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Thread: Hazardous area class1, Group B disconnect rules.

  1. #1
    Join Date
    Oct 2010
    Location
    Lagrang, Ohio
    Posts
    5

    Hazardous area class1, Group B disconnect rules.

    Using a FSQC2390 Cooper Crous-Hinds disconnect interlocked 3 pole 4-wire 480vac 2 HP at Vfd driven aggitator motor what is the best way to
    perform the isolation.
    !1way is to interlock run enable vfd circuit through 1 set of poles and let vfd perform isolation or 2nd method let disconnect perform by switching all 3 poles.
    But I want to ensure that plug is in place to prevent run feedback from showing run when in fact plug is disconnected. Also to prevent drive from starting when plug is inserted and start command is allready in place.
    Manual is showing 1st option using a contactor to perform the interlock function. I have a cuttler hammer vfd drive with-out a contactor but a run enable digital input to prevent drive from starting using only 1 set of poles ang passing through the 480vac through FSQC2390.
    What NEC codes apply? Thanks.

  2. #2
    Join Date
    Aug 2004
    Posts
    11,542
    Can you draw a sketch of what you propose doing and define a little more why you are doing this?

    I do not think OSHA would approve isolating the motor solely by opening the VFD enable line.
    Bob

  3. #3
    Join Date
    Oct 2010
    Location
    Lagrang, Ohio
    Posts
    5

    Attached example of proposed wiring.

    bcw.pdf

    They are using motor control contactor in this example. Do I have to add MCR relay at output of vfd drive to perform this function?
    Plant has used these disconnects for many years in both the control wire break 2-pole only or incoming 480vac 3-pole.

  4. #4
    Join Date
    Aug 2004
    Posts
    11,542
    If you are actually trying to disconnect the motor (such as for lockout/tagout purposes) you can't use a contactor or the enable line of a VFD. It is just not safe "enough".
    Bob

  5. #5
    Join Date
    Oct 2010
    Location
    Lagrang, Ohio
    Posts
    5

    Purpose of isolating this aggitator motor with physical disconnect plug to insure.

    With Vfd drive located on other side of bldg. the method of adding physical plugs to disconnect ensures is isolated for tank entries.
    Hazardous area maakes this disconnect difficult to spec or I would use a Hubble circuit -lok disconnect with additional aux contacts to perform
    the 480vac isolation as well as monitor the state of disconnect with aux contact wired in start circuit.

  6. #6
    Join Date
    Feb 2003
    Location
    Illinois
    Posts
    19,298
    This is a lockout and the lockout device itself must physically open the power circuit. Interlocks or other types of controls cannot be used for lockout purposes. Meltric makes disconnect rated for Class I, Division 2, Groups A, B, C, & D, but I don't think it has auxiliary contacts for the control circuit like their non-hazardous area one do.
    Don, Illinois
    "It is the first responsibility of every citizen to question authority." B Franklin

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