3 Ph AC motor control - correct?

Discussion in 'General Electronics Chat' started by milosz125, Apr 8, 2013.

  1. milosz125

    Thread Starter New Member

    Apr 6, 2012
    2
    0
    Hi All,

    The issue of control systems. I have a dispute with the manufacturer of the control system for a simple three-phase motor.

    The circuit is shown in the attached diagram.

    The control circuit is supplied from 230V AC TN-CS.

    Connection (terminal number according to attached diagram):

    410 - L (phase)

    431 - close (L phase of the "close" button in the main cabinet - remote control)

    433 - open (L phase of the "open" button in the main cabinet - remote control)

    418 - N (Neutral)

    434 - N2 (Neutral from the "close" or "open" button in the main closet - remote control.

    In my opinion, the system is incorrect because it is prone to ground fault.

    For example, when the wire coming out of the terminal A2 of K1E, became loose and touch the metal case (connected to PE), limit switches S1E and S3 are bridged. The fuse of the L side will not switch off in this situation.

    Self start does not occur, but when the motor is running in the "closing" mode iand when final closed position is reached the limit switch S1E does not switch off and in the result mechanical system damage can occur.

    In my opinion the design rule for control systems, where one pole is grounded, is that not to mount the limit switches, contacts,etc between the contactor coil and the grounded pole (in this case, the neutral N).
    For me all the contacts and connectors should be between L and terminal A1 of the contactor.
    Terminal A2 should be directly connected to the N.

    However the manufacturer says that everything is OK.
    What do you think?

    Regards
     
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