A chassis truck (Cassette / Cradle) serves as the movable base for vacuum circuit breakers and other components in withdrawable switchgear. Its primary function is to enable the safe, stable, and precise positioning of the breaker, whether in the working position, test/isolation position, or during withdrawal. Typically equipped with a smooth maneuvering system, it allows operators to control movement effortlessly while maintaining alignment with the switchgear busbar.

In addition to circuit breakers, chassis trucks can also accommodate transformers and other switchgear modules, acting as an auxiliary connection between these components and the busbar. When integrated with the circuit breaker’s internal mechanism and the switchgear’s interlock system, the chassis truck can fully comply with the GB3906 “Five-Prevention” safety requirements, which are designed to eliminate hazardous misoperations:

1. Breaker operation interlock – The breaker can be closed only when the handcart is in the working or test/isolation position. Once closed, the handcart is locked to prevent unintended movement.
2. Earthing switch interlock – When the handcart is in the working position or slightly withdrawn (about 10 mm) from the test/isolation position, the earthing switch cannot be engaged, preventing unsafe grounding under load.
3. Movement restriction with earthing switch engaged – If the earthing switch is closed, the handcart cannot be moved into the working position, avoiding accidental breaker closure into a grounded circuit.
4. Withdrawal restriction – Once the handcart leaves the test/isolation position, it cannot be removed from the cabinet, ensuring proper operating sequence.

Motorized (Electric) Chassis Truck

The motorized version is developed from the manual chassis truck, offering electric actuation for automation, remote control, and programmable operation—ideal for modern intelligent switchgear systems. Despite the added functionality, it maintains the same dimensions as the manual model for seamless interchangeability.

Over multiple generations of development—now in its fourth-generation hybrid design—the motorized chassis truck has adopted a micro permanent-magnet DC motor since the third generation, enabling higher precision, reduced maintenance, and full utilization of internal space without altering the unit’s size or core functions.