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Thread: Deadman switch at aviation fuel tank

  1. #1
    Join Date
    Jul 2010
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    Deadman switch at aviation fuel tank

    I am replacing a deadman switch that is in a nema 3 box which they've ran sealtight to. It comes from an explosion proof box that does have a sealoff before it changes over to sealtight. The switch has 240v at the handle. When I replace it I'm going to step it down to millivolts. I'll put my transformer in an EP box but am I good to leave the sealtight from that point to the N3 box the handle is in?

  2. #2
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    Quote Originally Posted by LeoJackson View Post
    I am replacing a deadman switch that is in a nema 3 box which they've ran sealtight to. It comes from an explosion proof box that does have a sealoff before it changes over to sealtight. The switch has 240v at the handle. When I replace it I'm going to step it down to millivolts. I'll put my transformer in an EP box but am I good to leave the sealtight from that point to the N3 box the handle is in?
    Leo -
    It sounds like you are you're changing the design - Maybe to intrinsically safe, or non-incindive. I'd recommend finding the area classification drawing for the facility.

    You may need to have a control drawing.

    cf

  3. #3
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    Quote Originally Posted by Cold Fusion View Post
    Leo -
    It sounds like you are you're changing the design - Maybe to intrinsically safe, or non-incindive. I'd recommend finding the area classification drawing for the facility.

    You may need to have a control drawing.

    cf
    Correct I am changing the design because of both the reasons you mention. My question is after it's stepped down to millivolts is a sealoff neccessary going to my switch? And is sealtight alright to use?

  4. #4
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    Quote Originally Posted by LeoJackson View Post
    Correct I am changing the design because of both the reasons you mention. My question is after it's stepped down to millivolts is a sealoff neccessary going to my switch? And is sealtight alright to use?
    I should have been more clear.

    It will either be non-incindive or intrinsically safe - not both.

    Your answer will be in the Control Drawing or on the area classification drawing. Since you are doing the redesign, you are the engineer of record. You will either need to find, or draft those two documents.

    500.2 Definitions.
    Control Drawing.
    A drawing or other document provided by the manufacturer of the intrinsically safe or associated apparatus, or of the nonincendive field wiring apparatus or associated nonincendive field wiring apparatus, that details the allowed interconnections between the intrinsically safe and associated apparatus or between the nonincendive field wiring apparatus or associated nonincendive field wiring apparatus.

    500.4 General.
    (A) Documentation. All areas designated as hazardous (classified) locations shall be properly documented. This documentation shall be available to those authorized to design, install, inspect, maintain, or operate electrical equipment at the location.

    This is generally the area classification drawing.

    If I were doing the job, those would be the first two documents I would find.

    cf

  5. #5
    Join Date
    Feb 2003
    Location
    Illinois
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    19,508
    That is a safety system and the design should not be changed without an evaluation by an engineer. It sounds like the current system actually interrupts the current to the pump motor and the introduction of a power supply and relays or contactors could make the system less reliable.
    Don, Illinois
    "It is the first responsibility of every citizen to question authority." B Franklin

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