The higher sized switchgear is directly prohibited and exact direction is provided in International Electric Code. And also other country based electric codes around the world covers this specifically. Many expert engineers in the field of operation and maintenance don’t know about this fact. But the design engineers mostly know and practice this code.
The switchgear means circuit breaker like MCB, MCCB. And higher sized is on the basis of cable or wire used. So this concept is for the safety and protection of cable or wire. We can clarify the concept with an example and a direct image that I have compose in MS Powerpoint.
Say in our case if an engineer use 2.5rm sized cable not noticing that a 2.5rm cable can conduct maximum 10amp. Everything will be fine working as the load drawing is 7 to 8 amp, but what about the sole purpose of the circuit breaker- to protect from overload? Say somehow a overload fault happens of 20amp – good enough to damage the load and the wire or the load is fine with it. The circuit breaker will do nothing, as it is set to detect 0 to 39 amp as permissible current. Than can you imagine what would happen the 2.5rm cable.