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Thread: MCC's with fuses or molded case breakers

  1. #1
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    MCC's with fuses or molded case breakers

    We are having a debate at our site on the safety aspects of using MCC's with fused disconnect vs disconnect that use a molded case breaker. My belief is the fused disconnects are safer as I have a visual indication that the stabs have disengaged...can't tell on the molded case breaker. I know I should test the circuit with a meter on both types of disconnects. It will interesting to see other opinions on this subject. As always many thanks in advance.

  2. #2
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    Quote Originally Posted by cornbread View Post
    We are having a debate at our site on the safety aspects of using MCC's with fused disconnect vs disconnect that use a molded case breaker. My belief is the fused disconnects are safer as I have a visual indication that the stabs have disengaged...can't tell on the molded case breaker. I know I should test the circuit with a meter on both types of disconnects. It will interesting to see other opinions on this subject. As always many thanks in advance.
    The visual verification maybe gives a little more safety feature to that setup. Unless there is an inspection window on the door you still must treat it as though it were live when opening the door to inspect.
    I live for today, I'm just a day behind.

  3. #3
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    Quote Originally Posted by cornbread View Post
    We are having a debate at our site on the safety aspects of using MCC's with fused disconnect vs disconnect that use a molded case breaker. My belief is the fused disconnects are safer as I have a visual indication that the stabs have disengaged...can't tell on the molded case breaker. I know I should test the circuit with a meter on both types of disconnects. It will interesting to see other opinions on this subject. As always many thanks in advance.

    Live/dead/live with ppe on.

  4. #4
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    Quote Originally Posted by cornbread View Post
    We are having a debate at our site on the safety aspects of using MCC's with fused disconnect vs disconnect that use a molded case breaker. My belief is the fused disconnects are safer as I have a visual indication that the stabs have disengaged...can't tell on the molded case breaker. I know I should test the circuit with a meter on both types of disconnects. It will interesting to see other opinions on this subject. As always many thanks in advance.
    It does not really matter. You still have to test to prove it is open even if you can see it.

    I personally have gone away from fuses above 100A or so. Too many times there are no spares and they are not all that easy to come by at 3 am on a sunday morning.
    Bob

  5. #5
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    Quote Originally Posted by cornbread View Post
    We are having a debate at our site on the safety aspects of using MCC's with fused disconnect vs disconnect that use a molded case breaker. My belief is the fused disconnects are safer as I have a visual indication that the stabs have disengaged...can't tell on the molded case breaker. I know I should test the circuit with a meter on both types of disconnects. It will interesting to see other opinions on this subject. As always many thanks in advance.
    Yeah the knives can be disengaged and also be fed from the bottom, making knives hot...
    Always check top and bottom on everything seen broken breaker handles on molded case breakers that looked like they were off but the plastic handle broke internally...

  6. #6
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    Quote Originally Posted by petersonra View Post
    It does not really matter. You still have to test to prove it is open even if you can see it.
    I agree, so the point is moot.

    Fuses can also lead to single phasing, unless you want to put phase fail monitors in every bucket. Now it just got more complicated.

    I like breakers.

  7. #7
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    Quote Originally Posted by petersonra View Post
    It does not really matter. You still have to test to prove it is open even if you can see it.

    I personally have gone away from fuses above 100A or so. Too many times there are no spares and they are not all that easy to come by at 3 am on a sunday morning.
    Quote Originally Posted by Cow View Post
    I agree, so the point is moot.

    Fuses can also lead to single phasing, unless you want to put phase fail monitors in every bucket. Now it just got more complicated.

    I like breakers.
    These cover where I fall; visual indication is irrelevant anyway, Test-Verify-Test still rules the safety roost and despite the rhetoric from fuse mfrs on how much better fuses are, the risks / hassle factor outweighs the benefits to me. I’ve never once seen a piece of EMT used in lieu of a circuit breaker, but I can’t even count how many times I have seen it used as a fuse. The temptation is too great when the production mgr is screaming at you about how he is going to miss his bonus because you don’t have the right fuse at hand...

    That said, if you have more than 100kA available fault current, you will have issues finding small breakers for buckets suitable for that use. But in 40 years, I have never once come across an MCC needing even more than 65kA. I’ve heard people discuss it as if it’s a thing, never come across it.
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  8. #8
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    Surprised by the responses. I realize checking the circuit is required, but I like the visual indication that the stabs are dis-engaged. I have no way of knowing what going on inside the molded case breaker...it was off when I checked it, but internally ... could it fail while I'm working in the bucket (un-likely) but I have no visual indication of anything going wrong. That's why I like the visual indication of open stabs.

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