Whether it is a fixed board such as GGD or a withdrawable one such as MNS, a low-voltage distribution cabinet is built from the same families of parts.
Enclosure
A steel frame carries the weight of the equipment and resists short-circuit forces. Panels and doors keep out dust, moisture and fingers; the degree of protection (for example IP30 or IP40) is chosen for the room.
Busbars
The main busbar takes power from the incoming supply and distributes it along the board; its size follows the rated current and the short-circuit level. Branch busbars carry power from the main bar to each outgoing unit.
Components
- Circuit breakers for switching and protection against overload and short circuit; residual-current devices for earth leakage; automatic transfer switches for dual supplies
- Contactors for frequent switching, typically of motors
- Relays for control, interlocking and protection logic
- Fuses for simple, reliable short-circuit protection
- Current and voltage transformers for metering and protection
- Capacitor banks for power factor correction
- Meters and protection relays that monitor the system and can report remotely
Wiring
Terminal blocks and control wiring connect it all; conductor sizes follow the current, voltage and ambient temperature.