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Thread: Dry Type Transformers in CL-1 DIV-2 area

  1. #1
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    Dry Type Transformers in CL-1 DIV-2 area

    In what case can you install a Dry Type Transformers like G.E. #9T23Q3071 in a class 1 div2 a,b,c,d area.

  2. #2
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    There are no special rules for transformers in Class I, Divison 2 areas. Note, I have not looked up that part number but if it is one of the GE dry transformers that has cooling fans, then there may be an issue with the fan controls. 501.100(B).
    Don
    Don, Illinois
    "It is the first responsibility of every citizen to question authority." B Franklin

  3. #3
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    You have asked a very general question about a very specific transformer.

    The “general” part of the answer, Section 501.100(B), is in Division 2, the transformer would need to be installed per Sections 450.21 to 450.27.

    According to the GE Buylog a 9T23Q3071 is 15kVA, 480 - 208Y/120 V, indoor, with an 80C rise.

    With this information the transformer would be installed per Section 450.21(A). If installed with a weather shield, the appropriate Section would be 450.22.

    Normally, this would be the end of the analysis; however the 80C rise also needs some attention. This would give the transformer a UL Temperature Class of 150C. This is arrived at by the sum of 40C assumed ambient plus the 80C rise plus a 30C assumed “hot spot”. Since there is no “T-code” that directly correlates to 150C, the next higher (160C or "T-code" T3C) should be used. Edit add: See Sections 500.8(B)(4) and 500.8(C)(1)

    The only open question is the actual gas or vapor involved. For Groups A and B, the auto-ignition temperature for the materials involved are well above a 160C. Most are for Groups C and D also, but they must be reviewed.

    Per Section 500.8(B)(6)(a), no special markings are required.
    Last edited by rbalex; 11-24-07 at 01:32 PM.
    "Bob"
    Robert B. Alexander, P.E.
    "I know that you believe you understand what you think the NEC says, but I am not sure you realize that what you read is not what it means." (Corollary to Charlie's Rule)

  4. #4
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    Thanks for the info, I'm working in Saudi on a project and the transformers above are installed in a Ethylene unit and they do have the weather shield on them. The transformers are on the ground,I work in a Ethylene back home and we use the encapsulated type.

  5. #5
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    Per NFPS 497, ethylene is Group C and has an AIT of 450C. It is a broadly used material common enough that it has been classified by test.
    "Bob"
    Robert B. Alexander, P.E.
    "I know that you believe you understand what you think the NEC says, but I am not sure you realize that what you read is not what it means." (Corollary to Charlie's Rule)

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