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E Stop switch

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scott minter

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Location
Kennedy Space Center, Florida
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Associate Engineer
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 .
 
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Jraef

Jraef

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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.
 
just the cowboy

just the cowboy

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Location
newburgh,ny
Lets see if I got this correct

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".
 
petersonra

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
scott minter said:
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 .
Click to expand...

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..
 
S

scott minter

Member
Location
Kennedy Space Center, Florida
Occupation
Associate Engineer
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.
 
iwire

iwire

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Location
Massachusetts
scott minter said:
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.
Click to expand...

Likely heck no, possible I guess.

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

CEDEng

Member
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!
 
petersonra

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
CEDEng said:
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!
Click to expand...

It is probably not really an "estop" as it is probably there to protect equipment rather than human beings.
 
S

scott minter

Member
Location
Kennedy Space Center, Florida
Occupation
Associate Engineer
Good Afternoon

It is an e stop according to the Square D box. It has a break glass button holding contacts open.

When you break the glass it releases the button making the circuit. It was requested by our fire dept.

at each door to de-energize the MCC before entry in case of fire. That is the reason for the original install.

During a PMI it was noticed the contact and screws were rusted and cracking the plastic contact block housing.

I am replacing the contact block inside the e-stop.

Our engineer was concerned about the load side wires "IF" anything could happen.

Thank you everyone for the input.
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
For what it is worth the function you describe makes it not an emergency stop. Emergency stops have very specific rules and a shunt trip would not be part of it.

You are describing what many would call an 'EPO' Emergency Power Off button.
 
C

CEDEng

Member
HA sheesh you're right - right there in the topic. I only referred to the body, where it wasn't mentioned.

not enough coffee...too much coffee...old age...hard to say...

Sounds like you're all resolved, but I agree with what was previously posted: This is an EPO circuit, emergency power off, not an ESTOP. Semantics perhaps, but you'd get very different responses about this if it were indeed an ESTOP.
 
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