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switchgear key interlocks, which is true?

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    switchgear key interlocks, which is true?

    im trying to figure out a question i seen on the level 3 test regarding switchgear kirk key interlocks that i havent seen on the practice exam yet. the question went something like this:

    A main tie main configuration is shipped with three locks with a key in each, which is true:

    a. this configuration will work
    b. remove one key and it will work
    c. factory made a mistake
    d. ????

    thats all i can remember and i think i got this one wrong. is there anyone here who has seen this question that can give me some more insight?

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    I wouldn't call it a mistake, switchgear is often shipped with extra keys. Getting rid of one key would allow closure of both mains or one main and a tie. Sounds good to me.

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    Remove one key and it will work. With key interlocks, one less key than the number of interlock cylinders is furnished. An extra key is provided to defeat the interlock under qualified supervision.

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    Quote Originally Posted by electrolyte View Post
    im trying to figure out a question i seen on the level 3 test regarding switchgear kirk key interlocks that i havent seen on the practice exam yet. the question went something like this:

    A main tie main configuration is shipped with three locks with a key in each, which is true:

    a. this configuration will work
    b. remove one key and it will work
    c. factory made a mistake
    d. ????

    thats all i can remember and i think i got this one wrong. is there anyone here who has seen this question that can give me some more insight?
    I would agree with the rest of the comments on this thread. Typically when a new switchgear is purchased, extra keys are sent out. From a test tech standpoint, we use these extra keys to be able to close all mains and ties and are able to do an end to end contact resistance measurement which would include all incoming bus. This of course would not be the only measurement we would do on acceptance. It would also be important to measure contact resistance from the incoming bus to each bus run back in each cubicle. Once our testing is complete, we would remove 1 key before energizing and turn it over to the contractor or owner. This would allow the kirk key interlock system to work as intended. It would never allow both mains and tie breaker to be closed at the same time. If you see these kirk key interlocks, you could also assume that there are no provisions of any type of sync check ensuring both sources were in phase. They could be fed from the same source which means they would be in phase, but that could be a deadly assumption.

    Good Luck

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    Quote Originally Posted by ElectricalTestTech View Post
    If you see these kirk key interlocks, you could also assume that there are no provisions of any type of sync check ensuring both sources were in phase. They could be fed from the same source which means they would be in phase, but that could be a deadly assumption.
    Very true about sync checks, switches and breakers are usually mechanically interlocked for a reason. In some cases you may have to defeat these interlocks by physically removing them. We usually run into a situation like this on maintenance jobs when the customer cant find keys and multiple switches have to be closed for testing. When this happens you have to take extra care to make sure everything goes back the way it was found.

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    Quote Originally Posted by SecondGen View Post
    Very true about sync checks, switches and breakers are usually mechanically interlocked for a reason. In some cases you may have to defeat these interlocks by physically removing them. We usually run into a situation like this on maintenance jobs when the customer cant find keys and multiple switches have to be closed for testing. When this happens you have to take extra care to make sure everything goes back the way it was found.
    I had this question on practice exam. As an option 'D' it was 'remove 2 keys and it will work'.
    I may be wrong, but I think if you read the question careful it says " Which is true?" and the answer to this should be "This configuration will work" because all keys are in place and you can manipulate however you want. The whole purpose of interlocking system that way is defeated, but they don't ask you if interlock system will actually work. With all keys in place you can close/open breakers, however if you want interlock system to be operational as designed than you should remove 1 key. I think it is tricky question and I came across to several questions like this, where the deeper you think on question the further you are from right answer. Some of this questions are easy with straight forward answer but with experience you will try to implement different scenarios which makes it more complex.

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