I have a couple machines that where bought on auction from who knows where. The E-stop circuits on these machines consist of 3 E-stop buttons with N.O contacts which are wired to the shunt trip circuit breaker that provides the power to the machine. I have built some redundant circuits and relay logic to make it as fail safe as possible except I still can't get around the fact that I need 110vac power to actually trip the breaker. I don't believe this circuit in anyway can truly be made fail safe. Any ideas or alternative options. I plan to add in a contactor, but this is a 175a circuit with limited space in the cabinet.
Shunt trip
- Thread starter jwhit
- Start date
- Status
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
If the equipment is 120 volt, then just take the source of power for the shunt trip from the power to the equipment. If it is 480 volt, then I suspect you already have a control power transformer somewhere in the starter, and you can take power from it. The point is, if you don't have power to the shunt trip, then you don't have power to the equipment, so you don't need to trip the equipment. Finally, just make sure the equipment cannot automatically restart on restoration of power, without an operator hitting the "start" button. That's about as fail safe as you can get.
- Location
- Massachusetts
Charlie's suggestions sound great.
Adding normally open contactors on the load side of the breakers would be another option.
You need someone to respond who is familiar with the rules for machinery but I do not believe E-stops for motors can be wired normally open.
Adding normally open contactors on the load side of the breakers would be another option.
You need someone to respond who is familiar with the rules for machinery but I do not believe E-stops for motors can be wired normally open.
peteo
Senior Member
- Location
- Los Angeles
"I don't believe this circuit in anyway can truly be made fail safe." I agree with that statement. Sounds goofy.
A contactor control circuit with control power routed through NC stop & Estop buttons in series, to a NO auxiliary contactor relay set (paralleled with a NO start button) would be supervised. The point being, of course, that if anything happens the e-stop function will activate.
That setup will be huge unless you go an IEC, versus NEMA, contactor. May be that you'll need to replace the buttons. Finally, if you add a transformer in for a control circuit: Fuse both output legs; get a transformer with a white center tap wire; and connect that center tap solidly to electrical ground.
A contactor control circuit with control power routed through NC stop & Estop buttons in series, to a NO auxiliary contactor relay set (paralleled with a NO start button) would be supervised. The point being, of course, that if anything happens the e-stop function will activate.
That setup will be huge unless you go an IEC, versus NEMA, contactor. May be that you'll need to replace the buttons. Finally, if you add a transformer in for a control circuit: Fuse both output legs; get a transformer with a white center tap wire; and connect that center tap solidly to electrical ground.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
shunt trip
shunt trip
An assumption is being made that the buttons involved are emergency stop buttons.
Maybe they are only stop buttons.
There is no NEC requirement that a motor have an estop pb on it. It might be advisable, or required if the motor is part of a machine that may need it, but that is a safety issue, not a NEC issue.
shunt trip
An assumption is being made that the buttons involved are emergency stop buttons.
Maybe they are only stop buttons.
There is no NEC requirement that a motor have an estop pb on it. It might be advisable, or required if the motor is part of a machine that may need it, but that is a safety issue, not a NEC issue.
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