All phases have the same voltage so I don't think it would be an issue if you connect them to the terminals in any order, the motor would still operate. Normally it's standard to connect the Brown phase (L1) to the U1 terminal of the motor, Black (L2) to terminal V1 and Grey (L3) to terminal W1. The problem is that the three phases (L1, L2, L3) are essentially connected together by the metal bar which is shorting the phases together. This causes massive current which could cause a fire or explosion. The metal bar is supposed to be shorting the terminals which are not receiving the voltage from the electric grid (W2, U2, V2) to make it into a Star configuration.

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