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Thread: extruder lockout/estop

  1. #1
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    extruder lockout/estop

    I work in a plant doing polymer extrusion.

    Recently an insurance guy was walking through the plant and noticed the way we lock out the machines to clean them.

    there is no real way to get a hand stuck in the extruder screw.

    What are your thoughts as to whether or not this meets minimum requirements?

    Should there be knife switch or contactor means of disconnect?

    this is an exampleClick image for larger version. 

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    Locking out that control switch still leaves some possibility of the motor unexpectedly starting. Should something crush the control circuit cable and short the two main control leads together the drive will see that as a run command.

    Opening the drive supply conductors or even the motor conductors with something that will not close (and then locking it open) is much more reliable at preventing that motor from unexpectedly starting from a safety perspective.
    I live for today, I'm just a day behind.

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    Quote Originally Posted by kwired View Post
    Locking out that control switch still leaves some possibility of the motor unexpectedly starting. Should something crush the control circuit cable and short the two main control leads together the drive will see that as a run command.

    Opening the drive supply conductors or even the motor conductors with something that will not close (and then locking it open) is much more reliable at preventing that motor from unexpectedly starting from a safety perspective.
    Or a single failure in the drive itself, for that matter.
    NEC and OSHA may have slightly different rules on disconnects when intended only for mechanical maintenance. For electrical work that circuit would not count.

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    Quote Originally Posted by GoldDigger View Post
    Or a single failure in the drive itself, for that matter.
    NEC and OSHA may have slightly different rules on disconnects when intended only for mechanical maintenance. For electrical work that circuit would not count.
    OP's question is mostly about clean out of the equipment, so lockout in question is mostly about mechanical lockout. If the breaker/disconnect supplying the drive is capable of being locked that may be just fine for the insurance inspector mentioned in the OP.
    I live for today, I'm just a day behind.

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    A device that does not open the power conductors is never suitable for use as a disconnect or a lockout.
    Don, Illinois
    (All code citations are 2017 unless otherwise noted)

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    contactor

    Here is language from OSHA.

    Energy isolating device. A mechanical device that physically prevents the transmission or release of energy, including but not limited to the following: A manually operated electrical circuit breaker; a disconnect switch; a manually operated switch by which the conductors of a circuit can be disconnected from all ungrounded supply conductors, and, in addition, no pole can be operated independently; a line valve; a block; and any similar device used to block or isolate energy. Push buttons, selector switches and other control circuit type devices are not energy isolating devices.

    -------------------------------------------------------------

    from what i read here. using this type of switch along with a contactor, removing power from the line side of the drive should meet requirements

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    Quote Originally Posted by smoky View Post
    I work in a plant doing polymer extrusion.

    Recently an insurance guy was walking through the plant and noticed the way we lock out the machines to clean them.

    there is no real way to get a hand stuck in the extruder screw.

    What are your thoughts as to whether or not this meets minimum requirements?

    Should there be knife switch or contactor means of disconnect?

    this is an exampleClick image for larger version. 

Name:	estop.jpg 
Views:	116 
Size:	61.2 KB 
ID:	22415
    Click image for larger version. 

Name:	20190225_125322.jpg 
Views:	160 
Size:	129.3 KB 
ID:	22414
    We wouldn't get by with anything less than a padlocked off input isolator and LOTO.
    Lock off, tag off.
    And that's just a British way of doing things. We were owned by one of the major US electrical giants.

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    If I was doing this install, I would put a lockable disconnect at the motor, to open the motor leads, and put aux contacts in the disconnect wired to your stop circuit. That way, when the disconnect is open, the drive can't start. The disconnect satisfies LOTO, and prevents the motor from running, and the aux contacts protect the drive if it tries to start with no load (motor) connected.

    Also, if you are using an Allen Bradley drive that has safe torque off (STO) inputs, use those for your e-stop, not the stop input. Other brands have similiar features. That will provide a safety rated way to stop the drive when the e-stop is pushed. Also, it will disconnect power to the motor right away, versus the stop input that may have a ramp time programmed.

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    Quote Originally Posted by cpickett View Post
    If I was doing this install, I would put a lockable disconnect at the motor, to open the motor leads, and put aux contacts in the disconnect wired to your stop circuit. That way, when the disconnect is open, the drive can't start. The disconnect satisfies LOTO, and prevents the motor from running, and the aux contacts protect the drive if it tries to start with no load (motor) connected.

    Also, if you are using an Allen Bradley drive that has safe torque off (STO) inputs, use those for your e-stop, not the stop input. Other brands have similiar features. That will provide a safety rated way to stop the drive when the e-stop is pushed. Also, it will disconnect power to the motor right away, versus the stop input that may have a ramp time programmed.
    From user safety perspective the aux contact doesn't matter - those are installed to protect the drive, more so to protect from closing the switch when the drive has an active output which can be hard on the drive and not so much of a problem of opening the output circuit when it is active, especially on the drives we see these days, older drives this was even bigger deal to make sure that aux contact opened before the power conductors opened.
    I live for today, I'm just a day behind.

  10. #10
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    Quote Originally Posted by cpickett View Post
    If I was doing this install, I would put a lockable disconnect at the motor, to open the motor leads, and put aux contacts in the disconnect wired to your stop circuit. That way, when the disconnect is open, the drive can't start. The disconnect satisfies LOTO, and prevents the motor from running, and the aux contacts protect the drive if it tries to start with no load (motor) connected.
    Why not on the input supply to the VFD? Wouldn't that be simpler/more effective?

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