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Thread: Overcurrent devices rated over 800 amps

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    Overcurrent devices rated over 800 amps

    240.4 (C) States that the ampacity of the conductors it protects shall be equal to or greater than the rating of the overcurrent device. I understand that.
    If I have an adjustable trip circuit breaker that is adjusted to the load do I still have to size the conductors to the breaker rating or can I size them to the load?
    This would be covered by 240.6 (C).
    Sometimes I don't know whether I'm the boxer or the bag.

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    Quote Originally Posted by qcroanoke View Post
    240.4 (C) States that the ampacity of the conductors it protects shall be equal to or greater than the rating of the overcurrent device. I understand that.
    If I have an adjustable trip circuit breaker that is adjusted to the load do I still have to size the conductors to the breaker rating or can I size them to the load?
    This would be covered by 240.6 (C).
    If the adjusted rating of the circuit breaker was 1100A, for instance, per 240.6(C), then the ampacity of the conductors it is protecting needs to be at least 1100A.

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    Quote Originally Posted by david luchini View Post
    If the adjusted rating of the circuit breaker was 1100A, for instance, per 240.6(C), then the ampacity of the conductors it is protecting needs to be at least 1100A.
    If its a 1600 amp breaker adjusted to 1240 amps the wire can be sized to 1240 amps and not 1600 amps? per 240-6.(C)
    Sometimes I don't know whether I'm the boxer or the bag.

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    Quote Originally Posted by qcroanoke View Post
    If its a 1600 amp breaker adjusted to 1240 amps the wire can be sized to 1240 amps and not 1600 amps? per 240-6.(C)
    Yes

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    Implicit in that is the expectation that only electrically qualified personnel will be allowed to adjust the trip point of the breaker.

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    Quote Originally Posted by GoldDigger View Post
    Implicit in that is the expectation that only electrically qualified personnel will be allowed to adjust the trip point of the breaker.
    Specifically meaning that it is behind locked doors, locked gates, locked equipment dead-fronts, or any combination of the aforementioned, so that the general occupants of the premises cannot get to it and change the setting.

    This is the norm for any place of public accommodation, as any large equipment is likely in a locked electrical room anyway. But one place you might see breakers of this ampacity NOT locked, is in an industrial or warehouse application, where the general staff members walk by it all the time, and it isn't access controlled to exclusively the electrically qualified personnel.

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    Quote Originally Posted by Carultch View Post
    Specifically meaning that it is behind locked doors, locked gates, locked equipment dead-fronts, or any combination of the aforementioned, so that the general occupants of the premises cannot get to it and change the setting.

    This is the norm for any place of public accommodation, as any large equipment is likely in a locked electrical room anyway. But one place you might see breakers of this ampacity NOT locked, is in an industrial or warehouse application, where the general staff members walk by it all the time, and it isn't access controlled to exclusively the electrically qualified personnel.
    It can be behind a sealed cover on the breaker

    Restricted access shall be defined as located behind
    one of the following:
    (1) Removable and sealable covers over the adjusting means
    (2) Bolted equipment enclosure doors
    (3) Locked doors accessible only to qualified personnel

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