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Thread: Should a Dry Type Transformer be mounted inside or outside of electrical enclosure?

  1. #1
    Associate Engineer
    Join Date
    Mar 2013

    Should a Dry Type Transformer be mounted inside or outside of electrical enclosure?

    I wanted to get some opinions on if a NEMA-3R dry-type distribution small transformer (2- 7.5 KVA) should be mounted on the inside or outside of the main free standing electrical enclosure. Does the location of the transformer matter to protect someone from Arch Flash. Is a person more at risk from arch flash if the transformer is mounted on the outside of an electrical enclosure? I can think of good reason for both locations:

    Transformer inside enclosure
    1. The enclosure will have a cleaner appearance.
    2. Easier wiring since all wiring is inside enclosure.
    2. wiring since all wiring is inside enclosure.

    1. There is more heat dissipated inside the enclosure
    2. Takes up more space inside enclosure
    3. Temperature inside enclosure is increased which requires larger cooling fans.
    4. Component life is reduced due the increase temperature.
    5. More difficult to physically install to mount a 100lbs transformer inside enclosure

    Transformer outside enclosure
    1. Enclosure size can be smaller since transformer can be mounted on outside.
    2. Less heat dissipation so inside electrical components are cooler which they will last longer.
    3. Transformer will be easier to install physically since a lift, etc can be used on outside to hold transformer into position to tighten bolts, etc.

    1. The appearance does not look as nice and clean since you have this large object hanging off the side.
    2. wiring a little more difficult since have to put hole through enclosure to run electrical wiring to transformer.
    3. People can lean, sit, leave objects: liquid, tools, etc on transformer.
    4. Transformer is stick out so someone might run into the transformer and cut there arm etc. on end of transformer.

    Any opinions would be greatly appreciated on where control engineers mount their NEMA-3R distribution dry type transformers. Thanks for your time and help in advanced.

  2. #2
    Associate Engineer
    Join Date
    Apr 2013
    why spend the extra money for transformer inside an enclosure only to mount it inside the panel?
    what is the working environment?

  3. #3
    Here is my opinon,

    If your transformer is IP69 (operable in harsh weather) then why spend the extra time and money to mount a outdoor transformer inside a outdoor enclosure.

    I am assuming this is to be pole mounted? If so, simply attach the transformer using the manufacturers standard pole support structure and then have the electronics enclosure mounted on the opposite side of the pole, a safe distance from the transformer (EMI).

    Easy peasy!

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