An operator activates the emergency stop button and the machine immediately stops it's motion. The operator then opens an electrically interlocked panel/gate to gain access to point of operation. Once the operator is complete with the "emergency" that caused activation of the E-Stop the operator then closes the electrically interlocked panel/gate and then "pulls" the E-Stop button which automatically re-starts the machine. My question is this acceptable because the interlocked panel/gate is closed or is a another reset function required beyond "pulling" the E-Stop button.
It may be acceptable, but might not be entirely safe. It would seem to me that a machine should not re-start automatically, but should be wired to re-start only when the START button is pushed. OSHA may have some rule on this somewhere.
Like this one from OSHA: (b) Machine controls and equipment. (1) A mechanical or electrical power control shall be provided on each machine to make it possible for the operator to cut off the power from each machine without leaving his position at the point of operation. (2) On machines driven by belts and shafting, a locking-type belt shifter or an equivalent positive device shall be used. (3) On applications where injury to the operator might result if motors were to restart after power failures, provision shall be made to prevent machines from automatically restarting upon restoration of power. (4) Power controls and operating controls should be located within easy reach of the operator while he is at his regular work location, making it unnecessary for him to reach over the cutter to make adjustments. This does not apply to constant pressure controls used only for setup purposes. (5) On each machine operated by electric motors, positive means shall be provided for rendering such controls or devices inoperative while repairs or adjustments are being made to the machines they control. (6) Each operating treadle shall be protected against unexpected or accidental tripping. (7) Feeder attachments shall have the feed rolls or other moving parts so covered or guarded as to protect the operator from hazardous points.
I always use the holding circuit for the E-stop circuit. That way even after the E-stop is reset and closed the machinery won't start until the start button is pressed. I wouldn't think having the machine restart automatically when the E-stop is reset is very safe. I've not come across a set up like that.
I did work on a machine last week that had 4 480V motors and all the coils were 480V. The E-stop circuit was ran in line ahead of one side of all the coils. Same result, you had to hit the start button for a restart after an E-stop.
Re: E-Stops#36468 04/08/0410:52 AM04/08/0410:52 AM
In the plant I work in, LOTO would probably be required if another operator walking by could reset the E-stop and close the gate, injuring the worker attending to the "emergency". OSHA refers to hazardous energy control, and kinetic energy of moving parts (or chemicals, pneumatics, hydraulics, etc.) can be just as deadly as electricity.
FWIW, all the equipment I design has magnetic contactors and the E-stop and interlock devices are always ahead of the start switch/holding contact.
Re: E-Stops#36470 04/09/0406:45 AM04/09/0406:45 AM
We have a couple of those devices in our plant and according to the drawings from the manufactor, they are called stop start switcehs and not e stops. It aloows the operator to clear the line. It will only stop the portion close to him and not the entire machine. All stated e stops do have to be reset before the conveyor will operate
"Yes I am a Pirate, 200 years to late" Jimmy Buffett
Re: E-Stops#36471 04/09/0410:42 AM04/09/0410:42 AM
My experience with E-stops at my work, they are too, on the holding circuit. By pulling the e-stop cable, the conveyor then stops and must be restarted with the start/stop buttons. This prevents restarting the conveyor until you are clear. However this should never be used as a means of stopping the equipment for repair. This is only method to stop the equipment immediately. If you intend to repair it, then it MUST be locked and tagged out.