E-STOP OPERATION

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ctroyp

Senior Member
I wasn't real sure where to post my question but here it is:
E-stops are used to remove power from a machine in order to stop all hazardous movement. I have an issue in our plant that provides another problem. When an e-stop is actuated, the tandem machines stop at different rates when power is applied. This creates a hazard of breaking the product (wire) between the two machines. Although it would momentarily require the presence of power during an e-stop condition, can I implement a decelleration rate on the machine upstream to keep it from lagging behind and snapping the wire? The estimated e-stop sequence would be modified from appx. 3 seconds (with removal of power, ) to appx. 7 seconds which is close to the rate of the downstream machine. Would this violate any OSHA reg, etc. The intent is to remove any danger from the operator and eliminate product/equipment damage.
 

rbalex

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Location
Mission Viejo, CA
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Professional Electrical Engineer
Re: E-STOP OPERATION

The concept of orderly shutdown is recognized in NEC Art 685. Table 685.2 refers to other Sections where the concept is applied.

As a base fundamental, it must be shown that there would be no increased or additional hazards to personnel if the shutdown process were extended from three to seven seconds.

You may, in fact, assert that preventing the snapping of the wire would increase safety. In any case, FedOSHA and 685.1(3) would mandate that all other reasonable mitigation methods had been applied.
 

jim dungar

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Wisconsin
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PE (Retired) - Power Systems
Re: E-STOP OPERATION

The specific aspects of machine control is not part of the NEC. A better standard is NFPA79 "Electrical Standard for Industrial Machinery". NFPA79 9.2.2 describes three categories of emergency stop. Your application would be a category 1, which allows for a controlled stop with final (total) removal of power after a full stop has been achieved.

[ April 27, 2005, 04:06 PM: Message edited by: jim dungar ]
 

Duuuuug

Member
Re: E-STOP OPERATION

Just curious, why can't the 7-second machine be stopped in 3 seconds.
I work with tobacco and foam processing machinery and 7 seconds an awful long time for any process to come to a stop.
 
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