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Thread: E Stop switch

  1. #1
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    E Stop switch

    I need to replace a shunt trip switch. The 120 volt coil will be LO/TO but the question has come up about the load side wires. They run directly into the 2000 amp breaker.

    Does that breaker need to be shut down . The " WHAT IF " that is being asked is if one of the coil wires came loose inside the 2000 amp breaker and got into the 480 volt while someone is changing the switch.

    I know the chances seem extremely low but i would like some input.

    The 2000 amp breaker is a "R" frame Cutler Hammer.

    I would like to think the coil and mechanism is insulated, isolated or guarded .
    Last edited by ActionDave; 03-16-17 at 12:08 PM. Reason: Restore paragraphs

  2. #2
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    Hard to follow what you are saying. You have a 2000A breaker with a 120V Shunt Trip coil that is tied to a E-Stop PB, right?

    And your question is about what wire coming off and "getting to the 480V"? The 120V circuit conductors feeding the ST coil? If so, does that mean you are working on a 2000A breaker while it is hot???!!!! If so, then you can only do that after a thorough safety risk analysis of the task has been performed and approved by your supervisors and managers, which I would hope had addressed that possibility. If the risk analysis has not been done, technically them allowing you to be exposed to this hazard is potentially a criminal offense, whether you get hurt or not (although if you don't get hurt, it would be up to you to turn them in to OSHA). Step back and think this trough a little more.

    That said, to install the the ST unit on an R frame C-H breaker, you must remove the cover of the entire breaker, exposing yourself to all of the current carrying components, line and load. You would need to be in what will likely be a PPE4 suit and gloves, and the gloves are so thick and stiff that I seriously doubt you can pull it off as a live work task at all.

    If you are doing it de-energized, then if you route the ST circuit conductors as instructed, once you replace the cover on the breaker they are fully isolated from the line voltage.
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  3. #3
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    Lets see if I got this correct

    You have to replace the E stop button in the control circuit, correct?
    You are going to lock out the 120 volts to the coil, correct?
    You are not going into the main panel or breaker, correct?

    If you answered correct to all of the above I think you are fine, you can't play the what if game.
    If that were true you could NEVER work on something fed from a panel because of that "what if a wire comes off and hits the main buss or anouther breaker". You are not exposing yourself to the 480 volts just the "what if".
    A cowboy may get thrown , but they always get up and walk forward.

  4. #4
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    Quote Originally Posted by scott minter View Post
    I need to replace a shunt trip switch. The 120 volt coil will be LO/TO but the question has come up about the load side wires. They run directly into the 2000 amp breaker.

    Does that breaker need to be shut down . The " WHAT IF " that is being asked is if one of the coil wires came loose inside the 2000 amp breaker and got into the 480 volt while someone is changing the switch.

    I know the chances seem extremely low but i would like some input.

    The 2000 amp breaker is a "R" frame Cutler Hammer.

    I would like to think the coil and mechanism is insulated, isolated or guarded .
    If you are only working on the switch that controls the shunt trip you only need to lockout the 120V to that switch. Even if the wires at the breaker somehow connected to the 480V line, there would be no connection to the switch so whoever was working on the switch would still be safe.

    if you are talking about replacing the shunt trip itself, you almost certainly will need to disconnect 480V power to the breaker itself along with the 120V power that powers the shunt trip..
    Bob

  5. #5
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    I am only replacing the switch. Not anything in the 480 breaker or its enclosure. I will LO/TO the 120volt supply.

    The engineer felt concern that the conductors going from the e stop switch are landed inside the 408 2000 amp breaker.

    The chances seem remote that while replacing the e stop switch the other end could get "unlanded" and touch the 480.

    I told him i would ask the group here.

  6. #6
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    Quote Originally Posted by scott minter View Post
    I am only replacing the switch. Not anything in the 480 breaker or its enclosure. I will LO/TO the 120volt supply.

    The engineer felt concern that the conductors going from the e stop switch are landed inside the 408 2000 amp breaker.

    The chances seem remote that while replacing the e stop switch the other end could get "unlanded" and touch the 480.

    I told him i would ask the group here.
    Likely heck no, possible I guess.

    If the engineer wants the 480 shut down I would shut it down. Why fight it?

  7. #7
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    Thanks for all the help.

    No fight just asking opinions.

    I have worked for so long in a government facility i just wondered if it would be common outside.

  8. #8
    The shunt trips in these breakers are installed in a separate "cavity" in the breaker case. The 120V control wire for the shunt trip usually exits a hole on the side of the case (if field installed, it could exit anywhere). The shunt trip solenoid has a plunger that can "exit" the cavity through a tunnel. While it's not wise to ever say "never," there frankly ain't no way any of the shunt trip coil parts are touching the internal breaker bus.

    Having said that - I assume after you wire the switch, you're going to test it - which involves turning off the 480 anyway - so ya might as well turn it off.

    Finally, using a shunt trip as an ESTOP has all kinds of baggage dragging around behind it, but that's a different thread.

    Be safe!

  9. #9
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    Quote Originally Posted by CEDEng View Post
    The shunt trips in these breakers are installed in a separate "cavity" in the breaker case. The 120V control wire for the shunt trip usually exits a hole on the side of the case (if field installed, it could exit anywhere). The shunt trip solenoid has a plunger that can "exit" the cavity through a tunnel. While it's not wise to ever say "never," there frankly ain't no way any of the shunt trip coil parts are touching the internal breaker bus.

    Having said that - I assume after you wire the switch, you're going to test it - which involves turning off the 480 anyway - so ya might as well turn it off.

    Finally, using a shunt trip as an ESTOP has all kinds of baggage dragging around behind it, but that's a different thread.

    Be safe!
    It is probably not really an "estop" as it is probably there to protect equipment rather than human beings.
    Bob

  10. #10
    totally right, bob - the "estop" word has only appeared in responses so far, not from the OP.

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