices, cables) are in a single compartment.
- No partitions between busbars, feeders, or terminals.
- Cheapest and simplest construction, but least safe.
- Suitable only for very basic applications.
Form 2a
Form 2a
Form 2 – Segregation of Busbars
- Busbars are separated from the functional units (circuit breakers, feeders, etc.).
- Prevents direct contact with busbars during maintenance.
- Two types 2a and 2b:
Form 2a: Busbars and feeder compartments are not fully separated; basic barrier protection only.
Form 2b
Form 2b
Form 2a
Form 2b: Busbars and feeder compartments are physically separated by barriers for improved safety.
Form 3a
Form 2b
Form 3a
Form 3 – Segregation of Functional Units
- Busbars are separated, and each functional unit (e.g., each circuit breaker) is in its own compartment.
- Prevents faults in one unit from spreading to another.
Form 3a: Terminals for external conductors are in the same compartment as the functional unit.
Form 3b
Form 2b
Form 3a
Form 3b: Terminals are in a separate compartment from busbars and other functional units. External cabling terminals are not segregated from busbars.
Form 4a
Form 4a
Form 4a
Form 4 – Full Segregation (Highest Level)
- Busbars, functional units, and terminals for external cables are all separated from each other.
- Allows maintenance of one unit without disturbing others.
- Provides maximum safety and reliability.
Form 4a: Terminals for external conductors are in the same compartment as the functional unit but segregated from busbars.
Form 4b
Form 4a
Form 4a
Form 4b: Terminals for external conductors are in separate compartments from both the busbars and the functional unit.