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Thread: Table 450.3(B)

  1. #1
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    Table 450.3(B)

    Table 450.3(B) indicates that there are two (2) methods for Protection: 1) Primary only protection and 2)Primary and Secondary Protection.

    When are we required to provide secondary protection?

    Do we need secondary protection if we have a current of 9 amperes or more and the primary protection circuit breaker is sized within 125% of the transformer-rated current?

  2. #2
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    Here is a video if you prefer-- https://www.youtube.com/watch?v=tNVoJbhH764

    Look at 240.21(C)
    They say I shot a man named Gray and took his wife to Italy
    She inherited a million bucks and when she died it came to me
    I can't help it if I'm lucky



  3. #3
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    Quote Originally Posted by Malteser View Post
    Table 450.3(B) indicates that there are two (2) methods for Protection: 1) Primary only protection and 2)Primary and Secondary Protection.

    When are we required to provide secondary protection?

    Do we need secondary protection if we have a current of 9 amperes or more and the primary protection circuit breaker is sized within 125% of the transformer-rated current?
    Article 450 is only part of the story for transformer OC protection requirements. As Dennis mentioned see 240.21(C), specifcally 240.21(C)(1). In most cases you will always need secondary protection as most installations are not a 2 wire secondary.
    There is a valid reason for this. Care to think of why?

  4. #4
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