Chassis tuck is mainly used to hold circuit breaker transformer and other components in the withdrawable switchgear,chassis push and exit them. And chassis as an auxliary operation for connecting components and busbars.When operation with internal mechanism of circuit breaker and other interlock mechanism of mid-placed cabinet t can satisfy the interlock requirement of“5 preventions”stpulated in GB3906.Specific functions are as follows: Only when the handcart is under testing/isolating or working position, the circui breaker can be closed.After that, the handcart is underlocked state,which prevents misconnection and mismatched isolation contacts with load.